oEPA
United States
Environmental
Protection Agency
EPA/600/R-25/115 | May 2025 | www.epa.gov/research
BEST PRACTICES GUIDE FOR
IMPROVING INDOOR AIR
QUALITY IN COMMERCIAL/
PUBLIC BUILDINGS DURING
WILDLAND FIRE SMOKE A
EVENTS .^A
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&EPA
U.S. Environmental Protection Agency
Amara Holder, Ph.D.
Office of Research and Development
Center for Environmental Measurement and Modeling
U.S. Environmental Protection Agency
Research Triangle Park, NC
Beth Hassett-Sipple, MSPH (Retired)
Office of Research and Development
Center for Public Health and Environmental Assessment
U.S. Environmental Protection Agency
Research Triangle Park, NC
Sarah Coefield, MS, MA
Office of Research and Development
Center for Public Health and Environmental Assessment
U.S. Environmental Protection Agency
Research Triangle Park, NC
Olivia S. Ryder, Ph.D., and Hilary R. Hafner
Sonoma Technology
Petaluma, CA
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This document has been reviewed in accordance with U.S. Environmental Protection Agency policy
and approved for publication. The United States Environmental Protection Agency through its Office
of Research and Development funded and managed the work described here under EPA Contract
Number/Order No. 47QRAA18D00D1 with Sonoma Technology. Mention of trade names or
commercial products does not constitute endorsement or recommendation for use.
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Contents
Section Page
PURPOSE OF THIS PUBLICATION 1
INTENDED AUDIENCE 1
1. INTRODUCTION TO WILDLAND FIRE SMOKE 4
1.1 Health Impacts from Smoke 5
1.2 Smoke Information Sources 6
1.3 Smoke Impacts Indoors 9
1.4 Strategies for Improving Indoor Air Quality During Outdoor Smoke Events 10
2. HVAC SYSTEMS: IMPROVEMENTS AND RECOMMENDED SETTINGS 12
2.1 Overview of HVAC Systems 13
2.2 Air Flow Optimization 17
2.3 HVAC Run Time Changes 19
2.4 Filtration 20
2.5 Supplemental External Filtration 23
3. BUILDING USAGE AND WEATHERIZATION ADJUSTMENTS 26
3.1 Overview 26
3.2 Sealing the Building 26
3.3 Entrance Adjustments 28
4. PORTABLE AIR CLEANERS (PACS) 30
4.1 Overview 30
4.2 When to Use a PAC 31
4.3 Types of Air Cleaners 31
4.4 How to Select a PAC 34
4.5 Other Considerations 37
4.6 Filter Replacement and Maintenance 38
4.7 Creating a "Cleaner Air Room" 39
5. AIR SENSORS 41
5.1 Overview 41
5.2 Choosing an Air Sensor 42
5.3 Installing Air Sensors Indoors 42
5.4 Multiple Sensors 45
5.5 Using Air Sensor Data During a Smoke Event 47
5.6 Caveats and Cautions 49
APPENDIX 1: BUILDING SMOKE-READY PLANNING 50
APPENDIX 2: RESOURCES FOR INDOOR AIR QUALITY 63
APPENDIX 3: GLOSSARY OF TERMS 67
APPENDIX 4: HOW TO PERFORM AN AIR SENSOR PRECISION CHECK 71
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Acknowledgments
This report is the result of the support of numerous individuals who aided in its development and
provided peer review. Their contribution is briefly described and acknowledged below.
Aided in Development:
Wayne Cascio - Center for Public Health and Environmental Assessment, ORD, EPA
Stacey Katz - Center for Public Health and Environmental Assessment, ORD, EPA (Retired)
Bryan Hubbell - Air, Climate, and Energy Research Program, ORD, EPA
Tom Javins - Facilities Services, University of Montana (Retired)
Gail Robarge - Center for Public Health and Environmental Assessment, ORD, EPA (Retired)
Gina Solomon - Division of Occupational, Environmental and Climate Medicine, University of
California San Francisco
Peer Reviewers:
Christina Baghdikian - Center for Computational Toxicology and Exposure, ORD, EPA
Christopher Caler - Office of Radiation and Indoor Air, OAR, EPA
Randolph Chapman - Office of Radiation and Indoor Air, OAR, EPA
Serena Chung - Office of Science Advisor, Policy, and Engagement, ORD, EPA
Woody Delp - Energy Analysis & Environmental Impacts Division, Lawrence Berkeley National
Laboratory
Abby Hall - (Formerly) Office of Policy, EPA
Mohammad Hiedarinejad - Department of Civil, Architectural, and Environmental Engineering, Illinois
Institute of Technology
Bryan Hubbell - Air, Climate, and Energy Research Program, ORD, EPA
Tom Javins - Facilities Services, University of Montana (Retired)
Beth Landis - Office of Radiation and Indoor Air, OAR, EPA
Daniel Malashock - Office of Radiation and Indoor Air, OAR, EPA
Rachel Mclntosh-Katrinsky - Office of Air Quality Planning and Standards, OAR, EPA
Erin McTigue - Air and Radiation Division, R10, EPA
Alison Savage - Office of Radiation and Indoor Air, OAR, EPA
Brent Stephens - Department of Civil, Architectural, and Environmental Engineering, Illinois Institute
of Technology
McKenna Thompson - Office of Environmental Health Hazard Assessment, California Environmental
Protection Agency
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Purpose of this
Publication
This publication provides recommendations
and resources to reduce indoor exposure to
elevated particulate matter (PM) and gaseous
pollutant concentrations in public, commercial,
and multi-unit residential buildings during
wildland fire (see Terminology box) smoke
events.
Note this document is intended to inform
actions to minimize smoke impacts indoors
and create a Smoke-Ready Plan. It is not
intended to address all aspects of indoor air
quality. A Smoke-Ready Plan is a list of actions
to take before, during, and after a smoke event.
Intended Audience
This publication is for (1) individuals and
groups with decision-making abilities for
public, commercial, and multi-unit residential
buildings including building owners and
managers, school administrators, and facility
managers; (2) federal, state, local, and Tribal
environmental and public health organizations
that provide information to communities to
reduce exposure to wildland fire smoke in
public or commercial spaces.
This document is not intended to provide a
rigorous review of mitigation measures for
technical audiences. Heating, Ventilation and
Air Conditioning (HVAC) professionals,
architects, design engineers, and construction
contractors should consult standards and
guidance for their industry and the ASHRAE
Guideline 44-2024, Protecting Building
Occupants from Smoke During Wildfire and
Prescribed Burn Events.1
1 This guideline is available from the ASHRAE Bookstore at https://store.accuristech.com/ashrae/standards/auideline-
44-2024-protectina-buildina-occupants-from-smoke-durina-wildfire-and-prescribed-burn-
events?product id=2923808
Terminology
The term "wildland fire" is overarching and
describes fire that occurs in wildland
vegetation. The term encompasses both
prescribed fire and wildfire (below).
Wildland Fires
r 1 D
Wildfires Prescribed Fires
A graphical representation of wildfires and
prescribed fires, both of which are included in
the term "wildland fires".
A prescribed fire is a planned fire
intentionally ignited to meet land
management objectives such as restoring
ecosystem health and reducing vegetation
buildup. A wildfire is an unplanned fire
which may be caused by lightning or other
natural causes or by human ignitions,
accidentalor intentional. Prescribed fires are
typically planned when weather conditions
are favorable for keeping the fire under
control and minimizing smoke impacts to
population centers.
Individual prescribed fires are typically short
duration, e.g., hours to days, but there may
be many occurring at the same time in some
regions during some parts of the year.
Wildfires can last weeks to months during dry
periods and often impact the western U.S.
during the summertime.
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Table 1 provides a roadmap of this
best practices guide and identifies
sections/topics that may be of most
use. Each section of this guide starts
with a "Be Smoke Ready" overview box,
intended to provide a shortlist of actions
to perform:
Ol Before a smoke event
During a smoke event (or when smoke
is forecast)
After a smoke event
The same symbols used in the overview boxes
can be found throughout the text to help the
reader find more information about the
recommended actions.
Table 1. A roadmap of this best practices guide for readers to identify which sections are most
applicable to their building's HVAC characteristics.
Section
Centralized
HVAC system
Industrial or
commercial grade
Centralized HVAC
system
Residential grade
Standalone AC
Single or multiple
units
No existing air
conditioning in
building
1. Wildland Fire Smoke
Background information on
smoke impacts on air quality
2. HVAC
Information for understanding
your system and how to adjust it
during smoke events
3. Building Usage &
Weatherization
Controlling building infiltration
and leaks
A. Portable Air Cleaners
Using additional filtration
methods to improve indoor air
quality
5. Air Sensors
Leveraging air sensors for
monitoring indoor pollutant
levels
Key relevant sections
Secondary sections that may also
prove useful
2
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Managing Smoke and Airborne Virus Concerns
Veatyuboa, the amount a:* c= I? ruuyiay ii;
aad oat of a buiUdog, i a a a important
component of indoor air quality
mnn.icemont.
increading ventilation is a principal way of
reducing the spread of common
respiratory viruses indoors and
concentrations from indoor sources of air
polio iion.. Hoc;ov o r, rc oornrnanriariona for
vv::a;: to increase the amount of
ventilation may differ depending on
certain situations, such da when smoke is
affectiny outdoor air quality.
[Junoy smoke cmisodes, whoa it is
im pott ant to reduce the a mount ot smoke
that makes it ways indoors, ventilation
should be minimized Lo pud. in as hide
outdoor air as possible.
However, when smoke episodes occur at
the same time as periods ot increased
illness in a baildiny or roam:unity,
building decision makers vvid. need to
baianco the chadonees of adequate
voatibrnon by monitoring indoornnd
outdoor conditions, and admating building
o p e r a t i o n s a p p r o p r i a t e ly.
Here are two common approaches to help
with airborne virus spread and smoke
reduction indoors:
c fsicreaslng indoor filtration rates using
Sue central HVAC system by increasing run
time aad/or upgrading to a more efficient
fiber. This can reduce both r.on cent rat ions
of smoke and virus particles when
ventilation with outdoor air :s not possible
and may need to no done in recirculation
or fan only modes during smoke events.
y. Using Portable Air Cleaners IPAC s) with
effective pnrtici- filtration to rodoce
suioke and virus particles induum.
for more information, see the indoor Air
Quality and Airborne Viruses' section of
Appendix: Resources for indoor Air Quality.
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1. Introduction to
Wildland Fire Smoke
Wildland fire smoke is a complex mixture of PM
and gases. Its composition is closely related to
fire and weather conditions and the material
burned, which differs between fire events. For
example, prescribed burns and some wildfires
burn purely vegetation (e.g., plants and trees),
while wildfires in the wildland urban interface
(WUI) - where the built environment adjoins
with the natural environment - can also burn
vehicles, and structures.
Wildland fire smoke consists of both fine
particles (particles less than 2.5 pm in diameter,
known as PM2.5) and coarse particles (known as
PM io-2.b, which are particles smaller than 10 |jm
and larger than 2.5 pm in diameter). The PM2.5
portion is mostly composed of submicron
particles (smaller than 1 pm in diameter).2
PM2.5 is formed during combustion, while
PM 10-2.5 consists of larger ash particles that
remain after material is burned and can include
windblown soil. PM2.5 is the main PM
component of smoke and poses the greatest
short-term (i.e., days to weeks) risk to public
health because these particles can penetrate
deep into the lungs and enter the
bloodstream.3
Figure 1 shows general categories of
pollutants produced during wildland fires
Smoke also contains polycyclic aromatic
hydrocarbons (PAHs) and pollutant gases,
including carbon dioxide (CO2), carbon
monoxide (CO), nitrogen oxides (NOx), and
volatile organic compounds (VOCs)4. Some
hazardous VOCs produced by wildland fires
General Components of Wildland Fire Smoke
largest <ฆ-
smallest
Total Particulate
Matter
PAHs
(polycylic aromatic
hydrocarbons)
Gases
Soot Organics
ik
&
VOCs Carbon Nitrogen Carbon
(volatile Dioxide Dioxide Monoxide
organic
compounds)
Fuel Sources: Trees, Natural Vegetation, Structures, and Vehicles
Figure 1 Typical components of wildland fire smoke.
2 https://acp.copernicus.Org/articles/5/799/2005/
3 https://www.epa.gov/wildfire-smoke-course/whv-
wildfire-smoke-health-concern
4 VOCs are a diverse class of compounds with varied
effects on health. For more information, see
https://www.epa.gov/indoor--air--qualitv--iaq/volatile-
oraanic-compounds-impact-indoor-air-qualitv
4
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include acetaldehyde, acrolein, formaldehyde,
and benzene. This publication primarily
focuses on indoor PM and VOC reduction
strategies.
1.1 Health Impacts from
Smoke
Both PM2.5 and VOCs in smoke present health
risks. PM2.5 is the pollutant of greatest concern
because it is a major component of smoke and
there is extensive scientific evidence that show
its impact on health.5 Short-term exposure to
high concentrations of PM can lead to
respiratory symptoms, reduction in pulmonary
function, airway inflammation, and aggravate
chronic heart and lung diseases. Prolonged
exposure to PM2.5 can lead to decreased lung
function and increased respiratory symptoms.
Short-term exposure to high concentrations of
VOCs can lead to health effects including eye,
nose, and throat irritation; headaches; nausea;
and dizziness. Prolonged exposure to certain
VOCs has been linked to cancer.
Certain life stages and populations may be at
greater risk of experiencing health effects and
may experience more severe effects due to
wildland fire smoke exposure. These groups are
referred to as at-risk populations or "sensitive
groups" (used in the Air Quality Index, see
Table 2).6
Smoke exposure in people with asthma and
other lung diseases can lead to breathing
issues, coughing, wheezing, chest tightness,
and worsening of lung diseases. For those with
pre-existing cardiovascular diseases, smoke
exposure can trigger heart attacks and stroke.
Children under 18 tend to spend more time
outdoors and inhale more air per pound of
body weight compared to adults, both of which
impact the dose of smoke they experience and
their risk of health effects. Children are also at
greater risk of smoke-related health effects
because their lungs are still growing. As such,
they are more susceptible to breathing
problems such as coughing, wheezing, chest
tightness, and decreased lung function. Older
adults (65 years of age or older) are more likely
to have chronic lung or heart conditions and
thus are at risk of exacerbating these
conditions with smoke inhalation. In addition,
the body's ability to respond to health
challenges generally declines with age.
Pregnancy increases breathing rates, which
may lead to increased smoke sensitivity. Smoke
inhalation may lead to gestational diabetes,
high blood pressure, low birth weight, or pre-
term birth.
People of low socio-economic status may have
reduced access to health care resources,
leading to undiagnosed underlying health
conditions, including asthma and diabetes.
They may also have reduced access to wildland
fire smoke mitigation measures (e.g., air
cleaners), be more likely to live in leaky housing
with less access to air conditioning, or be
unhoused.
During smoke episodes, outdoor workers are
exposed to high concentrations of PM2.5 for
extended periods of time, which can result in
worsening of health conditions.
5 Cascio, 2017,
https://doi.ora/10.1016/i.scitotenv.2017.12.086
6 Which Populations Experience Greater Risks of
Adverse Health Effects Resulting from Wildfire
Smoke Exposure? https://www.epa.gov/wildfire-
smoke-course/which-populations-experience-
greater-risks-adverse-health-effects-resultina
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For more information on health impacts from
smoke, see the Wildfire Smoke Fact Sheet: At-
Risk Groups of People.7
1.2 Smoke Information
Sources
The Air Quality Index
The U.S. EPA has established the Air Quality
Index (AQI)8 to aid public understanding of
outdoor air quality based on pollutant
concentrations and it can be used to trigger
actions to improve indoor air quality. The AQI
converts pollutant concentrations to a number
on a scale from 0 to 500. These values are tiered
into six color-coded categories that provide
information about potential health effects and
protective actions. Higher AQI values
correspond to greater levels of air pollution
and higher health concern (Table 2). In lower
AQI categories, different groups of people are
anticipated to experience health effects. During
smoke events, it is not uncommon to see AQI
levels of 200 and higher. Under very unhealthy
(AQI 201-300) and hazardous conditions (AQI
301 and higher), EPA and the interagency
Wildfire Guide for Public Health Officials9
recommend all people stay indoors with
filtered air and take additional steps to keep
indoor air clean. Those who are sensitive to
smoke exposure are recommended to relocate
to a cleaner air room. To read more about
recommendations when pollution is
hazardous, see the Reduce Your Smoke
Exposure factsheet10.
Table 2. EPA's Air Quality Index (AQI) levels and PM-driven descriptions.
Air Quality Levels of _ ....
- , , .. . . Recommended Actions
Concern (values of index)
Good (0-50)
Everyone: Don't see or smell smoke? It's a good time to open
windows or go outdoors.
Moderate (51-100)
Everyone: Don't see or smell smoke? It's OKto open windows or go
outdoors.
Unusually Sensitive People: Considermakingoutdooractivities
light and short. Go inside to cleaner air if you have symptoms.
Unhealthy for Sensitive
Groups (101-150)
Everyone: Consider lighter and shorter outdoor activities.
Sensitive Groups: Go inside to cleaner air if you have symptoms.
Unhealthy (151-200)
Everyone: Keep outdoor activities light and short. Go inside to
cleanerairifyou have symptoms.
Sensitive Groups: Consider moving all activities inside. Go inside
to cleaner air if you have symptoms.
Very Unhealthy (201-300)
Everyone: Limit outdoor physical activity. Go inside to cleaner air if
you have symptoms.
Sensitive Groups: Avoid all outdoor physical activity.
Hazardous (301-500)
Everyone: Avoid all outdoor physical activity.
Sensitive Groups: Stay indoors and keep activity levels light.
Stay indoors and considercreatinga cleanerair room.
7 Wildfire Smoke Fact Sheet: At-Risk Groups of People:
https://document.airnow.gov/at-risk-aroups-of-
people-fact-sheet.pdf
8 Air Quality Index: https://www.airnow.gov/aqi/aqi-basics/
9 https://www.airnow.gov/publications/wildfire-
smoke-guide/wildfire-smoke-a-guide-for-public-
health-officials/
10 Reduce Your Smoke Exposure Factsheet:
https://www.airnow.gov/publications/wildfire-guide-
factsheets/reduce-vour-smoke-exposure/
6
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AirNow Fire and Smoke Map
During wildland fire smoke events, detailed and
timely information on outdoor air quality,
active fires, and smoke conditions can be found
on the AirNow Fire and Smoke Map website11
and mobile phone app. The Fire and Smoke
Map allows you to see current PM2.5 air quality
information from permanent and temporary air
quality monitors as well as air sensors; the
locations of fires and smoke plumes; and
recommendations for actions to take to
minimize exposure to smoke from wildland
fires. When clicking on a monitoring location
the map will also alert you if a Smoke Forecast
Outlook has been issued in your area by an Air
Resource Advisor (see Location Alert in
Figure 2), which provides anticipated smoke
concentrations for the next few days.
During wildland fires, employers should pay
close attention to Federal12 and State13
Occupational Safety and Health Administration
(OSHA) recommendations and standards to
protect employees from the effects of air
pollution.
Where Smoke is Likely
Parts of the U.S. are prone to wildfires, such as
California and other western states. However,
other parts of the country may experience
regular prescribed burns or are impacted by
smoke events from distant wildland fires
Smoke can travel hundreds to thousands of
miles under certain weather conditions,
impacting regions far from the fire locations.
For example, in 2023, the eastern U.S. was
inundated by smoke from wildland fires
burning in Canada, which impacted air quality
for weeks.
When Smoke is Likely
Figure 314 shows historical fire activity across
the U.S. during different seasons. Fires impact
every state. Generally, in western states such as
Data Layer Tools
j Adjust the data layers (including the types
VriV of sensors/monitors) shown on the map:
Air Quality
Select the sources of data to show on
the map. Permanent and temporary
(E) Permanent Monitors
monitors are regulatory grade. Air
D Temporary Monitors
sensors are non -regulatory grade and
Air Sensors
the data have been corrected.
Smoke Information
Select whether to show
O NOAA Smoke Plumes
smoke plumes on
0 S plumes reflect smote anynn
tat necessarily near the ground. As
ucn they may net be
the map as gray
mmaM yyteU
7
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Summer
Fall
Legend:
Wildfire
Managed Burns
Figure 3. Seasonal prevalence of wildfire and managed burns across the contiguous United States derived
from the EMBER dataset. Source: Simon et al. 2024.
California and Oregon, wildfire events are most
prevalent between July and October.
Prescribed burns in these states occur mainly in
late fall, followed by winter and spring.
Grassland burns in central states occur in spring
months. In southeastern states, prescribed fires
occur across several months between late fall
and early spring.
When to Prepare for Smoke
If you are in a region known to be impacted by
wildland fire smoke, you should prepare your
building before fire season begins. Those who
may not have a clear fire season should still
prepare in the event that smoke from distant
fires is transported to the region and impacts
air quality. Smoke from wildland fires can travel
thousands of miles from the active fires.
Historical PM 5 concentrations across the U.S.
may be helpful in identifying when your
location is most likely to be impacted by
Where to Get
Information About
Wildland Fire Smoke
During wildland fire smoke
events, refer to the following
sources for timely information
about smoke:
1. AirNow Fire and Smoke Map
website or cell phone app
https://fire.airnow.gov/
2. Smoke outlooks (available on
the Fire and Smoke map)
3. State and local smoke blogs
4. Air Quality Alerts issued by
National Weather Service
(https://weather.gov)
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smoke. EPA provides plots of daily PM2.5 data
across an entire year for locations across the
U.S.: https://www.epa.gov/outdoor-air-qualitv-
data/air-data-tile-plot. Additional historical
PM2.5 data can be found here:
https://tools.airfire.org/historical/ by clicking
on a monitor nearest your location.
The following resources can help you
determine where and when fires are most likely
to occur in the short term:
The National Interagency Coordination
Center Wildland Fire Outlook website is
updated frequently and shows both the 7-
day significant fire potential outlook across
the country and a 4-month prediction of
above-, below-, and near-normal
significant fire potential: https://www.nifc
.gov/nicc/predictive-services/outlooks
Some state or local air agencies are
responsible for issuing permits for
controlled (prescribed) burns, and their
websites may be the best resource for a list
of past and upcoming prescribed fires.
Examples are:
o Arizona: https://smoke.azdeq.gov/
o California: https://ww2.arb.ca.gov/
smoke-current-wildfires
o Montana and Idaho:
https://mi.airshedgroup.org/
o Florida: https://www.fdacs.gov/Forest-
Wildfire/Wildland-Fire/Burn-
Authorizations
o Georgia:
https://georgiafc.firesponse.com/public/
1.3 Smoke Impacts Indoors
During wildland fire events, large amounts of
smoke can infiltrate and accumulate indoors,
leading to elevated air pollutant
concentrations inside buildings. Pollutants,
such as PM and VOCs, are also generated by
indoor activities such as cooking, smoking, and
using wood burning stoves and fireplaces, and
contribute to poor indoor air quality (IAQ).
AQI values are informative for understanding
outdoor air quality, but do not reflect the
concentration of pollutants indoors, which may
be quite different. However, outdoor AQI levels
can help inform when additional measures are
needed to keep indoor air as clean as possible.
Factors that impact IAQ during smoke events
can be grouped into three categories:15
Occupant behavior - the operation and
maintenance of HVAC and additional
filtration (including portable air cleaners,
PACs), opening/closing windows and
doors, and moving between spaces (See
Sections 2, 3, and 4).
Building characteristics - gaps and cracks
around doors and windows, vents, pipes,
and HVAC air intakes. (See Section 3).
Pollutant properties and environmental
factors - particle size, gaseous
component(s), particle concentration, and
wind speed and direction.
The third category is governed by local smoke
properties16 and behavior. This document
focuses on the first two categories, as these
are within building management's control.
15 Luo et al., 2019,
https://www.sciencedirect.com/science/article/pii/SOQ
48969719325276
16 Jaffe et al. 2020,
https://doi.ora/10.1080/10962247.2020.1749731
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Smoke Infiltration Indoors
People spend most of their time in buildings,
especially when outdoor air quality is
poor.15,17,18 During a smoke event, people are
advised to stay indoors and to keep doors and
windows closed. However, not all buildings are
equal in keeping smoke from coming indoors.
Recent studies have shown that some
commercial and school buildings have higher
indoor PM concentrations during smoke events
than residences. However, more studies are
needed to determine if this trend is ubiquitous
across the U.S.19
Smoke infiltrates through open windows and
doors, and cracks, gaps, and other penetration
points in the building envelope (e.g., holes
drilled for lighting fixtures, internet/TV/phone
service cables, or security cameras). Smoke can
also enter a building's ventilation system
through outdoor air intakes (Figure 4). Building
exhausts, such as those in bathrooms and
kitchens, can create negative pressure and
draw in smoke.
1.4 Strategies for
Improving Indoor Air
Quality During Outdoor
Smoke Events
The strategies described in this document are
meant to provide a variety of options to reduce
indoor air pollutant concentrations in non-
residential spaces during smoke events as part
of a Smoke-Ready Plan that is unique for your
building. For residential spaces, see the EPA
Wildfires and Indoor Air Quality website.20 The
Smoke Infiltration Points for Non-Residential and
Multi-Unit Residential Buildings
Gaps and cracks on building
corners and where items are
attached to building facade.
Windows and gaps or
cracks in window seals.
Air intakes for HVAC and
air conditioner units,
and seals around these
units.
Loading dock doors
and seals.
Main door and rooftop access
doors including cracks and
gaps around door jambs.
Air vents and gaps
around vents.
Figure 4. Examples of smoke infiltration points for non-residential and multi-unit residential buildings.
17 Nguyen et al., 2021, https://www.mdpi.com/1660-
4601/18/18/9811
18 Leech et al., 2002,
https://www.nature.com/articles/75002.44
19 May et al., 2021, https://aaqr.ora/articles/aaqr-21 -
03-tn-0046
20 Wildfires and Indoor Air Quality (IAQ):
https://www.epa.gov/emeraencies-iaq/wildfires-and-
indoor-air-qualitv-iaq
10
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most beneficial strategies will depend on
building type, existing infrastructure (such as
HVAC systems or the number of openable
windows and doors), building use, occupant
behavior, and other factors. Not every strategy
will apply to every situation, and it is important
to consult an expert who can evaluate your
building and HVAC system prior to investing in
significant changes. It is also important to
develop your Smoke-Ready Plan well before a
smoke event occurs. Strategies will be provided
throughout this document and an example
Smoke-Ready Plan and checklists are provided
in Appendix 1.
The key strategies discussed further in this
document are:
1. Improvements to HVAC systems and
filtration and modifications to HVAC
settings during smoke episodes.
2. Building usage and weatherization
adjustments, including reducing
indoor sources of air pollution and
adjusting occupant access.
3. Use of Portable Air Cleaners (PACs),
including creating a cleaner air space.
4. Use of air sensors to monitor pollutant
levels inside compared to outside.
11
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2. HVAC Systems: Improvements and
Recommended Settings
BE SMOKE READY
Before a Smoke Event:
Properly maintain your HVAC system.
Determine the highest rated filter your HVAC system can use. Consider upgrading the
system for a MERV13 or higher filter, if needed.
Determine minimum ventilation requirements to develop a "smoke ready mode" and
test the modifications.
Stock necessary filters and supplies.
During a Smoke Event: When smoke is forecast...
I
Install higher-rated filters in your HVAC system.
* Install supplemental filtration.
| Implement Smoke-Ready Plan modifications to your system settings.
After a Smoke Event:
Remove supplemental filters.
Reset HVAC system to normal settings.
Increase building ventilation to fully clear the air.
Change filters and order replacements.
Evaluate and adapt the Smoke-Ready Plan.
This section will be most useful for buildings
with commercial HVAC systems but may also
apply to those with residential HVAC
equipment. Assistance from qualified HVAC
professionals is generally recommended.
HVAC systems vary widely, and their
operational modes are often complex.
Understanding the design limitations, normal
operations, and how to adapt operations
during smoke periods for your unit(s) are
critical parts of a Smoke-Ready Plan. Building
managers should schedule tests prior to
wildfire season and prescribed burn periods to
evaluate optimal air intake settings and ensure
the configurations are effective and switches
between "normal" and "smoke" protocols are
smooth. Retain detailed notes, checklists, and
photos documenting normal operations of the
HVAC system(s), as well as any changes made
during smoke events. This will help build a clear
12
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understanding of effective actions and staff
roles and responsibilities.
Following a smoke event, consider a flush-out
period when the outdoor air intake is increased
to bring in clean outdoor air to replace smoky
indoor air. The HVAC system should be
returned to normal operating procedures, and
building pressure should be verified to ensure
it is typical for normal operation.
2.1 Overview of HVAC
Systems
It is important to understand the different types
of HVAC systems in commercial and residential
buildings.
HVAC systems in commercial buildings can be
categorized depending on their design
features or operation, including (1) centralized,
where a central heating or cooling plant
provides chilled or heated water used to
condition air in multiple buildings or areas (e.g.,
university campus or hospital complex); (2)
decentralized, where each building or area has
its own HVAC system (e.g., window AC units in
a residential system); or (3) a combination of
both. HVAC systems can be designed from
multiple components and 'built up' in a
customized configuration of components or
can be purchased as a single 'packaged
system'. Some common categories for HVAC
systems used in commercial or public buildings
include, but are not limited to:
Rooftop units are self-contained,
packaged HVAC systems that connect to
the building's ductwork and provide
heating, cooling, and filtration. Packaged
units may also be installed near the
building and function similarly to rooftop
installations. These are often used in light
commercial buildings (e.g., strip malls).
Variable Air Volume (VAV) Systems vary air
flow in response to heating and cooling
needs of the space. These systems have
terminal units with some form of flow
control (fan or damper) and potentially
filtration sections to achieve desired
conditions in the space. VAV systems are
often found in commercial buildings.
Variable Refrigerant Flow (VRF) Systems
accomplish heating and cooling with a
variable flow of refrigerant transferring
heat to or from indoors to outdoors. These
systems are larger than mini split systems
(see below) and serve multiple occupied
spaces. They may also include dedicated
outdoor air systems (DOAS), which may
contain a filtration section, to achieve
ventilation requirements (see subsection
on Outdoor Air Intakes for more
information on DOAS).
Mini Split Systems, like VRF systems, use a
refrigerant to transfer heat from the
indoors to outdoors. They either have a
short run duct or are 'ductless,' but
generally condition air in the occupied
spaces and do not bring in outside air and
may not have a filtration section. Window
air conditioning units are similar to ductless
mini splits, but the entire system is
contained in a single package. Mini split
systems are often used in small spaces,
such as offices, shops, and cafes, in a small
area in a building with central HVAC, or in
buildings that only have central heating.
Residential central air conditioning systems
have many components similar to commercial
HVAC systems, including air handlers, heating
and cooling sections, and ducting to deliver
air to occupied spaces and return it to the air
handler. Residential systems may use a or heat
pumps) or may use evaporative coolers (also
called swamp coolers).
13
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Unlike commercial systems, most residential
refrigerant-based air conditioning systems do
not have an outdoor air intake for ventilation
but recycle indoor air with a filtration section
before cycling back through the air handler. A
heat recovery ventilator (HRV) or energy
recovery ventilator (ERV) may provide
ventilation in residential systems, but these are
not common. Evaporative coolers bring in large
amounts of unfiltered outdoor air (see
Modifications to Evaporative Coolers call out
box). Residential systems typically do not run
continuously, but cycle on and off to meet
temperature setpoints.21 These systems are
often used in smaller commercial buildings
(e.g., daycares) or to condition smaller spaces
in larger buildings (e.g., an office in a
warehouse).
HVAC Components and Subsystems
The systems summarized above share many of
the same components and subsystems, which
can directly impact smoke infiltration into the
HVAC system and the ability of the HVAC
system to remove smoke from indoor air. Key
HVAC components, subsystems, and potential
smoke filtration points are shown in Figure 5.
These key components and subsystems use
similar equipment, such as: fans and ducts to
move air, mixing boxes to mix different air
streams, heating and cooling coils (or other
elements) to control air temperature, louvered
intakes or dampers to control flows, diffusers
and return registers to bring air into or out of a
space, filter racks or other in-duct cleaning
technologies (e.g., UV lights) to remove
contaminants from the air, and a variety of
sensors to ensure the system is operating
properly (e.g., pressure, temperature, relative
humidity, CO2, or PM). Overall, there are many
HVAC components and systems that must work
together to achieve thermal comfort and
improve indoor air quality.
Modifications to Evaporative
Coolers
Wildfires often occur during the hottest
months when air conditioning is needed to
keep temperatures comfortable indoors. In
some parts of the country, evaporative coolers
(or "swamp coolers") are commonly used to
cool indoors by bringing in large amounts of
humidified outdoor air. During smoke events,
evaporative coolers can also bring in smoke.
If the indoor air temperature is comfortable,
evaporative coolers should not be used during
smoke events. If cooling is necessary, the
amount of smoke that comes indoors can be
reduced by completely covering the outside
air intakes with a 4-inch-thick filter with a
MERV 13 rating (or better). Because the air will
only pass through the filter a single time,
reducing smoke concentrations by -50
percent, you will also want to use portable air
cleaners to clean your indoor air.
If you cannot cover the outdoor air intakes
with efficient filters, either do not use the
evaporative cooler, or use an air cleaner and
shut off the cooler as soon as your room
reaches a comfortable temperature. Note the
external filters will be vulnerable to damage
from wind, rain, and mist from the cooler and
may need to be replaced frequently.
Examples of swamp coolers with MERV 13 rated
filters attached. Photo credit: FRESSCA Study
Research Team.
21 Touchie and Siegel, 2018, https://doi.Org/10.1111 /ina.12496
14
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Outdoor Air Intakes
Outdoor air intakes are designed to bring
outdoor air into occupied space and can be key
entry points for smoke.
Outdoor air intakes, depending on ventilation
objectives, may have different components and
use different control strategies. All have some
method of controlling the amount of outdoor
air brought inside, often through the use of an
outdoor air damper or an adjustable speed fan.
Dampers may have a fixed position or be
actuated to actively control ventilation.
Actuated dampers are an often-overlooked
component and may malfunction (see callout
box on Common HVAC Maintenance Issues).
Dampers should be inspected prior to smoke
events to ensure they are in good working
order (not warped, stuck in one position, or
otherwise broken). If the damper cannot close
properly, it will not regulate outdoor airflow.
There may also be a separate, uncontrolled
outdoor air intake to maintain a minimum
outdoor air flow to the HVAC while outdoor air
dampers are closed. The outdoor air system
may also have thermal, humidification, and
filtration sections to act on the outdoor air
before mixing it with return air from the
building.
Examples of outdoor air intake systems:
Economizers - Outdoor air economizer
technology saves energy by bringing in
cooler outdoor air to replace warm indoor
air when the outside air is cooler. The
economizer may have a minimum outdoor
air damper position to achieve ventilation
objectives when outdoor air is warmer than
indoor air and may be set to close the
damper if the building is unoccupied.
Demand Control Ventilation (DCV) -
Outdoor air is supplied only when needed,
which can be determined by occupancy or
CO2 sensors. When CO2 concentrations rise
indoors, more outdoor air will be brought
in to ventilate the space. These systems
reduce energy requirements by only
providing ventilation when dictated by
occupancy levels and may be inactive
overnight when buildings are empty.
Dedicated Outdoor Air Systems (DOAS) -
These systems are outdoor air intakes that
include fresh air fans, outdoor air fans, or
make-up air fans that provide a continuous
flow of outdoor air into a building separate
from the HVAC system. A DOAS may be
used in buildings that need additional
makeup air to offset large exhausts (e.g.,
commercial kitchens), that have HVAC
systems with no outdoor air intake (e.g.,
VRF), or to save energy or meet minimum
ventilation requirements.
15
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The Outdoor air intake
allows outdoor air into
the system for adequate
ventilation as controlled
by a damper. May also
include a filtration
section.
The Air handling unit consists of conditioning (heating,
cooling) sections and a supply fan to distribute air
through the system.
Damper
Prefi Iter
Filter
Heating
Cooling
The Air distribution
system is a series of
ducts (may include
fans) that route
conditioned air
through the building.
Dedicated outdoor air systems provide
makeup air from outside to increase
ventilation or maintain building pressure.
Dedicated outdoor
air system (DOAS)
Outdoor
air intake
Exhaust
t .
Exhaust systems release dirty
indoor air directly to the
outside; makeup air from
outside is needed to maintain
building pressure when exhaust
systems are operating.
The Recirculation system
is used to recycle indoor
air into the HVAC system
and may include a
damper, fan, and filtering
sections.
The Terminal unit can be
used to provide a final
stage of condition and
filtration. May have
dampers, heating/cooling,
and filtering sections.
Figure 5. Anatomy of an HVAC system.
16
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Common HVAC Maintenance Issues
A properly functioning HVAC system is helpful in reducing smoke concentrations
indoors. Additionally, components must be functional to make modifications during a
smoke event. Here is a list of common maintenance issues that should be addressed
before smoke events occur:
Filter bypass (i.e., when smoky air gets
around the filter) can be caused by poorly
fitting filters, damaged filters, damaged
gaskets, or damaged filter rack doors.
Broken dampers in the open position can
let in large amounts of smoky air, while
those broken in the closed position can
impact the pressure balance of the HVAC
system and not provide adequate
ventilation.
Leaky seals on dampers can let smoky air
leak through a closed damper.
Leaky ducts can let smoky air into the
HVAC system potentially bypassing
filtration sections.
Broken or uncalibrated sensors can
prevent the HVAC from operating as
designed.
Smoke-Ready HVAC Strategy
Often, a single building may have multiple
types of systems with different components. In
such cases, it is important to understand which
areas of the building are served by each HVAC
system and how each should be adjusted to
reduce wildland fire smoke infiltration and
increase HVAC filtration. The following
information is intended to assist with preparing
and implementing a Smoke-Ready Plan.
Modified HVAC settings should be used as
temporary measures during smoke events
and should be restored to normal operation
when air quality returns to normal. However,
in regions that experience frequent wildfire
smoke (e.g., western states) or those with
prolonged prescribed burn seasons, (e.g.,
southeastern states) it may be more efficient to
make some modifications permanent. More
costly modifications may be made on a
seasonal schedule to coincide with smoke-
prone periods, and easily implemented
changes can be made during smoke episodes
or when air quality alerts are issued.
HVAC system operation changes during a
smoke event may include adjusting settings to
limit outdoor air intake, changing system flows,
and/or changing and supplementing air
filtration. Because HVAC systems vary widely, it
is recommended that you consult an HVAC
professional or your system's manufacturer for
help. A testing, adjusting, and balancing (TAB)
evaluation (See Section 2.4) may also be
useful.
Have your HVAC system serviced to ensure it
is working correctly before you begin testing
smoke settings.
2.2 Air Flow Optimization
During smoke events, reducing the amount of
smoky outdoor air being pulled into a building
is critical for maintaining cleaner air indoors.
However, a lack of ventilation can lead to a
buildup of air pollutants from both indoor and
outdoor sources. Proper ventilation and air
17
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flow are key factors for controlling air
stagnation (e.g., CO2 build up) and maintaining
positive building pressure, which prevents
outdoor air from infiltrating the building.
Reducing outdoor air intake levels to a
minimum, while maintaining positive
pressure relative to the outdoors, can limit
smoke entering the HVAC system. First,
determine the minimum outdoor air intake that
is protective of human health and equipment
by controlling odor, temperature, and indoor
contaminants while maintaining positive
building pressure. The minimum outdoor air
intake is often based on the maximum design
occupancy, but current or anticipated
occupancy levels may be lower and minimum
air intake requirements should be
reconsidered. Closing all outdoor air intakes
completely is never advised.22
Larger HVAC systems and rooftop units are
typically equipped with air intakes to bring
outdoor air into a building. Economizer, DCV,
and DOAS settings in these systems will likely
need to be adjusted to limit the amount of
smoke brought indoors. Modifying these
systems can involve adding control relays or
switches to limit operation, manually adjusting
the air damper position, or finding other
effective modifications. Installing filters on the
air intake is recommended (see Section 2.5).
Due to the variability in manufacturers and
control schemes, there is no one-size-fits-all
solution for settings on outdoor air intakes.
When reducing outdoor air intake, strive to
maintain an overall positive pressure in the
building. Negative building pressure will allow
smoke to be drawn into the building through
cracks around windows and doors as well as
other unintentional openings in the building
envelope. To determine if the building pressure
is positive, you can hold a flutter strip, such as
tissue paper, to the edge or frame of an
external door (see Figure 6 for example).
During a smoke event, perform this check
regularly.
The ASHRAE Epidemic Task
Force Building Readiness
document outlines additional
steps to identify leaks and
other issues in the filter
assembly which should be
addressed (see Common HVAC
Maintenance Issue box).
Negative pressure may occur when there is
insufficient makeup air supplied by the system
to balance airflow lost through an exhaust fan
(e.g., kitchen, bathroom, or laundry room
exhaust vents). Additionally, if it is hot outside
and the outdoor air intake is reduced, a reverse
stack effect can occur, with cold indoor air
flowing out of lower levels and warm outside
air being pulled in through upper levels.
Understanding what impacts building pressure
under normal operation will help optimize
conditions when a smoke event occurs.
When ventilation is reduced, decrease or pause
indoor activities that contribute to poor indoor
air quality, such as spraying aerosols, cooking,
and vacuuming. Using PACs can help improve
indoor air quality if additional filtration is
needed (see Section 4).
protecting-building-occupants-from-smoke-durina-wildfi re-and-prescribed-burn-events?product
18
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if the building pressure is
positive, the strip will flow
outwards
Air is flowing out of
building
Neutral Building Pressure
Flutter strip on the door
frame is hanging
downwards
Smoke-laden air may flow
into building
Negative Building Pressure
Door frame flutter strip is
blowing inwards
Smoke-laden air will flow
into building
Figure 6. Examples of flutter strip test results under different building pressure scenarios.
23 HVAC Run Time
Changes
Indoor air filtration occurs when the fan(s) is
running and filters are placed securely. Some
HVAC systems under normal conditions may be
programmed to turn off at night and on
weekends when the building is unoccupied.
Demand-controlled ventilation systems may
also turn off or reduce flow with changes in
occupancy. In these systems, the HVAC may not
keep indoor air clean during low occupancy
because indoor air does not recirculate
through filters when the HVAC is off. During
smoke events, consider operating the HVAC
system continuously without heating or
cooling (for reduced energy costs) to reduce
smoke even when unoccupied or occupancy is
low. If running the HVAC system continuously
is not viable, consider turning the HVAC system
on before the building is occupied to reduce
smoke indoors.
Building managers should learn how to modify
HVAC run-time and outdoor air intake settings
and practice shifting between normal and
smoke operation before smoke events occur. A
successful test would include:
Maintaining positive building pressure
Maintaining a comfortable indoor
temperature for occupants
Successfully switching between "smoke
ready mode" and normal operation based
on documentation developed in the plan
and/or completed during the test
Document the procedure in your Smoke-
Ready Plan. When a smoke event is forecasted,
switch the system into your smoke-ready
mode, and continue to run it in that mode until
the smoke event ends. During major smoke
events, air quality forecasts can be found on the
AirNow Fire and Smoke Map (see Section 1.2
Smoke Information Sources). After a smoke
event, switch the system back to normal
operations.
19
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2.4 Filtration
Filtration is important to improve indoor air
quality during wildland fire smoke events.
Filters should fit properly in the filter rack
without bending or crushing and there should
not be gaps around the filter frame. Improve
the filter fit with gasketing material, or seal off
gaps with duct tape or silicone sealant.
Not all filters are effective at removing smoke
particles (see MERV Rating Scale box). MERV 8
filters are commonly used in HVAC systems and
need to be upgraded to a higher MERV rating
to effectively remove smoke. MERV 13 or
higher filters are recommended for use
during smoke events as they can remove at
least 50% of the smallest particles (0.3 -
1.0 |jm; the size of most smoke particles) with
each pass through the filter. However, not all
systems can accommodate MERV 13 filters. In
those cases, use the highest rated filter
compatible with the system.
Below are steps to determine the maximum
MERV-rated filter for your system. See pg. 45 of
the ASHFIAE Epidemic Task Force Building
Readiness document for more details.23 While
this document is aimed at airborne infection
control, the MERV-rating evaluation steps are
the same. You may wish to consult a qualified
design professional, certified commissioning
provider (CxP), or certified Testing, Adjusting,
and Balancing (TAB) service provider for larger,
more complex HVAC systems. If you plan to
assess the system yourself, some information
might be available in the most recent TAB
report. If the building has been renovated or
occupancy has significantly changed since the
last report, consider requesting a new TAB
service evaluation. To determine the maximum
MERV-rated filter:
a. Determine the manufacturer, size, thickness,
MERV rating, and pressure drop of the
current filters in use. (see Filter Efficiency
and Pressure Drops callout box for a
description of pressure drop).
b. Identify upgraded filters and their operating
characteristics from the manufacturer, which
may be found in ASHFIAE 52.224 test data.
c. If the higher rated MERV filter has the same
or a lower pressure drop than the current
filter, your system can be upgraded without
modification. Thicker filters can have a low
pressure drop and high MERV ratings, but
they need to fit snugly to effectively reduce
smoke. If the system can accommodate a
MERV 13 filter or higher, install this filter
when smoke is forecast or before seasons
when smoke is likely. If the system is unable
to accommodate a filter of this rating, install
the highest rated filter the system can
handle and operate PACs (see Section 4).
Additionally, if your area is frequently
impacted by smoke, you may consider
upgrading the HVAC system to
accommodate higher rated filters.
23 ASHRAE Epidemic Task Force Building Readiness:
https://www.ashrae.org/file%20librarv/technical%20re
sources/covid-19/ashrae-buildina-readiness.pdf
24
https://www.ashrae.org/File%20Librarv/Technical
%20Resources/CQVID-19/52 2 2017 COVID-
19 20200401.pdf
20
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The MERV Rating Scale and How it Applies to Smoke
Minimum Efficiency Reporting Value (MERV) is
the primary rating system used to indicate how
efficiently a filter removes particles from the
air. The MERV scale is for PM only and is not
used to rate gas-phase pollutant removal.
MERV ratings have different requirements for
various particle size ranges. Wildland fire
smoke is predominantly in the 0.3 - 1 |jm size
range, which is typically the most difficult
particle size to filter from the air.
MERV values vary on a scale from 1 to 16. The
higher the MERV rating of a filter, the more
particles it removes as air passes through.
Other rating systems also exist, including
Micro-particle Performance Rating (MPR) and
Filter Performance Rating (FPR). The
explanation below focuses on MERV as the
industry standard; however, the table below
shows approximate equivalency between filter
rating metrics derived from a study of a limited
subset of filter types.
High-efficiency Particulate Air (HEPA) filters are
another filter rating. HEPA filters are not
typically used in everyday applications for
HVAC and are more commonly used in air
cleaners.
The figure below shows the efficiency with
which different MERV-rated filters remove 0.3 -
1 (jm sized particles from the air.
Average Smoke Removal Efficiency
0.3-1 nm particles
1 - 3 |am particles
MERV 8
MERV 11
MERV13
MPR 600
MPR
1000-1200
MPR
1500-1900
FPR 5
FPR 7
FPR 10
00
>
en
o%
20%
These filters are not effective for smoke.
MERV 8filters are not required to remove 0.3 to 1
(jm particles and only remove
20% of those 1 to 3(jm.
> 20%
fV
65%
MERV 11 filters remove at least 20% of 0.3 to 1(.im
particles and at least 65% of 1 to 3 urn particles
(including PM25from smoke).
CO
r
>
0ฃ
50%
85%
These filters are recommended for smoke.
High-efficiency filters, such as MERV 13, remove at
least 50% of 0.3 to 1nm particles and at least 85%
of 1 to 3 |.im particles (including PM25from smoke).
Data adapted from US EPA " What is a MERV Ratingoriginally derived from a test
method developed by the American Society of Heating, Refrigerating, and Air
Conditioning Engineers (ASHRAE)
For more information on how efficiently MERV-rated filters remove particles from the air, see
EPA: https://www.epa.qov/indoor-air-qualitv-iaa/what-merv-rating.
EPA AirNow: https://www.airnow.gov/sites/default/files/2021-09/wildfire-5moke-guide O.pdf
CARB: https://ww2.arb.ca.gov/resources/fact-sheets/air-cleaning-devices-home
Research: https://doi.org/10.1111/ina.12566
21
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Electrostatic Filters
Many filters with higher MERV ratings use
electrostatically charged fibers to capture small
smoke particles. However, these filters may
become less effective quickly during smoke
events, even at moderate smoke loading (see
the Mechanical vs. Electrostatic Filters
callout box). Although the MERV evaluation
accounts for the effectiveness of a dust-loaded
filter, effectiveness may differ for a smoke-
loaded filter because PM from wildland fires
has characteristics that differ from the dust
used in filter evaluations.
When to Change Filters
During wildiand fire events, filters may
become difficult to obtain, so stock up on
replacements prior to wildfire season and
prescribed burn events. If not already being
used with your HVAC system, install the
selected higher MERV-rated filters when smoke
is forecast Note you may need to change your
filter(s) more frequently during smoke events
depending on the smoke concentration and
event duration, to ensure that the HVAC system
is filtering adequately. Smoke can load filters
quickly and it may be challenging to determine
when a filter has become less effective. If fitted
snuggly in the filter slot, a mechanical filter
loaded with smoke or dust may have an
increased pressure drop across the filter over
time. You can monitor the pressure drop using
a differential pressure sensor as a way to keep
track of filter effectiveness. However, this
approach may not work well with electrostatic
filters, and a visual inspection may be needed.
If filters are very dark or have a strong smoky
odor, the filter likely needs to be changed. For
any filtration approach, air sensor(s) can be
placed in the building to monitor PM
concentration changes over time to help
identify when filters are loaded and are losing
their ability to remove smoke particles. There
are many nuances to using sensor data to
understand if filters have lost their
effectiveness at reducing smoke indoors, See
Section 5 for more in depth discussion on how
to use sensors for assessing wildfire smoke
impacts indoors.
Mechanical vs. Electrostatic Filters
Particle
laden air
Particle
laden air
Mechanical Filters
In mechanical filters, air is forced through filter material,
causing particles to stick to the filter surface. A dense
mat of fibers is required for effective particle removal,
which results in a larger resistance to air flow. This is
measured as pressure drop.
As particles build up on the filter this further reduces
flow through the filter and increases pressure drop.
Electrostatic Filters
In electrostatic filters, also called electret filters, the
filter material is electrostatically charged. This charged
surface attracts charged particles, like a magnet,
removing them from the air. Electrostatic filters require
fewer fibers for effective particle removal and often
have lower pressure drops than equivalent rated
mechanical filters.
Over time some particles, like wildfire smoke, can mask
the charge resulting in electrostatic filters losing their
ability to attract particles to the filter surface.
22
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Following a smoke event, replace filters to
avoid recirculation of odors from dirty filters.
Also consider increasing ventilation (i.e.,
increasing outdoor air intake) when the
outdoor air quality has improved to clear the
air in the building. Restock any filters that were
used during the smoke event.
If power is lost during a smoke event, the ability
to filter the air using the HVAC system is lost. It
may be helpful to create a contingency plan for
power outages.
Sorbents for Gas Removal
Typical MERV 13 and higher-rated filters will
remove smoke-related PM from the air, but not
harmful gas phase species in smoke. Adding
VOC sorbent filters, separate or integrated with
MERV-rated filters, can remove VOCs and some
other gases from the air. The sorbent in these
filters traps gases as air flows through the filter.
Activated carbon is the most widely available
sorbent, but it may not be effective for all gases
in wildland fire smoke. Evaluation standards for
gas removal are not commonly reported by
sorbent filter manufacturers, so picking an
effective sorbent for wildland fire smoke is not
straightforward.
The ASHRAE Handbook provides
comprehensive information on how to design
gas removal components for HVAC systems
and contains more technical details for
removing specific pollutants.25 Helpful metrics
to consider when choosing a sorbent filter
include the:
Type of sorbent. Activated carbon is
recommended for removing many types of
VOCs, but other sorbents like potassium
permanganate more effectively remove
certain harmful compounds in smoke, such
as formaldehyde, acetaldehyde, and
hydrogen cyanide. Multiple-sorbent filters
may more effectively reduce a broad range
of compounds.
Amount and thickness of sorbent in the
filter. More sorbent allows for longer use. A
larger sorbent surface area increases the
efficiency of pollutant gas removal from the
air.
MERV rating. Some sorbent filters are not
MERV-rated, so it is important to determine
if the MERV rating is still met with the
chosen filter. Sorbent-impregnated filter
media may have high MERV ratings and be
effective at removing some gases and PM.
Alternatively, if the HVAC system can
accommodate multiple filters, a sorbent
filter with a low (or no) MERV rating can be
combined with a higher rated MERV filter
to remove particles and gases.
2.5 Supplemental External
Filtration
Additional filtration on outdoor intakes during
wildland fire smoke events may be beneficial.
In addition to higher efficiency MERV filters
within the HVAC system, you can supplement
filtration by attaching additional filters directly
to the outdoor intake.
Your HVAC system may need evaluation from a
professional to determine its ability to
accommodate the additional pressure drop
caused by a temporary supplemental filter
without damaging other equipment.
Filters can be temporarily installed on outside
air intakes using an appropriately sized filter
25 https://www.ashrae.org/file%20librarv/technical%20resources/ashrae%20handbook/i-p a19 ch47.pdf
23
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Filter Efficiency and Pressure Drops
The information in this box relates to mechanical filters. The efficiency of electrostatic
filters may decrease before they experience significant pressure drop. See Section 2.4:
Electrostatic Filters for more information.
A decrease in pressure from one point in a
duct to another is called a pressure drop. This
is a measure of resistance to air passing
through a filter. If there is too much resistance
(too high a pressure drop), the air handling
system works harder to move air, potentially
leading to equipment damage. It is important
to understand how filter characteristics and
particle deposition affect pressure drop in the
HVAC system.
Generally, the higher the filtering efficiency
rating (MERV rating), the higher the pressure
drop. The pressure drop across a filter is also
based on the thickness of the filter, with
thicker filters generally having lower pressure
drop than thinner ones. The pressure drop will
also increase as the filter becomes heavily
loaded with particles.
Ways to minimize the risk of equipment
damage from pressure drop while reducing
smoke concentrations include:
Select the appropriate filter for your
system. The filter needs to have the correct
length, width, and thickness to fit snugly and
have the highest MERV-rating with a pressure
drop suitable for your HVAC system.
Regularly change your filter. Recommended
filter change frequency is between 1 and 6
months, but this may be more often in smoky
conditions. Regular visual checks of the
condition of the filters can aid in setting a
schedule. Generally, if you cannot see the
filter media under the smoke trapped on the
filter or the filter has a noticeable smoke
odor, it needs to be replaced.
Monitor filter pressure drop. If pressure drop
through the filter is reported by your HVAC
system, you need to know the clean filter
pressure drop and the recommended
maximum pressure drop for a heavily loaded
filter. The initial filter pressure drop will vary
by filter type, MERV rating, thickness, and size.
When the pressure drop reaches the
maximum limit, it is time to change the filter.
During smoke events, you may need to rely on
visual inspection or the use of an air sensor
to determine when filters need to be
changed.
Overtime, particle build
up reduces the air flow
through a filter, leading
to a greater pressure
Clean drop across the filter
filter and added strain on the
HVAC system
Dirty
filter
24
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ฎ
with tape or sealant (Figure 7). Consider having
an HVAC professional install permanent filter
racks on the outdoor air intake if you use this
strategy frequently.
If possible:
When smoke is forecast, install the filter
with minimal gaps around the seal/tape.
Perform periodic checks to see when to
change the filter(s), and that seals remain
intact
After a smoke event, remember to remove
the supplemental filter(s) and inspect the
main filter and replace it, if needed. Order
replacement filters for future smoke events.
Figure 7. Images showing additional filters attached
to HVAC air intake. Images from ASHRAE: Planning
Framework for Protecting Commercial Building
Occupants from Smoke During Wildfire Events.
25
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3. Building Usage and Weatherization
Adjustments
BE SMOKE READY
Before a Smoke Event:
Evaluate building for air leaks and repair them.
Check that doors and windows close and seal properly.
Plan adjustments to building entrances to reduce outside air infiltration.
During a Smoke Event: when smoke is forecast...
i
~
For air leaks, implement emergency strategy to seal the leak.
Apply building entrance adjustments.
Run PACs and air curtains (if part of your Smoke-Ready Plan).
After a Smoke Event:
-------
by registered energy experts are available for
residential and commercial buildings and can
identify areas that need sealing. As part of
these audits, building air tightness is tested
using large fans and thermal imagers (also
called thermal cameras). To learn more, reach
out to your local utility company and/or your
local or state government department of
energy or energy commission.
Prior to wildfire season and prescribed burns,
evaluate the building for cracks, leaks, or gaps
around the building exterior and interior.
Places to check on a building's exterior:
Windows
Doors
Vents and fans
Skylights
Siding (especially where siding and other
building features, such as AC units or
chimneys meet)
Exterior building corners
Around window or wall-mounted air
conditioner units
Roof access doors
Loading docks
Service penetrations (e.g., pipes,
plumbing, security cameras)
Places to check on a building's interior:
Windows
Weather stripping around doors
Vents and fans
Baseboards
Electrical and cable outlets
Attic hatches
Fireplace dampers
Around pipes that traverse the ceiling and
or walls
Visual: Visual inspection is a good first step to
help identify certain leaks (Figure 8). For
Figure 8. Example of cracks around
a window and a gap under a door
that may lead to leaks and
infiltration of outdoor air.
example, when indoors, if you can see light
from outside along window or door seals or
wall joints, there is likely a leak.
Leak tests: You can also perform a leak test
prior to a smoke event. Turn off the ventilation
system, fans, and air conditioning. Slowly move
a smoke pen (handheld device that creates a
small mist or smoke stream commonly used for
leak detection) around the edge of the window,
door, or other seals. If at any point the smoke
flows away from the seal, there is likely a leak.
If you can access a thermal imager (Figure 9),
you can use it to identify leaks around windows
and doors by visualizing heat differences.
Thermal imager attachments are also available
for cell phones.
Figure 9. A thermal imager being
used indoors to assess windows
for leaks.
27
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Identify leaks by turning down the ventilation
system, fans, and HVAC inside your building in
winter. Direct the thermal imager at door and
window seals. Leaks will appear as cold spots
(e.g., blues and purples) that indicate cold air
from outside is leaking in. In the summer when
the air outside is warmer, leaks will show up as
warmer spots (e.g., reds, oranges, yellows),
indicating warm air from outside is leaking in.
If a smoke event is already underway and you
have a mobile PM sensor, you can check
window and door seals by holding the sensor
close to the seal. Note that sensors may have a
delay in collecting and displaying the
measurement so it may need to be held in
place for a period of time. If the PM values are
higher closer to the seals when the windows or
doors are closed and were not opened recently
and there are no other nearby sources of PM,
there is likely a leak. This method may not be
helpful in identifying small leaks.
You can also consult a professional to
determine leakage rates at a fixed pressure
across the building. For more on do-it-yourself
(DIY) leak detection and sealing, see the
Department of Energy Detecting Air Leaks
webpage.26
Fix leaks by applying caulking, spray foam,
weatherstripping, or other material to seal
small gaps. Perform repairs where necessary.
During a smoke event, consider emergency
strategies to help seal leaks (i.e., masking tape,
duct tape, or caulking) until a more permanent
fix can be employed after the smoke event has
passed.
3.3 Entrance Adjustments
Adjusting entrance usage during smoke events
may minimize smoky air infiltration when doors
are open. Prior to smoke periods, create a
building plan outlining how to ensure
windows remain closed, which doors will
remain in use, and where PACs will be placed.
Automatic Doors: For buildings with automatic
and manual doors, reduce the use of
automatic doors during smoke events.
Automatic doors stay open longer than needed
and are easily triggered even when not needed.
Manual Doors: Ensure manual doors are closed
when not in use. If entrances have vestibules
with double doors, keep both sets of doors
closed.
Air Curtains: These are powerful vertical
streams of air positioned above doors,
especially those without vestibules (Figure 10)
Air curtains pull recirculated air from inside the
building and create a wall of additional positive
pressure when the door is open. During smoke
events, properly installed air curtains can
provide an air buffer to minimize smoke
infiltration when someone is entering or
exiting the building. Additionally, air curtains
can keep conditioned air inside when doors are
open. Air curtains also keep sight or access
clear, meaning patrons are still easily able to
enter or exit the building as necessary. After a
smoke event, discontinue air curtain use, if
desired.
Figure 10. Example of air curtains
installed above a door frame.
26 https://www.energy.gov/energysaver/detecting-air-
leaks
28
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Limit doors in use: During a smoke event, plan
to limit the use of allowable building entrances
and exits to ones with a vestibule, air curtain, or
revolving door, if available. Consider outdoor
conditions to select doors that are least
impacted by smoke, e.g., those away from the
prevailing winds, for continued use during the
smoke event. Limit the use of other doors when
it is safe and reasonable to do so. Large
entrances such as loading docks can let in large
amounts of smoke.27 Consider limiting their use
to short time periods or after hours when there
are fewer occupants in the building or delaying
deliveries until smoke has passed.
Mitigation near open doors: In some
instances, doors and windows need to be
opened, such as when outdoor temperatures
are hot, and the building is not cooled. In this
case, PACs are most effectively used in the
vicinity of open doors (see Section 4) to
minimize the amount of smoke that enters
deeper into the building.28 Keep in mind, the
filters in these air cleaners may need replacing
more frequently, as they will be drawing in
more polluted air than other units in the
building.
Safety Considerations
When adjusting door usage, always consider
evacuation safety and accessibility to ensure
building occupants can evacuate in case of an
emergency. Instead of locking doors to prevent
use during smoke conditions, place a sign on
the door stating: "Do not use for air quality," or
"Please use other door." This ensures the door
remains operable during an emergency.
Additionally, maintain accessibility and
American Disability Act (ADA) compliance.
After a smoke event, resume full use of
windows or doors.
27 Nguyen, P.D.M., et al., 2021,
https://doi.Org/10.3390/ijerphl 8189811
28 Novoselac and Siegel 2009,
https://doi.Org/10.1016/j.buildenv.2009.03.023
29
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4. Portable Air Cleaners (PACs)
BE SMOKE READY
Before a Smoke Event:
Evaluate the need for PACs.
Select a PAC that removes particles and/or gases, produces little or no ozone, is
Sj'H energy efficient, and meets noise requirements.
For particles, calculate the smoke CADR and number of PAC units needed.
Purchase replacement filters.
During a Smoke Event: When smoke is forecast...
' Deploy PAC unit(s).
Assess PAC effectiveness and replace filters as needed.
ฆ Create a cleaner air room (if part of your Smoke-Ready Plan).
After a Smoke Event:
Change PAC filters and order replacements.
If the PAC removes gases consider running it after PM levels decrease.
Store the PACs for next use.
Evaluate and adapt the PAC section of your Smoke Ready Plan.
4.1 Overview
A PAC is a commercially available standalone
unit that can be plugged into a wall outlet and
moved as needed. These units differ from
HVAC systems as they are not installed on the
roof or walls of a building and serve only the
immediate space around where they are
located. PAC units are not typically designed to
heat or cool a space.
29 Air Cleaners and Air Filters in the Home.
https://www.epa.gov/indoor-air-qualitv-iaq/air-
cleaners-and-air-filters-home
There are many different PACs available.
Although they cannot eliminate all pollutants
from the air, they help improve air quality
indoors when used properly. Some PACs may
remove only particles or only gases, while
others remove both. As wildland fire smoke
contains both particles and gases, an air
cleaner that can reduce one or more pollutants
would be beneficial. U.S. EPA provides detailed
guidance for residential PAC use29. This
30
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document will address larger and commercial
spaces.
Before a smoke event, decide if PACs will be
needed in your building. Create a plan of
where to operate PACs and how many devices
will go in each space. If power is lost during a
smoke event, the ability to filter the air using
PACs is also lost. It may be helpful to create a
contingency plan for power outages.
4.2 When to Use a PAC
There are several scenarios where you may opt
to use PACs to clean indoor air during smoke
events:
Your building does not have an HVAC
system, or your HVAC does not
accommodate MERV 13 rated filters.
The building has areas that need additional
filtration beyond what your HVAC system
can deliver during a smoke event. This
might be determined using an air sensor
(see Section 5 for more information).
You have not yet been able to adjust the
HVAC system settings.
You are setting up a cleaner air room (see
Section 4.7).
Section 4.4 highlights what to consider when
selecting a PAC, including optimal operation,
maintenance considerations, the steps involved
in using a PAC, and additional resources.
30 "Wildfire Smoke, A Guide for Public Health
Officials." https://www.airnow.gov/sites/default
/files/2021 -09/wildfire-smoke-auide O.pdf
31 https://www.epa.aov/ground-level-ozone-
pollution/health-effects-ozone-pollution
If you decide a PAC is helpful for your location
during a smoke event, run the unit at all times
when the building/room is occupied.
If commercial PAC units are unavailable, you
may consider creating a do-it-yourself air
cleaner. For more information, see the DIY Air
Cleaners call out box.
After a smoke event, gases may linger in indoor
air or continue off-gassing from surfaces. Dust
and ash may be resuspended during clean up.
Continue to run your PAC in the cleanup
period. If you have a PAC that also removes
gases, continue to run it after PM levels have
reduced because VOCs may remain elevated
for several days or weeks after a fire.
4.3 Types of Air Cleaners
PAC technology can be categorized based on
the technique used to eliminate pollutants.
Choosing a unit with technology that produces
little to no ozone is very important.30 Ozone is
a harmful gas that can damage lungs when
inhaled.31 The California Air Resources Board
(CARB) provides a list of air cleaners that meet
the California ozone emissions limit.32
Below are the general categories of PAC
technologies used to reduce PM and gaseous
air pollutants.
Particle Removal
1. Mechanical air cleaners pull air through a
filter (either a mechanical filter or an
electrostatic filter) to remove particles, and
do not involve electric fields. Periodically,
the filters will need replacing. PACs using
32 List of CARB-Certified Air Cleaning Devices: https://
ww2.arb.ca.aov/list-carb-certified-air-cleanina-devices
31
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HEPA filters are effective at removing
smoke particles from the air.
2. Electronic air cleaners do not use filters
and instead use electric fields to remove
particles from the air. These devices
include electrostatic precipitators (ESPs)
and ionizers and are not recommended
for smoke removal. Electronic air cleaners
that use oxidants or radicals do not
decrease PM concentrations. 33.H35
Electronic air cleaners that generate ions
can reduce PM concentrations but often
generate harmful ozone or other
byproducts.
Note that a single air cleaner can have both
mechanical and electronic air cleaning
technology. Some allow the user to turn off the
electronic component. In some cases, the order
of the technologies in the air cleaner is
important to reduce potential byproducts
being released back into the room (e.g., fewer
charged particles might be released if a
mechanical filtration component follows an
ionizing component).36
Gaseous Pollutant Removal
Gases and odors can be removed from the air
using certain types of PACs that capture gases
on filter media (such as activated carbon).
Others add gas or odor removal compounds
(such as ozone) to the air to transform gases.
1. Sorbent filters: Some PAC units include
gas removal technologies, such as
activated carbon or alumina coated with
potassium permanganate (an oxidizing
substance that can remove odors and
gases from the air). Ensure you change gas
removal filters regularly, as they can
quickly become ineffective in smoky
conditions.
2. Other gas removal technology:
Sometimes ozone generators are sold for
gas pollutant removal. They produce large
amounts of ozone and should not be
used in schools, homes, or occupied
areas.
Other PAC technologies for removing gaseous
air pollutants are still under investigation and
their effectiveness is unclear, for example:
Air cleaners with high-temperature heating
elements claimed to render contaminants
inactive and remove gaseous pollutants.
Technologies with ultraviolet (UV) bulbs,
plasma, and surface coatings like titanium
dioxide to enhance pollutant removal.
Others may be sold as "hydroxyl"
generators37 or "air washers." These devices
and others also emit ozone and can emit
additional gas-phase pollutants (such as
VOCs). Electronic PAC units that produce
any amount of ozone are not advised.
33 Stinson et al. 2024,
https://doi.org/10.1021/acsestair.3c00083
34 Zeng et al. 2022,
https://doi.ora/10.1016/i.buildenv.2022.108858
35 Zeng et al. 2022,
https://doi.org/10.3390/pollutants2020010
35 Residential Air Cleaners: A Technical Summary:
https://www.epa.gov/sites/default/files/2018-
07/documents/residential air cleaners -
a technical summary 3rd edition.pdf
37 Wildfire Smoke, A Guide for Public Health Officials,
https://www.airnow.gov/sites/default/
files/2021 -09/wildfire-smoke-guide O.pdf
32
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Research has not shown that plasma, heat,
surface coating-technology, or UV light
effectively remove gases in PAC units.38 In some
cases, these technologies may increase
gaseous pollutants present39 and generate
ultrafine particles in the air.40
DIY Air Cleaners
When commercial PACs are unavailable, it is
possible to build a do-it-yourself (DIY) air
cleaner, sometimes called a "box fan filter"
by attaching a furnace filter(s) to the back of
a box fan.
Thicker filters or multiple filters (forming a
triangle or box) increase particle removal by
increasing the filter surface area and
reducing the load on the fan motor.
To ensure the DIY air cleaner is effective:
Use MERV 13 rated filters that are the
same size as the fan (typically 20" x 20").
Attach filters with the air flow arrows on
the filter matching the direction of the
fan.
Use more filters or thicker filters to
increase effectiveness.
Replace filters when dirty or as instructed
by the manufacturer directions.
Many online resources provide instructions,
safety tips, videos, test results, and parts
lists for building a unit, including this
resource from EPA:
https://www.epa.gov/indoor-air-qualitv-
iaq/div-air-cleaner-reduce-wildfire-smoke-
indoors-infographic
Safety Tips
Important safety steps should be followed
when running a DIY air cleaner, including
(but not limited to):
Use only NEWER box fans (manufactured
after 2012) with safety features such as
fused plugs and thermal cutoffs.
Use fans that meet UL 507 or ETL safety
standards and follow the manufacturer
instructions.
Follow manufacturer instructions and do
not use the fan with an extension cord or
leave unattended.
ฉ
B.
LISTED
Intertek
38 https://www.epa.aov/sites/default/files/2018- 40 Link et al, 2024,
07/documents/quide to air cleaners in the home 2n https://doi.ora/10.1021 /acs.est.3c09331
d edition.pdf
39 Ye et al, 2021,
https://doi.ora/10.102.1 /acs.estlett.1 c00773
33
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4.4 How to Select a PAC
Particles, Gases, or Both?
During smoke events, reducing gases in spaces
occupied by individuals with sensitivity to poor
air quality is important
Because no air cleaner is capable of removing
all air pollutants, it is important to check
which gases, VOCs, and particles each PAC
removes. The PAC specification sheet, label, or
manual indicates which pollutants are targeted
for removal. Most PACs state PM removal
capacity (e.g., clean air delivery rate), but have
minimal information on removal effectiveness
for gases or VOCs. A recent study41 suggests an
air cleaner with a large bank of activated
carbon will remove gases and VOCs better than
an air cleaner with a thin activated carbon filter
or additive media such as a hydroxyl generator.
When air quality is very poor (e.g., AQI is in the
Hazardous category), smoke components that
are not effectively removed by air cleaners, like
CO, may cause adverse health effects.
Additionally, at these extreme smoke
concentrations, PACs may not be able to keep
up and keep indoor air clean. At these times,
relocating to a place with better outdoor air
quality may be the best option to reduce
smoke exposure.
Room Size
The most important consideration is sufficient
cleaning capacity for your space. In this section
we consider (1) PACs for smaller spaces (e.g.,
individual offices, classrooms, meeting rooms)
and (2) options for larger spaces (e.g., grocery
stores, libraries, large open offices).
Smaller Spaces and Clean Air Delivery Rate
The Clean Air Delivery Rate (CADR) is a rating
system developed by the Association of Home
Appliance Manufactures (AHAM) to determine
how much air a PAC can filter in a given time
period, and solely applies to particle removal,
not gases. To effectively use PACs, you will
need to calculate the smoke CADR and
number of PAC units needed for your space.
CADR values are typically advertised on PAC
units intended for residential or small non-
industrial settings, and values are reported in
units of cubic feet per minute (CFM) for the
highest fan setting. Be aware that some devices
may report in units of cubic meters per hour
(m3/hr) or no units at all. If you wish to run the
PAC(s) on slower settings (and thus quieter),
more PACs or larger PACs will be required to
reach the desired CADR. Noise considerations
are discussed further in Section 4.5.
Typically, a higher CADR rating indicates a PAC
removes particles faster by moving more air
through the filter and thus is appropriate for a
larger room. CADR is measured separately for
tobacco smoke, dust, and pollen, and the
tobacco smoke CADR is the most appropriate
rating to use for reducing wildland fire smoke.
During smoke episodes, AHAM recommends
selecting an air cleaner with a smoke CADR
that matches your room size in square feet42
(choosing a PAC with a larger CADR will clean
the air faster). For example, an air cleaner with
a smoke CADR of 200 CFM would be
appropriate for a 200 square-foot room with
8-ft ceilings. During non-smoky periods, a PAC
with a tobacco smoke CADR 2/3 the room size
is typically considered sufficient (i.e., CADR of
133 CFM for the previous example).
41 Stinson et al., 2024,
https://doi.org/10.1021/acsestair.3c00083
42 https://www.aham.ora/AHAM/News/Latest News/
Air Cleaner Wildfires.aspx
34
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Table 3. Examples of CADR calculations.
Example of a
room this size
Room area
(square
feet)
Ceiling
height
(ft)
Actual room
volume (ft3)
Equivalent
room area
assuming 8
ft ceiling (ft2)
Number of PACs needed
A single office
room
100
8
800
100
1 at CADR of 100 CFM
Average
conference
room
400
10
4,000
500
1 at a CADR of 500 CFM
2 at a CADR of 250 CFM
Etc.
Average
classroom
800
8
6,400
800
2 at a CADR of 400 CFM
3 at a CADR of 200 CFM
Etc.
Small retail
space
1000
12
12,000
1500
3 at a CADR of 500 CFM
5 at a CADR of 250 CFM
Etc.
Some PAC units note a suggested room size
based on tobacco smoke CADR. You can also
search the AHAM Certified Room Air Cleaner
Directory.43 However, these recommendations
assume a goal of 80% reduction in PM in a
room with an 8-ft ceiling, which may not be
appropriate for commercial and non-
residential spaces. If your ceilings are higher
than 8 feet or if you need greater reduction in
PM concentrations, a higher CADR is needed.
To assess the most appropriately rated PAC for
your room, calculate the minimum CADR rating
using the dimensions of your room. Figure 11
shows how to determine the CADR for your
space with example calculations. The maximum
AHAM verifiable (and therefore certifiable)
smoke CADR rating for PACs is 600 CFM44. If
your calculation results in a CADR greater than
600 CFM, you need to use multiple PACs. As
PAC CADRs are additive45, you can use multiple
units with smaller CADRs to reach the optimal
43AHAM Certified Room Air Cleaner Directory to find
the CADR rating: https://www.ahamdir.com/room-air-
cleaners/
44 ANSI/AH AM AC-1-2020
CADR. An advantage to multiple PACs
distributed throughout large spaces is that they
will help circulate clean air through the room.
Note that the "number of PAC units needed"
column in Table 3 assumes the room has no
additional air filtration, such as an HVAC
system. If you have an HVAC system in place,
you may be able to use fewer PAC units or a
lower fan setting (see Appendix 1 Example
Smoke-Ready Plan for an example of how to
use a staged approach to PAC use with HVAC
to stay ahead of smoke infiltration). The best
way to ensure the combination of HVAC and
PACs is sufficient to clean the air in your space
is to use an air sensor to check indoor pollutant
concentrations (see Section 5).
If you are using a DIY air cleaner, researchers at
EPA have calculated CADR values for different
configurations of fans and filters.46 These are
shown in Table 4.
45 https://www.epa.gov/indoor-air-qualitv-iaq/guide-
air-cleaners-home
45 https://www.epa.gov/air-research/research-div-air-
cleaners-reduce-wildfi re-smoke-indoors
35
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Width: 20 ft
Length: 60 ft
Width: 20 ft
Length: 40 ft
Height: 12 ft
ซ! Jt'.;! ,.,v
e
Height: S ft
. 1 i l**'l
\ ซ: r, i . i iซ
iM*
J P1 Air Cleaner
Air Cleaner
*SfS*ซ
at /
Actual Room Volume = Length x Width x Height
= 60 ft x 20 ft x 12 ft
= 14,400 ft3
Equivalent Room Area = Actual Room Volume + 8 ft
= 14,400 ft3 * 8 ft
= 1,800 ft2
Using an air cleaner with CADR of 600:1,800 ft2 -r 600 = 3
This room would need 3 air cleaners with a CADR of 600
Since the room has 8 ft tall ceilings, we can simply
calculate the area:
Room Area = Length x Width
= 40 ft x 20 ft
= 800 ft2
Using an air cleaner with CADR of 600: 800 ft2 -f- 600 = 1.3
This room would need ~2 air cleaners with a CADR of 600
Figure 11. Example cleaner air space scenarios.
Table 4. CADR values for DIY air
cleaners based on design.
DIY Air Filter Design
Wildfire
smoke
CADR
Box fan with one 1" MERV 13 filter
111 ฑ 1
Box fan with one 1" MERV 13 filter
and cardboard shroud
156 ฑ 4
Box fan with one 4" MERV 13 filter
and cardboard shroud
248 ฑ 15
Box fan with two 1" MERV 13
filters and cardboard shroud
263 ฑ 22
Corsi-Rosenthal Box with four 1"
MERV 13 filters and cardboard
shroud
401 ฑ 31
Air Cleaners for Larger Spaces
For larger facilities, the number of residential
PAC units required to clean the air may be
unreasonable. In this situation, the cost for
many PACs should be compared to the cost to
upgrade the HVAC system or install a new one.
Consider not only the initial price to purchase
PACs but also the ongoing estimated cost to
run them (electricity, filter replacements,
storage, etc.).
Another option for very large spaces is to use
industrial-sized PAC units (e.g., commercial air
scrubbers) often intended for smoke
remediation efforts. The cost of each of unit will
be higher, but the number of units needed for
large spaces will be lower and may result in
lower operating costs (for example, fewer filters
to replace, lower energy costs). Larger units
may also be available to rent Note that these
devices can be quite large, have high airflows,
and may be noisy. In addition, many industrial-
36
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sized, commercial-grade units can be used as
negative air machines by connecting a hose
that exhausts outside. Do not use air scrubbers
as negative air machines during a smoke
event as it could draw in smoke via infiltration.
Industrial air cleaners are classified by their Air
Changes per Hour (ACH), which represents the
number of times per hour the volume of air in
a space is replaced. Unlike CADR, ACH is not a
reliable indicator of air cleaning effectiveness,
so consider using air sensors to verify air
cleaning. Note that some industrial-sized
commercial-grade PACs may report a CADR,
but it will not have been tested to ANSI/AHAM
AC-1 methods. If you do not achieve sufficient
air cleaning based on sensor data, you can
increase the number of industrial PACs in your
space.
4.5 Other Considerations
Cost/Availability
There are a number of costs associated with
PACs that should be considered when selecting
the correct unit for your space, including:
Purchase cost. PACs range from <$100 to
thousands of dollars. Cost can increase if
multiple units are required.
Maintenance cost. This includes
replacement filters, which need to be
replaced more in smoky conditions.
Storage and deployment. Storage for PACs
when not in use and staff time for
deploying units and changing filters
increases expenses.
Filter availability. Replacement filters may be
unavailable for discontinued air cleaners,
requiring a new PAC purchase.
Electricity Consumption
Consider selecting a PAC that is ENERGY STAR
certified. This certification is a U.S. EPA and
Department of Energy designation indicating
the unit meets strict energy efficiency
standards. Models that earn the ENERGY STAR
are independently certified to ensure they save
energy without sacrificing performance, which
means they deliver the same amount of filtered
air as a standard model with less energy.47
Noise
Noise is important to consider because a loud
PAC may cause distractions, discourage
people from occupying a space, or may be
switched off. A balance between acceptable
noise levels for the space and filtration is
important.
Many PACs will list a noise level in decibels (dB)
on their specifications, which can help assess
how loud the unit will sound in a space. Keep
in mind PACs may have different operating fan
speeds, so it is important to know which mode
applies to the listed noise level. The noise level
rating is commonly listed for the low mode,
while the CADR is reported for the high mode,
therefore the unit may be noisier than you
anticipate. Ask the manufacturer or vendor if
this information is not listed on the
specification sheet. Table 5 provides context
for assessing noise levels.
Noise perception will vary based on room size,
sound dampening surfaces, distance from
occupants to the air cleaner, building use (e.g.,
quiet library versus bustling office), variation
(i.e., cycling on and off versus a constant hum),
and pitch. Some noises are viewed as
unacceptable based on the type of noise, even
at low levels. For example, some people find a
47 How to Choose a Room Air Cleaner:
https://www.eneravstar.gov/products/ask-the-
experts/how-choose-room-air-cleaner
37
-------
48
DIY air cleaner operating at 55 dB (the highest
fan setting from 2 feet away) to be distracting "
Table 5. Average (avg.) noise levels of some
common activities to compare to PAC noise
specifications48-5^51
Everyday sounds (distance)
Avg. noise level (dB)
Normal breathing
10
Whisper (5 ft)
20
Dishwasher (next room)
50
Normal conversation (5 ft)
/Air conditioner (100 ft)
60
Vacuum cleaner (10 ft)
70
Garbage disposal (3 ft)
80
Hair dryer (at ear)
82-100
Dog barking (near ear)
110
4.6 Filter Replacement and
Maintenance
PAC maintenance should be performed
according to manufacturer specifications. This
may include cleaning components, replacing
parts, or changing filters. When the PAC is
being used during a smoke event, the filter will
need to be replaced more often than during
times when air quality is good.
Frequent filter replacement may be especially
necessary depending on PAC location. For
example, units in areas where doors/windows
open regularly and allow in polluted outside air
may need replacing more regularly than those
in isolated or enclosed environments without
exterior doors. Ensure you have replacement
filters on hand prior to smoke events.
It is also important to know whether your PAC
includes an alert to tell you when a filter needs
to be changed. Some have an indicator that
changes color based on the air quality, while
others simply have a light that turns on after a
set period of time. Make sure you understand
your unit's alert system before a smoke event.
Also be aware that filter-change indicators may
not function properly under smoky conditions.
if your PAC only has a run time indicator or
does not have an indicator, you should
periodically manually inspect the filter to
determine if it needs changing.
Steps to Check You Filter
1. Compare a photo of a new filter to the one
you remove from the PAC (Figure 12).
Filters with activated charcoal or other
coatings might appear dark to begin with,
so a visual inspection would not be useful
Some PACs contain pre-filters, which
remove large dust particles or pet hair and
may need to be changed more frequently.
SI
IMIIML
1
j i( ! I1
)U
i
05fh
y(ii
Figure 12. Clean (left) and dirty (right) air
filters.
2. Measure PM levels with an air sensor to
determine how effectively air is being
48 Prathibha et al., 2024,
https://doi.ora/10.1016/i.atrnosenv.2024.120650
49 https://www.cdc.aov/nceh/hearina loss/what
noises cause hearing loss.html
50 https://multimedia.3m.com/mws/media/8885530/
noise-navigator- sound-level- hearing-protection-
database.pdf
51 https://www.sandiegocountv.gov/dplu/docs/
081024/TM5499-NOISE-T.pdf
38
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cleaned during smoke events.52 This
technique will help you recognize when
PAC filters need changing (see Section 5).
3. Periodically measure the PAC flow rate.
On most mechanical air filters, the flow
rate through the filter decreases as
particles build up and restrict air flow.
However, electrostatic filters continue to
maintain airflow even after their ability to
filter particles degrades, so it is important
to know what kind of filter you have. To
test flow rate, use a commercially available
flow meter, such as a handheld
anemometer, or set up a flutter strip. A
flutter strip is a piece of light material,
such as tissue paper, taped to the side that
the air is blowing out of on your PAC. As
the flow rate through the filter begins to
decrease, the movement of the flutter
strip and its angle will also decrease. See
Figure 13 for an example.
Also check filters after a smoke episode and
replace dirty filters in preparation for future
smoke events. Some filters will off-gas smoky
odors and gases after smoke events, so you
may need to change them regardless of
appearance.
Evaluate and Adapt
After a smoke event, evaluate how well PAC
units worked by examining air sensor
measurements taken while they were running.
Did they keep the indoor air cleaner? Did they
remain effective over time as they ran? Do you
need to adjust locations or purchase more
units? Note filter loading, the number of high
52 https://www.epa.gov/sites/default/files/2021 -
05/documents/ashrae journal article march 2021-
taaaed.pdf
PM concentration days, and take photos of
dirty filters and clean ones for future reference
and update your Smoke-Ready Plan.
Figure 13. (Left) a PAC with a flutter strip
exhibiting air flow and (Right) reduced airflow
4.7 Creating a "Cleaner Air
Room"
A cleaner air room53 is an isolated space within
a building set up with PACs such that extra-
purified air is available for those at greater risk
from health complications due to smoke. This
category includes children, older adults,
pregnant people, and those with breathing
problems or heart disease. It is important to
remain aware of air quality updates and fire and
smoke movement, as conditions can change
quickly. Follow the AirNow Fire and Smoke
website or app,54 your state or local air quality
agency, or your local news for timely
information on air quality status.
53 U.S. EPA: Create a Clean Room to Protect Indoor Air
Quality During a Wildfire: https://www.epa.gov/
indoor-air-qualitv-iaq/create-clean-room-protect-
indoor-air-qualitv-during-wildfire
54 AirNow Fire and Smoke website:
https://fire.airnow.gov/
39
-------
A cleaner air room is best achieved in buildings
with multiple rooms where one room can be
closed off. For example, an office building can
use a small conference room, a library or
church can use a multipurpose room, and a
daycare can use a playroom. A cleaner air room
may not be possible in establishments like
stores, caii centers, or large warehouses that
typically have one large space with doors that
open outside.
Steps for setting up a cleaner air room:
1. Identify a room large enough to
accommodate the expected occupancy.
2. Keep windows and doors closed to keep
smoke out but maintain clear exits.
3. Keep the space cool. Run fans and air
conditioners that do not pull in outside air.
See the "Heat Caution" callout box.
4. Filter air in the room using a non-ozone-
producing PAC or a DIY air cleaner.
5. Be sure to use one or multiple PACs or DIY
air cleaners with a CADR appropriate for
the room size.
6. Avoid activities in the space that degrade
indoor air quality (i.e., prohibiting smoking
and vaping, reducing or eliminating
cooking, spraying aerosols, burning
candles or incense, sweeping, and
vacuuming - unless the vacuum has a HEPA
filter).
The more time individuals spend in the cleaner
air room, the more benefits they will gain. Be
mindful of changing PAC filters and performing
maintenance when necessary.
Heat Caution
Wildfires frequently occur during the
height of summer when temperatures are
the hottest. As such, there is a significant
risk for heat-related illnesses. In
addition to providing protection from
smoke inhalation, cleaner air spaces
should also prioritize keeping occupants
cool to avoid heat-related health
impacts. This will likely be achieved by
running fans or air conditioning. For
more information, see
CDC Heat Safety page -
https://www.cdc.gov/disasters/extre
meheat/index.html
AirNow Heat and Smoke Fact Sheet -
https:/ / document.airnow.gov/protect-
vourself-from-smoke-and-extreme-
heat.pdf
40
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5. Air Sensors
BE SMOKE READY
Before a Smoke Event:
Assess number and type of sensors needed using sensor selection guidance.
^ Assess need for outdoor sensor(s).
Purchase sensors and accessories.
Consider deploying sensors before smoke events to understand typical conditions.
Till
During a Smoke Event: when smoke is forecast..
Ensure sensors are functional and data are accessible.
If concentrations indoors are increasing:
Compare concentration trends to outdoor trends.
Adjust HVAC settings, filtration, and PAC use as necessary.
Reduce indoor activities contributing to increased concentrations.
Check the building for new leaks.
Check HVAC and PAC filters and replace as needed.
After a Smoke Event:
Perform any required maintenance or cleaning on sensors
Remove and store sensors.
Evaluate and adapt the Smoke-Ready Plan.
5.1 Overview
Some air pollutants can be measured with air
sensors. Air sensors are relatively low cost,
portable, and easy to operate devices that can
provide localized air quality data. They are not
intended to replace the highly accurate
readings taken by regulatory monitors used
by government agencies.
Air sensors can be used to compare pollutant
levels in different locations (e.g., indoors vs.
outdoors, in different rooms) or evaluate trends
in pollutant concentration over time (i.e.,
whether pollutant levels are increasing,
decreasing, or staying the same). During smoke
events, air sensors can identify spaces with
lower pollutant levels and evaluate the
effectiveness of mitigation techniques, such as
HVAC adjustments or PAC usage.
41
-------
Sensors that measure PM2.5 (the primary
pollutant of concern in smoke) are the most
useful for indoor air measurements during
smoke events.55 Though not covered here, CO2
sensors can also be used to ensure adequate
ventilation.
5.2 Choosing an Air Sensor
If you are interested in monitoring pollutants
with air sensors during a smoke event, first
identify the most important sensor
characteristics for your application. This
ensures you (1) choose a sensor that reliably
measures your pollutant(s) of interest during
smoke events; (2) meet needs for data
communication, processing, and display; and
(3) stay within your budget. The questions in
Figure 14 can guide you.56 Purchase sensor(s)
and accessories before smoky periods and
identify where they will be located, how to use
them, and how to access data. Note details in
your Smoke-Ready Plan.
Note that lower-cost sensors are less accurate
than regulatory monitors and may have biases
(e.g., report higher or lower concentrations
than regulatory monitors) or reduced precision.
To guide sensor purchases, U.S. EPA, the Air
Quality Sensor Performance Evaluation Center
(AQ-SPEC), and other organizations conduct
outdoor and laboratory performance
evaluations of some commercially available air
55 Children's Health and Wildfire Smoke Exposure
Work:
https://www.airnow.gov/sites/default/files/2022-
01/chi Idrens-health-wi Idfi re-smoke-workshop-
recommendations.pdf
55 To find your local air district, visit https://www.
airnow.gov/partners/state-and-local-partners/
EPA Sensor loan programs: https://www.epa.gov/air-
sensor-toolbox/air-sensor-loan-programs:
https://www.epa.gov/air-sensor-toolbox/wildfire-
smoke-air-monitoring-response-technology-wsmart-
pilot
sensors.57,58 These assessments are available
for free online and detail accuracy, precision,
bias, and ease of use. Current evaluations do
not cover every low-cost option available.
The U.S. EPA has a website regarding Air
Sensor Technology and Indoor Air Quality,
including information on the performance
metrics of air sensors indoors.59 For monitoring
smoke-related air pollutants indoors, a sensor
reported to have a precision and accuracy
greater than 70% is advisable.60
5.3 Installing Air Sensors
Indoors
There are several important considerations
when choosing where to site a sensor:
Location: Sensor placement is important, and
locations need to be carefully selected.
Figure 15 shows examples of sensor
placement in various environments. Sensors
should be placed in locations representative of
the area where most people are being exposed.
For example, you may consider placing sensors
in the following areas:
Where high risk groups (see Health
Impacts from Smoke in the Introduction)
spend significant time (e.g., daycare, care
facility resident rooms).
57 U.S. EPA Air Sensor Evaluation:
https://www.epa.gov/air-sensor-toolbox/evaluation-
emerging-air-sensor-performance
58 AQ-SPEC: http://www.aqmd.gov/aq-spec
59 U.S. EPA Air Sensor Technology and Indoor Air
Quality: https://www.epa.gov/indoor-air-qualitv-
iaq/air-sensor-technology-and-indoor-air-qualitv
60 U.S. EPA Air Sensor Performance Targets and Testing
Protocols: https://www.epa.gov/air-sensor-toolbox/
air-sensor-performance-targets-and-testing-protocols
42
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Pollutants
Measured
What are my main pollutant
concerns during smoke events?
(Particles? Or Particles and
Gases?)
Sensor Type
MOBILE
STATIONARY
Would a handheld sensor be
useful, or do stationary sensors
make more sense?
Sensor Siting
WIFI CARD CLOUD
Do monitoring locations have
Wi-Fi or reliable cellular service?
Data Visualization
Smq
ON THE
WEB APP
SENSOR
I El (?)
' ฉฉ
How many locations would I
like to monitor?
Sensor Purchase and
Maintenance Costs
MAINTAIN
... , ,t What is the budget to borrow or
Would it be best to view data on . u u
purchase sensors?* How much
the sensor, a computer, or a cell wjH sensor maintenance cost
phone? and who will do it?
Data Privacy
fir 1
Additional Supplies
d~
BATTERY
ACCESS
PRIVATE
EQUIPMENT CABLES
Do monitoring locations have
access to power outlets?
Do I want data uploaded to a
public online platform or to keep
data private?
Do I need cables, mounting
hardware, or other items?
* Check state or local air management districts for available sensor loan programs (see citation in text
for how to find your local air district and EPA air sensor loan programs).
Figure 14. Key considerations when selecting an air sensor.
With the highest occupancy, such as
classrooms, offices with many workers,
congregation space, or on sales floors.
With the greatest foot traffic, such as
hallways, lobbies, or cafeterias.
Within chosen space(s), sensors should be:
Free of obstructions (e.g., large furniture)
that may inhibit airflow to the sensor.
Away from strong air flow (e.g., air vents),
high humidity, and high temperatures
(e.g., radiators, hot water pipes, non-
energy saving lights). If sensors are overly
influenced by airflow from vents, they can
poorly represent indoor air quality.
Protected: Sensors should be placed in
locations where they cannot be tampered
with. This may involve adding caging, or
"camouflaging" the sensor, so it blends in
with the surroundings and draws less
attention (Figure 16).
43
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Indoor Air Sensor Placement Examples
Museum
Sensor located at breathing level in
a frequently-visited exhibit space.
-------
Figure 16. A camouflaged indoor air sensor. The sensor is
hotel lobby where air can flow into and around the sensor,
inside a non-functional lamp shade keeps it out of sight.
Placement: It is best to position indoor air
sensors at or slightly above the average
occupant height Positioning sensors slightly
higher than the average height ensures the air
being breathed is measured by the sensor and
reduces the chances of tampering and
accidental bumps.
Communication: If your sensor requires a Wi-
Fi or cellular connection, make sure the location
chosen has reliable signal strength. Wi-Fi in
public places or schools may require
authentication or input from administration. If
data are stored on an SD card in the sensor,
make sure the installation location allows
access to the card.
Sensors with Displays: Sensors displaying
current PM concentrations can help occupants
However, in larger buildings,
installing multiple stationary
sensors may be advantageous. If
your building has multiple separate
spaces, multiple HVAC systems, or
in populated air cleaning strategies, consider
Placing it installing sensors in key locations to
provide representative air quality
information for different spaces. For
a large space, such as a supermarket, gym, or
place of worship, consider placing one sensor
near the entrance and others where people
congregate.
The number of sensors you place will depend
on the building size, budget available for
sensor purchase, and availability of resources
to monitor data from multiple sensors.
You may find that a portable sensor is helpful
to initially map pollutants in a space to identify
hot spots (i.e., higher-concentration locations)
for permanent sensor placement. Alternatively,
a mobile sensor can survey pollutant
concentrations in different locations. Keep in
mind, the latter approach requires more
attention from the operator. Namely, moving
the sensor during the day to various locations
Sensor Needs: Consider access to power
outlets and any structural support needed for
mounting the sensor. If wall outlets are scarce,
use a power strip or label the plug "do not
unplug" to avoid accidental unplugging. Avoid
using extension cords and long power cord
runs to reduce trip hazards.
identify when air quality conditions indoors are
poor.
Ensure the Sensor is Working: After installation
and when smoke is forecast, ensure the sensor
is working and transmitting data. Look at the
data management system to ensure data are
being transmitted and seem
reasonable.
5.4 Multiple Sensors
Running one air sensor may be
sufficient in small buildings or
where the chosen air sensor is
portable and can easily be moved
from one location to another.
45
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of concern and recording sensor readings and
locations for consistent comparison. Note that
when moving a sensor or using a handheld
sensor, the operator will need to keep the
sensor in place for a period of time (usually at
least a few minutes) for the sensor to accurately
register pollutant concentration in the new
location.
If you plan to use multiple sensors, you should
check the sensors before installing them to
make sure they are performing similarly. This is
often referred to as a "precision check," and is
performed to ensure that when the sensors are
measuring the same air, no one sensor is
measuring much higher or lower values than
expected (bias) compared to the others. Details
on how to perform a precision check are
included in Appendix 4.
If during the precision check the readings from
one sensor consistently differ greatly from the
others, do not show a similar trend (such as
sporadic data spikes), or do not measure at all,
there is an issue with the unit and you should
contact the manufacturer or vendor for repair
or replacement. Once you complete the
precision check and understand the nuances of
your sensors, install them in their permanent
locations.
Periodic precision checks are recommended to
ensure sensors continue to perform as
expected. Precision checking the units at least
once a year prior to smoke season to ensure
they still respond similarly to one another is
advised.
Outdoor Sensor
An outdoor sensor can help inform your
understanding of indoor measurements - if
you note an increasing trend in indoor
concentrations, an outdoor sensor can confirm
the trend is reflective of outdoor conditions. A
note of caution: during smoke events, outdoor
concentrations of pollutants can reach levels
above those that some air sensors are
equipped to measure. This can lead to sensor
overload and the values become unreliable.
This may cause sensors to report errors, stop
responding to concentration changes, or
otherwise malfunction. Using sensors of the
same brand and model of sensor inside and
outside and, through collocation, will facilitate
direct comparison between indoor and
outdoor sensors.
For PM, some air sensors report data at higher
concentrations than measured by regulatory
monitors. As such, EPA and other agencies have
developed correction algorithms to improve
the accuracy of sensor data under a variety of
conditions and concentration ranges. If you
decide to locate a sensor outdoors, you should
familiarize yourself with correction factors that
should be applied to obtain accurate data.
When using an outdoor sensor to compare to
indoor sensor measurements during a smoke
episode, ensure the indoor and outdoor data
have the same correction applied (if one is
applied at all). Be aware that large differences
in relative humidity and temperature
indoors/outdoors may affect data
comparability.
Remember, PM data on the AirNow Fire and
Smoke map61 are accurate even during extreme
smoke events. Sensor data shown on the Fire
and Smoke map have had correction
algorithms applied and do not need to be
further adjusted.
For more information on siting a sensor
outdoors, see the U.S. EPA Guide to Siting and
51 AirNow Fire and Smoke Map:
https://fire.airnow.gov/
46
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Installing Air Sensors62 and Section 4-2 of the
South Coast Air Quality Management District
(South Coast AQMD) Sensor Guidebook.63
If you do not have an outdoor air sensor, you
can use websites that show publicly available
sensor data, such as the AirNow Fire and
Smoke Map61 to find outdoor air quality data.
5.5 Using Air Sensor Data
During a Smoke Event
Air quality data collected indoors should
represent exposure for building occupants.
When smoke is forecast, ensure sensors are
running and data are accessible.
Running your sensor(s) in the months leading
up to wildfire season is strongly
recommended to get an idea of typical indoor
concentrations for your building. This will also
help you identify indoor activities that generate
pollution and may need to be stopped during
a smoke episode to improve indoor air quality.
Sensors may have options for how frequently
they report data, also called the averaging time.
Selecting an averaging time is a balance
between infrequent reporting that will not
capture rapid building responses to filtration
changes (such as reporting hourly) and not
reporting so frequently that the data is erratic
(such as reporting every minute). ASHRAE
guideline 44-2024 suggests 15-minute
intervals provide the most meaningful
estimates.64
Additional Considerations
If you notice an issue with your air sensor, such
as missing data, long periods of zero
concentration, or long periods of the exact
same concentration, your sensor might have an
error. For more information and suggested
action, see Section 4-2 of the South Coast
AQMD Sensor Guidebook65.
After a smoke event, use indoor air sensors to
ensure air quality returns to normal and
document observations and lessons learned
in your Smoke-Ready Plan. Finally, refer to
manufacturer recommendations for
maintenance that may be needed for sensors
after high pollution concentration exposure.
This is especially important if you placed a
sensor outdoors.
62 U.S. EPA Guide to Siting and Installing Air Sensors:
https://www.epa.gov/air-sensor-toolbox/guide-siting-
and-installina-air-sensors
53 South Coast AQMD Sensor Guidebook:
http://www.aqmd.gov/docs/default-source/aq-
spec/star-arant/communitv-in-action-a-
comprehensive-auidebook-on-air-qualitv-sensors.pdf
54 This guideline is available from the ASHRAE Bookstore at
https://store.accuristech.com/ashrae/standards/guideline-44-
2024-protecting-building-occupants-from-smoke-during-
wildfire-and-prescribed-burn-events?product
id=2923808
55 South Coast AQMD Sensor Guidebook: http://
www.aqmd.gov/docs/default-source/aq-spec/star-
grant/communitv-in-action-a-comprehensive-
guidebook-on-air-qualitv-sensors.pdf
47
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Possible Sensor Data Scenarios
Below are scenarios you may encounter when reviewing sensor data during a smoke event. They
are accompanied by suggested checks to determine the cause and recommended actions,
Indoor Concentrations Increasing
Indoor Lags outdoor
There may be several reasons why
indoor concentrations are
increasing. Using an outdoor sensor
for comparison can help you identify
the cause and which actions to take.
ฃ Outdoor Sensor
M/
ArMAA^/^7
indoorSensar'
If indoor data patterns are similar
to outdoor or lag behind, smoke
is entering the building. Consider
enacting your Smoke-Ready Plan,
or adjusting HVAC or PAC settings
if the plan is already in use.
Outdoor constant while indoor increases
Could an indoor source (cooking,
candles, vacuuming} be
contributing to indoor PM? Has a
door or window been left open?
Are HVAC and PAC units working
as expected?
Outdoor Sen&or
Indoor Sensor
y
Short PM25 Increase
ฆ*71
| indoo? Sensor
i Outdoor Sftiisor
V (
Short lived spikes in PM2 5could be caused by indoor
activities such as cooking or cleaning.
Limit indoor activities that can increase concentrations
during smoke events.
Use a PAC to reduce the impact of indoor activities.
Indoor PM2S Sensors Shows Different Trends
Indoor
Sertsor 3
yg
Indoor Seraor 1 \ '
V A.
ฃ Indoor frenspr 2
There are many reasons why indoor concentrations may
vary in different parts of the building
ฆ Is the sensor in an area with higher foot traffic or
frequent door opening?
ฆ Are the different parts of the building served by
different HVAC systems?
ฆ Is a window or door open near the sensor?
ฆ Are indoor activities (e.g. cooking) contributing?
Depending on the cause, you can seek to reduce door openings, deploy PACs in affected
areas, or investigate HVAC settings that may be contributing to increased indoor PMiS.
-------
Indoor PM2,s Remains Higher Than Outdoors
I ndoor Scmsor
v XX
t
Outdoor Sensor
TiiTM? -ป
If the air quality outside has improved, smoke may be
trapped indoors and airing out the building by increasing
the ventilation or opening doors and windows may help
clear smoke out of the building.
5.6 Caveats and Cautions
Despite recent advances, there are still gaps in
our understanding of data quality and sensor
performance indoors. Air sensors do not give a
complete representation of indoor air quality,
as they only detect certain pollutants. Despite
limitations, air sensors are useful informational
tools to support indoor air quality
management during smoke events.
In general, PM sensors require little
maintenance but may drift or malfunction over
time. Gaseous sensors, however, may require
periodic calibration or replacement to ensure
they continue to perform at an acceptable
level. Refer to the manufacturer's manual
and/or the EPA Air Sensor Toolbox66 for
instructions on proper maintenance and
calibration procedures.
There are some limitations of consumer-grade
air sensors that should be considered.
Sensors tend to overpredict (outdoor)
concentrations vs. regulatory-grade
monitors. Adjustment factors for some air
55 EPA Air Sensor Toolbox: https://www.epa.gov/air-
sensor-toolbox
sensors are available from outdoor
studies, but they have not been evaluated
for indoor use. These adjustment factors
are not available for all commercially
available sensors. Currently, there are no
equivalent reference methods or
regulatory grade air monitoring networks
for indoor air.
Air sensor measurements can vary
based on temperature, relative
humidity, and particle type. This
sensitivity to operating conditions can
lead to uncertainty in data quality.67 The
sensor evaluation reports discussed in
Section 5.2 can help you understand
how your chosen sensor will respond
under various conditions.
Sensor performance can vary widely
between different manufacturers'
sensors. When comparing data from
different types of indoor sensors, take
care not to misinterpret data.
67 Nguyen et al., 2021, https://www.mdpi.eom/1660-
4601/18/18/9811
49
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Appendix 1: Building Smoke-Ready Planning
This appendix provides a starting point for developing a Smoke-Ready Plan for your building. Each
section includes an example check list which can be adapted based on your building. In the
checklists not everything will be relevant to your building or more details may need to be made. For
additional detailed information, see ASHRAE Guideline 44-2024, Protecting Building Occupants from
Smoke During Wildfire and Prescribed Burn Events, Section 6.1.
Develop Your Plan
Begin preparations in the off season for wildland fire smoke in your area (see Section 1.2 and
Figure 3). Make a plan on how to prepare your building for smoke. Use the following steps:
1. Predict the building usage during smoke episodes
2. Assess the current state of your building
3. Define the elements of your Smoke-Ready Plan
4. Test your Smoke-Ready Plan
Suggested elements to include in your Smoke-Ready Plan are listed in Table A1.1. For more details
on each, see the associated section in the main text or ASHRAE guideline.
Table A1 1. Elements to include in your Smoke-Ready Plan.
Element
Location of Details
Building Envelope
Measures
Section 3.2 - (Building Use) Sealing the Building
Section 3.3 - (Building Use) Entrance Adjustments
HVAC Measures
Section 2.2 - (HVAC) Air Flow Optimization
Section 2.3 - (HVAC) HVAC Run Time Changes
Pressurization
Measures
Section 2.2 - (HVAC) Air Flow Optimization
ASHRAE 44-2024* Section 5.5.2 Building Controls
Filtration Measures
Section 2.4- (HVAC) Filtration
Section 2.5 - (HVAC) Supplemental External Filtration
Section 4.2 - (PAC) When to Use a PAC
Section 4.3 - (PAC) Types of Air Cleaners
Section 4.5 - (PAC) Other Considerations
ASHRAE 44-2024* Section 5.5.5 - Portable Air Cleaners
Sensing
Section 5.2 - (Air Sensors) Choosing an Air Sensor
Section 5.5 - (Air Sensors) Using Air Sensor Data During a Smoke Event
ASHRAE 44-2024* Section 5.5.1 - Monitoring
ASHRAE 44-2024* Section 6.2.8 - Indoor and Outdoor PM2.5 Monitoring
Logistics/Supply
Considerations
Section 2.4- (HVAC) Filtration
Section 2.5 - (HVAC) Supplemental External Filtration
Section 4.6 - (PAC) Filter Replacement and Maintenance
Section 5.2 - (Air Sensors) Choosing an Air Sensor
* ASHRAE Guideline 44-2024, Protecting Building Occupants from Smoke During Wildfire and Prescribed Burn Events
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1. Predict building usage during smoke episodes
To understand what measures you need in place, assess how the building will be used. Below are
example questions to consider prior to creating a Smoke-Ready Plan checklist:
1. Will all spaces be used?
2. What hours/days will spaces be used?
3. Who will occupy them?
4. How many people?
5. Are any people in at-risk groups?
6. What will they be doing?
7. How could their activities affect IAQ or their exposure to smoke?
2. Assess the current state of your building
Before attempting to create a plan for smoke conditions, you need to know the specifics of your
building filtration and ventilation systems. Example questions to answer include:
1. What kind of filtration measures does the building have in place?
2. Does the building have air conditioning or portable cooling units to maintain comfort levels?
HVAC status questions may be answered with existing building documentation or by meeting with
an HVAC contractor prior to creating a Smoke-Ready Plan.
General
1. What HVAC equipment is in use?
2. Which parts of the building are served by each piece of equipment?
3. Where are the air intakes? Where are the exhausts?
4. Where are the filters? What type of filters are they?
5. Can the unit use MERV 13 filters? If not, what is the highest rating possible?
6. Can you add supplemental filtration to the outdoor air intakes?
HVAC Condition
1. Are damper blades, linkages, and edge seals in good condition (i.e., providing a proper seal)?
2. Are filters undamaged, clean, properly seated, and edges sealed?
3. Do outdoor air dampers function correctly (e.g., open and close on command)?
4. Does the air economizer work correctly?
5. Does the demand control ventilation system work correctly?
Settings
1. What is the minimum outdoor air intake level you need to control odor, temperature, etc. while
maintaining positive pressure?
a. Which exhaust fans are critical for safety? (e.g., isolation rooms, kitchen hoods, hazardous
materials handling)
b. How will you adjust the system to maintain that level?
2. Can some building air handlers be set to full recirculation, while leaving one or a small number of
others still bringing in outdoor air?
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Spaces have been added to the example lists below for customization. Alternatively, create new lists that fit your
unique building situation.
Example Checklist: Smoke-Readv Preparation
Smoke Trigger and Team Roles
~ Determine and document what your trigger level will
be to enter smoke-mode.
~ Define and document roles/responsibilities of the
implementation team.
~ Decide how the plan will be distributed to the team
and how communication will occur.
~
~
~
HVAC Measures
~ Develop smoke-ready settings (with HVAC
contractor, if needed).
~ Practice switching building HVAC to smoke-ready
mode and back to normal mode.
~ Test the HVAC smoke-ready mode with all
adjustments and higher-efficiency filters in place
to ensure it works.
o Document the final implementation process,
o After the test, return to normal operations and
document the process.
~ Stock replacement filters and supplies.
~ Ensure you know how to access filters or that a
contractor is identified to perform potentially
frequent replacements during smoke periods.
~
~
~
Building Measures
~ Walk the building exterior for smoke entry points:
o Exterior doors, windows, vents and fans, skylights,
siding connections with other features (chimneys)
corners, window/wall AC units, and service
penetrations.
~ Walk the building interior for smoke entry points:
o Windows, doors, attic hatches, baseboards,
soffits, electrical outlets, service shafts such as
those for an elevator, and plumbing stacks or
conduits.
o Note any obvious maintenance issues to address
(e.g., cracks or gaps around doors/windows that
can be caulked, broken windows/doors to be
repaired or replaced),
o Note obvious smoke entry points that may be
modified during smoke events (e.g., closing off a
fireplace flue damper or ceasing laundry activities
and closing off the dryer exhaust vents.)
~ Make repairs to minimize leaks
o Caulking around doors/windows, glass panes,
ceiling penetrations, outlets/switches; seal
ductwork; use weatherstripping around moving
openings.
~ Identify doorways that could house air curtains.
~ Identify which windows should be closed.
~ Identify which doors should be closed and which
entrances should remain in use.
~ Identify activities that could be discontinued or
limited to reduce sources of indoor PM.
~
~
~
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Filtration Measures
~ Determine if a cleaner air room is needed and
where it would be located.
~ Determine if PACs are needed and how many are
needed for the space.
~ Determine where to store PACs when not in use.
~ Identify where PAC units will be placed.
~ Purchase PAC units and replacement
filters/supplies.
~
~
~
Sensing Measures
~ Determine if air sensor(s) are needed.
~ Identify where air sensors will be used.
~ Purchase air sensors and practice using the unit,
checking the data, and establish an understanding
of non-smoke concentrations in the building.
~
~
~
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Implement Your Plan
During a smoke event, or when one is forecast, implement your plan guided by your checklist.
Example Checklist: Plan Implementation
HVAC Measures
~ Install higher-efficiency filters.
~ Install supplemental filtration on outdoor air
intake.
~ Adjust air dampers or manually set damper
position.
~ Adjust relief fan airflow.
~ Adjust exhaust fans to reduce air flow.
~ Ensure building is operating at positive pressure.
~ Ensure spaces are conditioned adequately
~
~
~
Building Measures
~ Reduce indoor PM sources.
~ Restrict entrances and window usage, put up signs.
~
~
~
Filtration Measures
~ Deploy PACs to sensitive locations.
~ Establish a cleaner air room if part of
plan.
~
~
~
Sensing Measures
~ Note the PM2.5 levels outdoors (using
the EPA Fire and Smoke Map or an air
sensor) and indoors (with an air sensor)
and monitor throughout the smoke
event to determine if extra filtration
measures are needed.
~
~
~
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After a Smoke Event
Return settings and operations to normal using the checklist.
Example Checklist: Return to Normal Operation
Documentation
Building Measures
~ Use notes/pictures to guide return to normal
~ When building is fully aired out, collect
settings.
PACs and return to storage area.
~ Verify normal operation is accomplished.
~ Inspect PAC filters to determine if
~ Revise Smoke-Ready Plan with lessons learned.
replacements are needed.
~
~ Remove signs restricting entranceways or
window use.
~
~ Clean indoor surfaces as needed.
~
~ Air out building, open doors and windows
HVAC Measures
to allow fresh air in and push out smoky
air.
~ Remove temporary outdoor air filters.
~
~ Inspect and replace filters as needed.
~
~ Reconnect/enable outdoor air dampers.
~
~ Return thermostat to normal settings.
~ Re-enable economizer systems.
Other Considerations
~
~ Stock up on new HVAC and PAC filters.
~
~ Inspect air sensors, if used, and return to
storage.
~
~
~
~
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Example Smoke-Ready Plan
Building Description: Fitness facility inside an older strip mall with wood frame construction and
exterior masonry. Facility is a single story 30,000 ft2 area which consists of an open gym area,
group fitness room, spa, locker room, laundry, and an associated childcare space. There is one
primary entryway with double doors and a vestibule in which almost all the occupants use to
enter and exit. There are two emergency exits that are on the side of the building and are rarely
used. The front of the building is a solid wall of unopenable windows. A view of the building
exterior and schematic floor plan are shown in Figures A1-1 and A1-2.
The space is conditioned by 9 roof top units that serve various parts of the facility. Some units
are dedicated to a single space (e.g. locker room), while other spaces have multiple units that
serve the area (e.g., the gym has two units serving the area). The building is open 24 hours a
day, 7 days a week.
The fitness facility is located in the Western United States, a region that is frequently impacted
by wildfire smoke in the summer and early fall.
In this scenario, the key personnel involved are listed below.
Gym owner - Owns the gym. Hires a facilities manager to control day-to-day facilities issues.
Gym facilities manager - May be a dedicated facilities manager for the gym or could be a staff
member with expanded responsibilities. Responds to day-to-day issues regarding gym facilities.
Is responsible for implementing many of the changes during a smoke event, such as PAC set up,
sensor setup and data retrieval, implementing changes to door usage, and signage.
Building manager - Manages the building on behalf of the building owner. Is responsible for
hiring contractors to fix building issues reported by the gym facilities manager or gym owner on
behalf of the building owner.
Building owner - Owns the building, hires a building manager. May also be responsible for
hiring building contractors.
The following sections are examples of written documents developed collaboratively by the gym
owner, gym facility manager, and the building manager. The document would be used as a
reference for all parties listed above. In the sections below, tasks intended for each key person
are indicated in colored text.
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Figure A1-1 Outside perspective of fitness facility showing rooftop units and roof
fans.
200 ft
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Considerations for Developing a Smoke-Ready Plan
Permissions:
According to the lease agreement, the building manager is responsible for repairs/modifications.
The building manager notifies the building owner and directly hires a contractor to perform
repairs or modifications to the building or HVAC system.
We have agreed that the gym facilities manager will directly contact the building manager
regarding smoke issues, and that the gym facilities manager will also notify the gym owner of
any planned changes.
~ Develop cost estimate for smoke readiness. (Gym owner)
Building Envelope Measures:
~ Since we only have one building entrance, to minimize door use during smoke events, we
will put a sign on the left door to have people only use the right door for entering and
exiting. Will need to acquire signage. (Gym facilities manager)
~ In November, when the outdoor air temperature is cold and indoors is warm, walk around
the inside and outside of the building to identify leaks and note them. (Gym facilities
manager)
o Look for cracks, gaps, etc. in exterior.
o Check indoors around the front and emergency exit doors, electrical outlets, and
laundry room vents for cold air infiltration or daylight shining through cracks,
o Check the wall of windows at the front of the building using our new IR camera to
find leaks around the window frames.
For any issues discovered during the above checks:
~ The building manager has approved us to use caulking as needed. (Gym facilities manager)
~ For other repairs, contact the building manager to hire a contractor. (Building manager)
HVAC Measures:
~ In the winter or early spring (outside of fire season), contact the building manager to hire an
HVAC contractor for a consultation. It may be helpful for both the gym facilities manager
and the building manager to be present during this initial consultation meeting. (Gym
facilities manager / Building manager)
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~ The building manager should communicate with the HVAC contractor that more frequent
HVAC filters replacements will be needed if there is a prolonged or frequent smoke events.
(Building manager)
~ The table below lists what we already know about the building HVAC system, and questions
we need to ask about the system in order to develop a smoke-ready mode. (Gym facilities
manager / Building manager)
1. Known About the HVAC System
2. Items to Discuss with HVAC Contractor
ฆ The locker rooms have dedicated exhaust fans and
dedicated rooftop units (RTU).
ฆ Current thermostat programs are varied to allow
for some HVAC to operate in a continuous
occupied setting while others match the more
frequently occupied building hours 6 am - 9 pm.
ฆ Identify all HVAC and exhaust systems, which
locations they serve, and their normal operation
settings.
ฆ What is the maintenance state of current HVAC
system (evaluate economizer installation and
damper actuator performance).
To help develop a smoke-ready mode:
ฆ Are there any exhausts that are not necessary and
can be sealed off during smoke- e.g., unused dryer
exhaust?
ฆ Can the system handle MERV 13 filters during the
summer and fall- if so, what performance measures
are required (e.g., pressure drop limits)?
ฆ Which RTUs can be put into recirculate mode and
which must maintain outdoor air intake to ensure
positive building pressure?
ฆ Can they help develop control logic for
programmable thermostats to enter into smoke
ready mode.
ฆ How can we make modifications to the childcare
space RTU (sensitive area) to ensure it remains
positively pressurized versus the surroundings?
ฆ How can we ensure we maintain positive pressure
in the doorway vestibule (since it does not have a
dedicated RTU)?
Filtration Measures
~ Identify areas that may need supplemental filtration (childcare space and near the
vestibule). Note, the HVAC system should be providing clean air after it is switched into
smoke-mode, so PAC units will be supplemental. We will use air sensors to determine if
the HVAC system is sufficiently cleaning. If it is not, we will use PACs in the childcare space
and by the front doors as an added filtration measure. In the absence of an HVAC system,
the number of PACs we would need to use are: (Gym facilities manager)
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~ Calculate square footage of the spaces to keep clean.
Dimensions of childcare area = 37 ft (W) x 52 ft (L) x 12 ft (H) = 23,088 ft3.
The equivalent area for a space with 8 ft tall ceilings = 23,088 ft3 -f 8 ft =
2,886 ft2.
Dimensions of the open gym area are approximately = 104 ft(W) x 163 ft (L)
x 14 ft (H)= 16,952 ft3. The equivalent area for a space with 8 ft tall ceilings is
16,952 ft3 - 8 ft =237,328 ft2.
~ Estimate the number of PACs needed for the space.
The number of PAC units with a CADR of 600 needed for the childcare area =
2,886 -f 600 = 4.81, so we would need 5 PAC units for the childcare area.
The number of PAC units with a CADR of 600 needed for the open gym area
= 395.5, so we would need 396 PAC units for the open gym area.
The number of PACs needed for the open gym area is obviously infeasible.
We will implement a staged approach based on the air sensor data:
1. If we discover the HVAC system is not able to keep up with cleaning the
air indoors, we will implement four PAC units in the main gym, and two
in the childcare space.
2. If the PACs are not able to help enough, we will investigate industrial
sized air cleaner(s) for the open gym which provide 1200 cfm of air
movement. Once implemented, we will move the PAC units from the
front vestibule to the childcare space (where an industrial cleaner may
be too noisy to use), so the childcare space has 4 PACs.
~ Estimate the number of filters needed and identify where to purchase. (Gym facilities
manager)
~ Research and purchase PAC units with HEPA filtration that will work for the space (consider
noise level, unit cost, and cost of replacement filters). (Gym owner)
Sensing Measures
~ Ensure thermostat sensors are operating correctly. (Gym facilities manager)
~ Estimate air sensor needs (include considerations for power, Wi-Fi or cellular, connectivity,
and data services plans) and identify potential supplier. (Gym facilities manager)
~ Purchase indoor PM sensors to be used to ensure smoke plan is effective. One will go in the
main gym, and the other will go in the childcare area. (Gym facilities manager)
~ Consider purchasing indoor CO2 sensors to ensure ventilation during smoke mode is
adequate. (Gym owner)
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Implement the Smoke-Ready Plan
Before Smoke Season
Shortly before smoke season, perform the following tasks to prepare for and make pivoting into
smoke-mode more streamlined.
~ Inspect doors and replace weather stripping as needed. (Gym facilities manager)
~ Get the PAC units out of storage and place them in the chosen areas near the front vestibule
and in the childcare area, where they will be used during a smoke event. (Gym facilities
manager)
~ Install air sensors and start using them to capture the non-smoke event PM levels. (Gym
facilities manager)
~ The building manager should schedule an HVAC contractor to install MERV 13 filters.
(Building manager)
Our trigger level: We will enter Smoke-mode when it is smoky outside (there's a visible haze
or it smells like smoke) and the AQI for PM2.5 hits unhealthy for sensitive groups and is
projected to remain elevated for more than a day. To determine the AQI and smoke forecast,
use fire.airnow.gov and local or state smoke blogs or outlooks from air resource advisors
assigned to nearby fires. (Gym facilities manager)
Enter Smoke-Mode
~ Adjust thermostat programming as developed. (Gym facilities manager)
~ Check building pressure is still positive. (Gym facilities manager)
~ Run the PACs near front vestibule and in childcare area. (Gym facilities manager)
~ Put up signs to limit cooking activities in the childcare area. (Gym facilities manager)
~ Review sensor data and adjust plan as needed. (Gym facilities manager)
o If outdoor air is clean, consider opening door to allow fresh air indoors.
~ If smoke persists indoors, re-inspect the building interior and exterior and apply quick fixes
as needed (e.g., new weather stripping, caulking). (Gym facilities manager)
~ If smoke mode is not sufficient to keep indoor air clean, consider acquiring additional PACs
and distribute in day care and then in gym areas. (Gym facilities manager)
~ If a smoke event has been extended, request building manager to contact HVAC contractor
to inspect HVAC filters and replace as needed. (Gym facilities manager)
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Exit Smoke-Mode
~ Adjust thermostat programming back to normal settings. (Gym facilities manager)
~ Consider airing the building out if outdoor air is clean. (Gym facilities manager)
~ Check the building pressure is back to normal. (Gym facilities manager)
~ Inspect PAC filters - identify if replacement filters are needed - store until next smoke
event. (Gym facilities manager)
~ May leave PM sensor to identify indoor air pollution events. (Gym facilities manager)
~ Replace filters as needed. For short smoke duration events and continued fire season you
may leave lightly loaded filters in place. At the end of fire season request the HVAC
contractor return to re-install our normal MERV 8 filters. (Building manager)
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Appendix 2: Resources for Indoor Air Quality
Indoor Air Quality & Airborne Viruses
For additional information about indoor air quality measures, including guidance on infectious
aerosol particles, such as COVID-19 please see:
https://www.ashrae.org/file%20librarv/technical%20resources/covid-19/ashrae-buildinq-
readiness.pdf
https://www.epa.gov/indoor-air-qualitv-iaq
https://www.epa.gov/indoor-air-qualitv-iaq/preventing-spread-respiratorv-viruses-public-
indoor-spaces
https://www.epa.gov/coronavirus/indoor-air-and-coronavirus-covid-19
Smoke Resources
For additional information on smoke, health effects of smoke, and current air quality conditions,
please see:
Current Air Quality Information via AirNow: https://www.airnow.gov/. Additional links on this
page include
o AirNow Fire and Smoke Map (under Fires)
o Be Smoke-Ready Resources (under Fires - Wildfires)
o Air Quality Index Basics
o Wildfire Smoke, a Guide for Public Health Officials (Fires-Wildfires)
Particulate matter general information via U.S. EPA https://www.epa.gov/pm-pollution/.
Additional links on this page include
o PM Basics
o How Smoke from Fires can Affect Your Health
Preparing for Wildland Fire Smoke Webinar Archive: https://www.epa.gov/research-
states/preparing-wildland-fire-smoke-webinar-archive
HVAC Resources
For further resources and more information on HVAC topics, please see:
Protecting Commercial Building Occupants From Smoke During Wildfire Events:
https://www.ashrae.org/File%20Librarv/Technical%20Resources/CQVID-19/Planning-
Framework-for-Protecting-Commercial-Building-Occupants-from-Smoke-During-Wildfire-
Events.pdf
ASHFIAE Guideline 44 - Protecting Building Occupants from Smoke During Wildfire and
Prescribed Burn Events: https://store.accuristech.com/ashrae/standards/guideline-44-2024-
protecting-building-occupants-from-smoke-during-wildfire-and-prescribed-burn-
events?product id=2923808
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Portable Air Cleaners Resources
For further resources and more information on PAC topics, please see:
Wildfire smoke factsheet on indoor air filtration:
https://www.epa.qov/sites/default/files/2018-11/documents/indoor air filtration factsheet-
508.pdf
Air Cleaners and Air Filters in the Home (despite being a resource for residences, this
resource may prove useful in some circumstances for commercial establishments).
https://www.epa.qov/indoor-air-qualitv-iaq/air-cleaners-and-air-filters-home
Determining an appropriate air cleaner for your space: https://www.ahamdir.com/room-
aircleaners
Create a Clean Room to Protect Indoor Air Quality During a Wildfire:
https://www.epa.oov/indoor-air-qualitv-iaq/create-clean-room-protect-indoor-air-qualitv-
durinq-wildfire#how
California Air Resources Board-certified air cleaners list: https://ww2.arb.ca.gov/list-carb-
certified-air-cleaninq-devices
DIY air cleaner safety report: https://chemicalinsiohts.oro/wp-content/uploads/2021/07/DIY-
Box-Fan-Report-2021 .pdf
EPA's research on safety and efficiency of PACs: https://www.epa.gov/air-research/researc h-
div-air-cleaners-reduce-wildfire-smoke-indoors
Air Sensor Resources
For further resources and more information on Air Sensor topics, please see:
U.S. EPA Air Sensor Toolbox: https://www.epa.gov/air-sensor-toolbox/. Additional links and
information on this page include
o Air Sensor Guidebook
o A Guide to Siting and Installing Air Sensors
o Sensor operation and data interpretation
o EPA Sensor Evaluation Results
o EPA sensor loan programs
Community in Action: A Comprehensive Guidebook on Air Quality Sensors:
http://www.aqmd.gov/docs/default-source/aq-spec/star-grant/communitv-in-action-a-
comprehensive-guidebook-on-air-qualitv-sensors.pdf?sfvrsn=10
How to Evaluate Air Sensors for Smoke Monitoring: https://www.epa.gov/research-
states/how-evaluate-air-sensors-smoke-monitoring-webinar-archive
Sensor evaluation and performance via AQ-SPEC: http://www.aqmd.gov/aq-spec
The Enhanced Air Sensor Guidebook: https://www.epa.gov/research-states/enhanced-air-
sensor-guidebook-webinar-archive
EPA's Air Sensor Loan Pilot Programs: Successes, New Resources, and Lessons Learned:
https://www.epa.gov/research-states/epas-air-sensor-loan-pilot-programs-successes-new-
resources-and-lessons-learned
Children's Health and Wildfire Smoke Exposure Work:
https://www.airnow.gov/sites/default/files/2022-01/childrens-health-wildfire-smoke-
workshop-recommendations.pdf
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EPA Air Sensor Technology and Indoor Air Quality: https://www.epa.gov/indoor-air-qualitv-
iaq/air-sensor-technoloqy-and-indoor-air-qualitv
EPA Low-Cost Air Pollution Monitors and Indoor Air Quality: https://www.epa.gov/indoor-air-
qualitv-iaq/low-cost-air-pollution-monitors-and-indoor-air-qualitv
Building Usage and Weatherization Resources
For more information on identifying leaks in buildings, visit:
The Department of Energy: https://www.energy.gov/energysaver/detecting-air-leaks
Additional Resources for Indoor Air Quality
EPA's Indoor Environments Division (IED) provides guidance and programs to help build community
capacity to understand and avoid indoor and outdoor health impacts. Resources available through
https://www.epa.gov/indoor-air-qualitv-iaq/ include:
Indoor Particulate Matter (includes information about National Academies of Science,
Engineering, and Medicine [NASEM] on Indoor PM)
Air Cleaners and Air Filters in the Home
Learn About Wildfires and Indoor Air Quality: https://www.epa.gov/emergencies-iaq/learn-
about-wildfires-and-indoor-air-qualitv
o Wildfires and Indoor Air Quality
o Schools as Cleaner Air and Cooling Centers fact sheets
o Create a Clean Room to Protect Indoor Air Quality During a Wildfire
o Wildfires and Indoor Air Quality in Schools and Commercial Buildings.
Webinar Recordings:
o An Introduction to ASHRAE Guideline 44: Protecting Building Occupants from Smoke
During Wildfire and Prescribed Burn Events, presented by Greg Nilsson, Sarah
Henderson, Abdel Darwich, Mike Gallagher and Randy Cooper. (February 25, 2025)
https://www.voutube.com/watch?v=VLRqqB4RM2M
o Safety and Efficacy of DIY Air Cleaners for Wildfire Smoke Reduction (February 14,
2023) https://www.voutube.com/watch?v=5v6tDspQLXI
o Health Risks of Indoor Exposure to Fine Particulate Matter and Practical Mitigation
Solutions presented by Richard Corsi and Meredith McCormack (April 4, 2024)
National Academies of Sciences, Engineering, and Medicine Resources:
Consensus Study: Health Risks of Indoor Exposures to Fine Particulate Matter and Practical
Mitigation Solutions: https://www.nationalacademies.org/our-work/health-risks-of-indoor-
exposures-to-fine-particulate-matter-and-practical-mitigation-solutions
Indoor Exposure to Fine Particulate Matter and Practical Mitigation Approaches: Proceedings
of a Workshop (2022): https://nap.nationalacademies.org/catalog/26331/indoor-exposure-
to-fine-particulate-matter-and-practical-mitigation-approaches
Health Risks of Indoor Exposure to Particulate Matter: Workshop Summary (2016):
https://nap.nationalacademies.org/catalog/23531/health-risks-of-indoor-exposure-to-
particulate-matter-workshop-summarv
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Environmental Law Institute Resources:
Wildfire Smoke: State Policies for Reducing Indoor Exposure (2024):
https://www.eli.ora/research-report/wildfire-smoke-state-policies-reducina-indoor-exposure
Reducing Indoor Exposure to Particle Pollution from Outdoor Sources: Policies and Programs
for Improving Air Quality in Homes (2020): https://www.eli.org/research-report/reducing-
indoor-exposure-particle-pollution-outdoor-sources-policies-and-proqrams
ASHRAE Resources:
Guideline 44-2024- Protecting Building Occupants from Smoke During Wildfire and
Prescribed Burn Events
Planning Framework for Protecting Commercial Building Occupants from Smoke During
Wildfire Events
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Appendix 3: Glossary of Terms
Term
Activated Carbon
Definition
Porous carbon that adsorbs some types of odors, gases, and vapors.
ACH
AHAM
Air Curtain
Air Handler
Air Changes per Hour. A measure of how many times the air within a room
is replaced each hour.
Association of Home Appliance Manufacturers. A professional
organization that represents the producers of household appliances
including air cleaners.
A controlled stream of air moving across the height and width of an
opening with sufficient velocity and volume to reduce the transfer of air
from one side of the opening to the other and to inhibit insects, dust, and
debris from passing through.
Also called an air handling unit (AHU). This is the part of an HVAC system
that is responsible for regulating and circulating air. It can include an
evaporator coil, blower motor, electric heater package, and other
components. In many cases, it also houses the HVAC filter racks or a filter
chamber.
Air Duct
Air Intake
Airflow
Ambient Air
Conduit used to distribute air in a building.
Device or opening through which outside air is drawn into a building's
HVAC system.
Movement of air, usually within boundaries (such as ducts)
Outdoor air.
ASHRAE
Building Envelope
Professional organization dedicated to advancing the arts and sciences of
heating, ventilation, air conditioning and refrigeration; formerly, the
American Society of Heating, Refrigerating, and Air-Conditioning
Engineers.
Elements of a building that separate the outdoors from the indoors
including walls, windows, doors, roofs, and floors, and the semi-exterior
portions of a building (e.g. unconditioned space).
Clean Air Delivery Rate CADR; The amount of clean air an air cleaner can deliver to a room per
minute. This is often reported in units of cubic feet per minute.
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Cleaner Air Space
An designated space within a building that is set up with air cleaning
equipment to provide cleaner air during a smoke event May also have
cooling equipment to provide heat relief, which may be called a cleaner air
and cooling center.
C02
Carbon dioxide. Can be used as an indicator of ventilation.
Conditioned Space
Part of a building that is temperature and/or humidity controlled for the
comfort of occupants and/or to protect the condition of the space.
Damper
DIY Air Cleaner
A component of an HVAC system that modifies or shuts off airflow.
Sometimes called "box fan filters". DIY air cleaners are made by attaching
one or more HVAC air filters to a box fan using tape, brackets, clamps, or
bungee cords.
Ductwork
Economizer
System of ducts for distribution of air.
Technology that saves energy by bringing in cooler outdoor air to replace
warm indoor air when the outside air is cooler.
Electrostatic Filter
Also called electret filters, the filter material is electrostatically charged.
This charged surface attracts charged particles to the surface, like a
magnet, removing them from the air.
FPR
Filter Performance Rating - a proprietary system similar to MERV
developed by manufacturers to rate filter efficiency.
Heat Recovery Unit
A device that allows for heat recovery ventilation, where residual heat from
an exhaust gas flow is used as a heat source.
HE PA Filter
High Efficiency Particulate Air filter; a mechanical filter that traps particles
by passing air through a fine, pleated, mesh material. HEPA filters are
typically more efficient that MERV 16 filters.
HVAC
IAQ
Infiltration
Heating, ventilation, and air conditioning.
Indoor air quality.
The unintended movement of air from outside of a building inside through
openings in the building envelope.
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MERV
Mechanical Filter
Minimum Efficiency Reporting Value- scale used to rate how well a filter
removes particles from the air. Higher ratings indicate a greater
percentage of particles are captured each time air passes through the
filter. Based on a consensus standard developed by ASHRAE.
In mechanical filters, air is forced through filter material causing particles
to stick to the filter surface.
MPR
Negative building
pressure
PAC
Micro-particle Performance Rating - a proprietary system similar to MERV
developed by manufacturers to rate filter efficiency.
This occurs when the air pressure inside a building is lower than the air
pressure outside the building. This causes air to flow from outside to
inside through open doors and windows, and through cracks and gaps in
the building structure.
Portable Air Cleaner.
Positive Building
Pressure
PM
PMzs
Prescribed Fire
This occurs when the air pressure inside a building is higher than the air
pressure outside the building. This causes air to flow from inside to
outside through open doors and windows, and through cracks and gaps in
the building structure.
Particulate matter.
Fine particulate matter, which are particles with an aerodynamic diameter
generally less than or equal to a nominal 2.5 |jm and are capable of
depositing deep in the lungs.
A planned fire intentionally ignited to meet land management objectives
such as reducing fuel buildup or managing the spread of pests and
disease.
Pressure Drop
Recirculating Air
Register
Return Air
Difference in pressure between two points in a flow system, usually caused
by resistance to air passing through a filter.
Air taken from a space and returned to that space, usually after being
passed through a conditioning system.
Combination grille and damper assembly over an air opening
Device or opening through which air is withdrawn from a conditioned
space (e.g., grills, registers, diffusers, and slots may be used as air inlets).
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South Coast Air Quality (South Coast AQMD) The regulatory agency responsible for improving air
Management District quality for large areas of Los Angeles, Orange, Riverside and San
Bernardino counties, including the Coachella Valley.
SD Card
TAB
Secure Digital (SD) Card - a memory card used to store data in portable
devices, including some types of air sensors.
Testing, Adjusting, and Balancing. A TAB evaluation is performed on HVAC
systems during/after installation to ensure optimized conditions for
occupant comfort, energy efficiency, and indoor air quality. The process
involves measuring and adjusting air flows using test instruments, sensors,
and monitors to ensure appropriate temperatures, airflow, and other
characteristics within the HVAC system.
Thermostat
VAV
Automatic control device used to maintain temperature at a fixed or
adjustable setpoint.
Variable Air Volume System - A type of HVAC system that varies the air
flow in response to the heating and cooling needs of the space.
Ventilation
Vestibule
VOCs
VRF
(1) The process of supplying air to or removing air from a space to control
air contaminant levels, humidity, or temperature within the space. (2) The
process of supplying or removing air by natural or mechanical means to or
from any space. Such air may or may not have been conditioned.
An enclosed space between the inside and outside of a building.
Volatile organic compounds. Carbon-containing gases present in the air.
Variable Refrigeration Flow System - A type of HVAC system where
heating and cooling is accomplished with a variable flow of refrigerant
transferring heat to or from the inside to the outside.
Wildland Fire
Wildfire
An umbrella term for wildfires and prescribed fires.
An unplanned fire caused by lightning or other natural causes, by
accidental (or arson-caused) human ignitions, or by an escaped prescribed
fire.
WUI
Wildland urban interface. This is the space where urban development
meets undeveloped wildlands.
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Appendix 4: How to Perform an Air Sensor
Precision Check
As noted in the main text, if you plan to use multiple sensors, it is recommended that you run a
precision check before installing them in their dedicated locations to make sure they are all
performing similarly. This collocation will ensure that when the sensors are measuring the same air,
no one sensor is measuring higher or lower values than expected (i.e., bias). Only sensors measuring
the same pollutant should be precision checked. For example, if you have selected different sensors
to measure PM and VOCs, then PM sensors should only be compared to PM sensors, and VOC
sensors should only be compared to VOC sensors. Multiple sensors of the same model from the
same manufacturer are expected to vary slightly in reported concentrations and response times to
changes in pollutant concentrations, but large differences indicate a problem.
Guidance on collocation and data interpretation is provided in other documents including these
listed in Appendix 2:
U.S. EPA Air Sensor Toolbox: https://www.epa.qov/air-sensor-toolbox/.
Community in Action: A Comprehensive Guidebook on Air Quality Sensors:
http://www.aqmd.gov/docs/default-source/aq-spec/star-grant/communitv-in-action-a-
comprehensive-guidebook-on-air-qualitv-sensors.pdf?sfvrsn=10
Choosing Your Location
Upon receiving the sensors, choose a location indoors where you can temporarily run them side by
side. For this test, the sensors should be placed about 1 ft apart. See Figure A4-1 for an example setup.
Preparation
Prior to the precision check test, make sure that power is available for the sensors (or the battery is
fully charged); review the users guide or manual on how to start, run, and troubleshoot the sensors;
know (or set) the time interval/reporting frequency of your sensor (1 to 5 minutes is advisable); know
your sensor IDs or names and label them so you can tell the data and sensors apart later; and know
where the data are reported, how to access the data, and how much data is retained.
Run the Precision Test
You should plan to run all sensors simultaneously for at least one day, but longer if possible. This will
allow you to see how the sensors perform under normal operation conditions in your building. You
may wish to introduce a PM source to check that the sensors perform as expected to elevated levels
of PM. Sources might include bringing an extinguished match into the room, or spraying hairspray,
for example.
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Two sets of different sensors are being
compared in this setup. Only sensors of
the same type should be compared to
each other.
Three of four Type 2 sensors agree,
showing all green or with values in a
similar range. One sensor shows orange
and is reading a higher concentration.
In each set of sensors, one sensor
appears to be measuring higher values
than the other sensors. If this persists, a
user could:
Contact the manufacturer for a
replacement
Make note of that specific sensor and
the fact that it consistently measures
higher than the rest, keeping this in
mind when using the sensor in the
building
Figure A4~1. An example set up for how to perform a sensor "precision check" prior to
deploying multiple sensors in a space.
Gather the Data
After your precision test, access the sensor data to evaluate how well the sensors performed. When
reviewing the data, it will be most helpful to look at a time series of the data. A time series shows the
concentration on the y-axis and time on the x-axis. If possible, tiy to look at all sensor data in one
plot as this will help show whether or not the sensors capture the same variation in pollutant
concentrations.
An example time series from a PurpleAir PMy sensor is shown in Figure A4-2. If your chosen sensor
does not provide a time series of the data but instead gives you a list of times and measurements,
you can take the data and create a time series using a program such as Microsoft Excel or Google
Sheets. Tools and data visualizations are discussed the EPA Sensor Toolbox and the South Coast
AQMD Sensor Guidebook.
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Raw PM2.5 ng/m3
70 minute average
Date and Time
Figure A4-2. An example of a time series for comparing sensor data.
How to Evaluate the Data
In your evaluation of the data, there are a few things to look out for such as:
1. Errors: Did any of the sensors fail to report data or report error codes? If so, check the user
manual and/or contact the manufacturer as the sensor may need to be serviced or replaced.
2. Trends: Do the sensors all track concentration in the same way? Is there one sensor that acts
differently than the others? If there is, evaluate why that might be the case; for example, was that
sensor located closer to a door where people frequently come in and out of the room? Was it
located closer to an HVAC vent than the other sensors? If you think a source may have played a
role, try to repeat the precision check test in another location.
If there are no apparent reasons why the sensor was reporting concentrations differently
than the other sensors, you may wish to contact the manufacturer for further assistance.
It is important to remember that multiple sensors will not track perfectly and there will be
variations in the data; however, all sensors should track in the same way. Figure A4-3
shows examples of good and questionable sensor data.
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These 3 sensors show slight differences, but overall
they show the same trends and track each other well
(they increase around the same time as each other
and decrease around the same time as each other).
JE
~3i
on
c
"O
CD
cc
Sensor B
^-Sensor C
"TaH.'J
Id
Time ฆ
Sensor C does not appear to track concentration in
the same way as sensors A and B. This could be
problematic.
Figure A4-3. An example of sensor data that track appropriately (top), and an example where
one sensor is exhibiting problematic behavior (bottom).
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3. Bias: Are there any sensors that consistently report higher or lower concentrations than the other
sensors? This is referred to as bias. Figure A4-4 shows an example of sensor bias. If you find a
sensor is biased, there are two options you could explore. The advised option is to contact the
manufacturer for next steps (they may be able to help you correct the bias or they may suggest
an exchange). Another option is to make note of the sensor exhibiting a bias and to keep in mind
that this one (in the example) is consistently higher than the others. You will need to be mindful
of bias during a smoke event so as not to interpret the space where a biased sensor is as being
more or less polluted than the other spaces. This option is less advisable because real changes in
pollutant concentration will be harder to decipher.
Sensors A and B are relatively consistent with one
another. Sensor C is measuring concentrations
consistently higher than sensors A and B. This high
bias may be problematic and should be addressed.
Figure A4-4. Example showing a sensor reporting data that appear to be biased high.
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