Technical BRIEF
INNOVATIVE RESEARCH FOR A SUSTAINABLE FUTURE
Pressure Washing Surfaces Contaminated with Fixed or
Loose Radioactive Material
Best Practices for Urban Surfaces
Purpose
This technical brief provides a guide for using common
pressure washers and tap water to decontaminate urban
surfaces following a radiological contamination incident.
These urban surfaces include porous, hard surfaces such
as brick, concrete, granite, limestone, and their
composites; non-porous surfaces such as glass, metal, and
painted metal; and semi-porous surfaces such as asphalt.
Vegetation and wood are not addressed. This brief
provides general operating procedures, as well as
estimated time, personnel requirements, and approaches
for minimization and management of generated waste.
Background
The rapid decontamination of high-density urban areas is
critical in the face of a radiological incident, particularly
for contaminants (radionuclides) that have long half-lives,
high-energy gamma emission(s), and/or present an
inhalation or ingestion hazard. Such radionuclides can be
released from dirty bombs, nuclear power plant
accidents, transportations accidents, etc.
Decontamination using readily-available equipment and
resources can help mitigate the consequences of and
expedite recovery from a radiological contamination
incident (e.g., the nuclear power station accident in
Fukushima, Japan). Decontamination by washing can be
performed with equipment found in the inventories of
many governmental agencies, local home supply stores,
and the garages of businesses and homeowners. Many of
these groups and individuals have experience and skill at
using this equipment for various sorts of cleaning
operations, although few, if any, have used it for
radioactive contamination.
For radioactive contamination, the efficacy of pressure
washing depends on the pressure washer configuration
(e.g., pressure rating and the nozzle's spray angle), the
contaminant, the contaminated surface, and the time
between the contamination incident and the pressure
washing. This brief provides operating information based
on reviewed field experience [1] and laboratory
experiments [2-5], While it discusses general safety, this
technical brief does not discuss the safe operation of
pressurized sprayer equipment to avoid physical hazards,
which is typically covered in the user's manual. It also
includes but does not detail issues related to operation of
the equipment to avoid unnecessary exposure of the
equipment operator to radioactivity.
Best Practices for Urban Surfaces
I. General Safety
The operator should avoid being wetted from splashes
and by spray droplets and aerosols reflecting backwards
from the surface. Always don appropriate personal
protective equipment: protective eyewear, face cover,
easily washable or disposable water-repelling clothing
that covers the arms and legs completely, and closed-toe
waterproof shoes. Steel-toe shoes should be worn if the
pressure washer is rated at 4,000 psi or greater. Read the
equipment operator's manual before use and review
additional information provided by the CDC
(https://www.cdc.Rov/disasters/pressurewashersafetv.ht
ml). When equipment is operated appropriately, most of
the spray wiii go forward, away from the operator,
carrying with it the majority of the radioactivity, which is
expected to be in the form of heavy particulates that
present less inhalational hazard. The generation of
reflected spray is greatly reduced if spray operations are
performed under low wind conditions; wind will increase
the spread of potentially contaminated droplets and
aerosols. When necessary to operate under windy
conditions or when spraying areas where excessive
reflection of spray is unavoidable, consider this in the
choice of face cover and/or think about alternatives to
pressure washing.
II. Choice of Wand and Spray Attachments
There are a variety of wand and spray attachments
provided by vendors (Fig. 1). Four primary, common
attachments are the fan nozzle, turbo nozzle, water
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broom, and surface cleaner. Fan nozzles produce a
specified fan pattern that creates a fixed spray angle of 0°,
15°, 20° or 40°. The 0° nozzle is the most powerful for
ablating materials but rarely recommended because it
concentrates the spray into a jet that is difficult to control.
The turbo nozzle (Fig. lb) solves the problem of control
with the 0° nozzle by rapidly rotating the 0° jet in a 25°
cone while retaining the power of the 0° nozzle. The fan
and turbo nozzles generally are not shrouded (covered by
a shroud to control splash aerosol), so caution should be
exercised to minimize reflected splash. The water broom
attachment (Fig. lc) allows for cleaning of a horizontal
surface and/or movement of material to a common
collection area, and some models come with a shroud to
protect the operator against splash and reflected spray
aerosol. To minimize contact with potentially-
contaminated splash aerosol, it is recommended to use a
shroud, if available, that contains the spray. The surface
cleaner attachment (Fig. Id) surrounds the rotating spray
nozzle system with a shroud to minimize aerosol
generation and can be used on horizontal or vertical
surfaces. Some industrial models of pressure washers
have vacuum systems within the shroud that further
minimize the splash and spray aerosol hazard and the
potential for cross-contamination.
Figure 1. Four primary types of pressure washer
attachments: a) standard fan pattern nozzle (spray angle 0°,
15°, 25°, or 40°); b) turbo nozzle; c) water broom
attachment; and d) surface cleaner attachment that
surrounds the rotating spray nozzle system with a shroud to
minimize splash and reflected spray aerosol generation.
Ill, Fixed Contamination Guidelines
Contamination fixed to the surface will require pressures
sufficient to remove or ablate a very thin layer of surface
material to effect decontamination. For horizontal
surfaces, work from the highest elevation toward the
lowest elevation so that the sprayed water moves
downhill, away from the operator. For vertical surfaces,
work from the top toward the bottom. To obtain the
impact pressures on which this technical brief is based
(i.e., the scientific literature cited), it is important to
utilize the appropriate "contact angle" (i.e., the angle
between the wand and the surface) and "spray angle" of
the nozzle discussed earlier (e.g., 0°, 15°). Fig. 2a
illustrates these angles for conventional applications. For
radioactive decontamination, however, the spray nozzle
should be directed as closely as possible to a contact
angle of 90°, although for a freely open (unshrouded)
nozzle, a contact angle of 90° should be avoided to
prevent a significant splash of potentially contaminated
water onto the operator. Instead, for open (unshrouded)
nozzle operation, hold the wand at a contact angle that is
slightly less than 90°. A contact angle of 85° (Fig. 2b) will
significantly reduce splash onto the operator. A contact
angle of less than 75° (Fig. 2c) should be avoided, as the
impact pressure will not achieve the desired cleaning
(ablation) effect. The spray fan pattern should be oriented
parallel to the plane of the user for horizontal surfaces
(Fig. 3a) to ensure a constant contact angle for the spray.
For vertical surfaces, the fan should be oriented vertically,
with the operator moving perpendicular of the fan
direction (Fig. 3b).
Figure 2. a) Example pressure washing system with variables
identified. The power washer flowrate and pressure rating,
nozzle spray angle, the contact angle between the wand and
the surface, and the distance between the nozzle and
surface influence the decontamination efficacy, b) 85° and c)
75° contact angles are shown.
Targeted surface removal is 0.25 mm (0.01"). Based on
experimental data, this can be achieved by holding the
wand no greater than 15 cm (6 in) from the contaminated
surface with a contact angle close to 90° using a 15-
degree nozzle or turbo nozzle. To avoid splash
contamination of the operator, use a contact angle of 85°.
Other nozzle spray angles are not recommended as the
experimental data found poor decontamination at larger
spray angles and longer spray distances [3-5], At the 15
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cm (6 in) distance and with the 15° nozzle, the fan will
cover a width of approximately 4 cm (1.6 in). The nozzle is
moved slowly along the surface at ~0.3 m/min or ~1
ft/min for porous surfaces and ~3 m/min (~10 ft/min) for
non-porous surfaces. These operating conditions are all
important for efficacy, and they are simple to achieve
with practice. The pressure washer should be rated at
least 2,000 psi with a flow rate of at least 4.5 liters per
minute (1.2 gpm). If the 15° or turbo nozzle is not
supplied with the washer, choose a nozzle orifice size
according to the washer manufacturer's instructions.
Figure 3. Orientation of the spray fan and sweep pattern:
horizontal surfaces (left) where the fan plane is as shown,
and movement will be perpendicular to the fan plane;
vertical surfaces (right) where the fan plane is as shown, and
movement will be perpendicular to the fan plane. For turbo
nozzles, the user may move in the forward or left-to-right
directions without regard to the plane. With the surface
cleaner attachment, the user may move in any direction of
both horizontal and vertical surfaces because the spray is
shrouded against splash and spray aerosol.
Water brooms generally do not allow the user to
controllably spray at contact angles greater than 75°.
Therefore, they are not generally suitable for removal of
fixed contamination, unless they can be adjusted to or
operated at the 85° contact angle indicated by
experimental data and have 15° spray angle nozzles.
Surface cleaner attachments have fixed contact angle
nozzles designed to spin the spray bar to generate a large,
circular cleaning pattern. For this system, 15°nozzles
should be installed with a pressure washer rated for at
least 2,000 psi with a flow rate of at least 4.5 liters per
minute (1.2 gpm) to produce the desired ablation. The
surface cleaner attachment should be moved slowly at
around 0.3 m/min (1 ft/min) for porous surfaces and ~3
m/min (~10 ft/min) for non-porous surfaces.
IV. Loose Contamination Guidelines
Contamination ioosely held to or simply sitting on the
surface will require pressures sufficient to move the
material along the surface to effect decontamination. For
horizontal surfaces, work from the highest elevation
toward the lowest elevation, so that the sprayed water
moves downhill, away from the operator. For vertical
surfaces, work from the top toward the bottom. For loose
contamination, the turbo nozzle and the 15°, 25°, or 40°
fan nozzles should be effective. The wand should be held
no more than 27 cm (11 in) from the contaminated
surface with a contact angle close to 90°. To avoid splash
contamination of the operator, use a contact angle of 85°.
These operating conditions are based on experimental
data obtained using a 40° nozzle at a distance no greater
than 28 cm (11 in) [3], which produces a fan width of 23
cm (9.2 in). For other nozzle angles, consult Fig. 4 to
determine an equivalent distance between surface and
nozzle. The nozzle is moved slowly along the surface (~0.3
m/min or 1 ft/min) for porous surfaces and ~3 m/min
(~10 ft/min) for non-porous surfaces. The pressure
washer should be rated for at least 2,000 psi with a flow
rate of at least 4.5 liters per minute (1.2 gpm). If not
supplied with the washer, choose a nozzle orifice size
according to the washer manufacturer's instructions.
Water broom and surface cleaner attachments will be
effective at removing loose contamination and should be
used with a pressure washer rated for at least 2,000 psi
with a flow rate of at least 4.5 liters per minute (1.2 gpm);
and moved slowly along the surface (~0.3 m/min or ~1
ft/min) for porous surfaces and ~3 m/min (~10 ft/min) for
non-porous surfaces. Follow the manufacturer's
instructions for recommended pressure washer rating (psi
and gpm).
Table 1. Recommended power washing parameters for fixed and loose contamination (based on 2,000 psi
and flow rate of at least 4.5 L/min or 1.2 gpm).
Contamination type
Spray attachment type
Maximum distance between
nozzle and surface
Contact angle
Fixed
15° fan and turbo nozzles; surface cleaner
15 cm (6 in)
85°
Loose
15°, 25°, 40° and turbo nozzles, water
28 cm (11 in)*
85°
broom, surface cleaners
*The water broom and surface cleaner attachments have fixed distances and contact angles, but because of the short
distance between nozzle and surface, they remove loose contamination effectively.
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V. Applying Guidelines to Other Washer Configurations
The pressure applied through the washer nozzle is at the
heart of the efficacy of pressure washing. The parameters
in Table 1 are those of the pressure washer used to
generate the experimental efficacy data. To mimic this
experimental set-up, it is recommended that a 40° nozzle
be used at a distance of 28 cm (11 in) for loose
contamination, producing a fan width of 23 cm (9.2 in)
(Figure 4, blue line). However, operators may wish to use
different nozzles or nozzle distances above the surface,
perhaps in conjunction with different spray attachments
(Figure 1). Figure 4 can help users select alternate
configurations. As an example, if the user chooses a 25°
nozzle, the equivalent distance is found by marking the
point where the 40° nozzle line is at 11 in (red dot) and
drawing a vertical line until it meets the 25° nozzle line
(red line). The new distance is 20 in for the 25° nozzle.
For washers with other ratings, to maintain a similar
impact force on the surface, the distance from the nozzle
to the surface needs to change. For washers with higher
ratings than 2,000 psi, the nozzle distance can be
increased and for those rated less than 2000 psi, the
maximum nozzle distance will decrease. Guidelines are
being developed.
-14-12-10 -8 -6 -4 -2 0 2 4 6 8 10 12 14
Fan width (in)
Figure 4. Theoretical coverage for different nozzle fan
angles. This chart can be used to choose an equivalent
nozzle type and distance to the surface for loose
contamination and estimate the application times.
Time and Personnel Estimates
The estimated application times per 100 m2 (~1,100 ft2)
for pressure washing fixed and loose contamination from
U.S. Environmental Protection Agency
porous and non-porous urban surfaces are given in Table
2. The times are represented as person-hours (person-h),
which is one person working for one hour.
Table 2. Approximate application times per 100 m2 (~1,100
ft2) for fixed or loose contamination on porous and non-
porous surfaces [6], The listed person-hrs are only for
pressure washing, not associated activities like waste
management. Additional time for another worker may also
be needed as part of good safety practice.
Contamination
Porous surface
Non-porous surface
type
(1 ft/min)
(10 ft/min)
Fixed
140 person-h
14 person-h
Loose
24 person-h
2.4 person-h
In Table 2, the person-hours for power washing are
estimated to be a factor of ten less for non-porous
surfaces (such as glass, bare or painted metal, painted
and sealed masonry) than porous surfaces (such as
concrete, brick, other masonry) because of the larger fan
pattern necessary [3]. Higher rates were also reported for
loose contamination with simulated fallout particles by
another washing approach [4]. Assuming non-porous
surfaces are smooth and contaminants cannot seep into
the subsurface, all contaminant forms will be quickly
removed from non-porous materials. Asphalt, while it is
generally non-porous unless cracked or aged, can have
fixed contamination if its aggregate is exposed and
porous. Thus, materials that are essentially only slightly
porous, such as asphalt, can be cleaned at a faster rate
using a 15° nozzle held no greater than 15 cm (6 in) from
the contaminated surface and moved at a faster rate of
~3 m/min (~10 ft/min) than suggested in Table 2 for
porous surfaces.
The application time is influenced by the choice of spray
nozzle and height, which can vary by spray attachment
(Fig. 1). Figure 4 can be used to estimate application time.
To do this, the operator first finds the fan width for their
nozzle type (for the turbo nozzle, use the 25° line) and
distance. The total contaminated surface area is
calculated by multiplying the area's width by its height,
and then this value is divided by the product of the
movement rate and the fan width. For example, a 10m x
10m (32.8 ft x 32.8 ft) wall has a surface area of 100m2
(1,100 ft2). For loose contamination, the operator decides
to use a 25° nozzle from the example in Section 5 that
produces a fan width of 23 cm (9.2 in). Because the
recommended movement rate is 0.3 m/min (1 ft/min),
the calculated application time is:
100 m2
¦ = 1449 min =24 h
0.23m x 0.3-
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Waste Management
Decontamination will produce solid and/or liquid waste,
depending on the contaminant and contaminated
surface. Prepare to capture and store any waste liquid
and debris from washing activities until guidance from
local, responsible authorities on the management of such
waste is determined. Additional information about
equipment for waste management can be found
elsewhere [7, 8]. The amount of liquid waste generated
by pressure washing can be estimated by multiplying the
rated pressure washer flow rate and the application time.
If the application time is not pre-established, it can be
estimated via Fig. 4, as described above using the nozzle
degree, distance between the nozzle and contaminated
surface, and the wand movement rate.
Additional Challenges and Concerns
There are challenges related to the use of pressure
washing for contaminant removal not fully considered in
this brief. One is the reabsorption of contaminants onto
surfaces after pressure washing, particularly runoff from
higher surfaces contaminating lower surfaces.
Reabsorption is mainly a concern for contaminants in the
liquid phase of the waste/runoff. Relatedly, particles may
become forced into cracks in the surface at the site of
pressure washing, or particles in the runoff water may
become trapped in downstream cracks. Another
consideration arises from filtering and collecting the solid
waste generated from power washing contaminated
surfaces; this affects both dose accumulation from
collected solids and the deployment of such a system at
field scale. For pressure washing activities occurring after
a large contamination incident, acceptable work periods
based on projected dose can vary. Lower-level areas
would not be expected to produce doses that would limit
working times [7], but pressure washing in higher
radiation zones may require limited work periods to limit
dose to personnel. Also, one must consider that
personnel may need to stand much closer to
contaminated surfaces for fixed contamination pressure
washing than for loose contamination pressure washing,
thus incurring higher dose.
Contacts
Technical Contacts
• Matthew Magnuson, magnuson.matthew@epa.gov
• Michael Kaminski, kaminski@anl.gov
• Katherine Hepler, khepler@anl.gov
General Feedback/Questions Contact
• CESER@epa.gov
U.S. Environmental Protection Agency
Disclaimer: This technical brief is for informational purposes
only. It was subject to administrative review but does not
necessarily reflect the view of the U.S. Environmental
Protection Agency (EPA). No official endorsement should be
inferred, as the EPA does not endorse the purchase or sale of
any commercial products or services. The submitted technical
brief has been created by UChicago Argonne, LLC, Operator of
Argonne National Laboratory ("Argonne"). Argonne, a U.S.
Department of Energy Office of Science laboratory, is
operated under Contract No. DE-AC02-06CH11357. The U.S.
Government retains for itself, and others acting on its behalf,
a paid-up nonexclusive, irrevocable worldwide license in said
article to reproduce, prepare derivative works, distribute
copies to the public, and perform publicly and display publicly,
by or on behalf of the Government. All figures are courtesy of
Shutterstock or not subject to license.
References
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decontamination in an urban environment after radiological
dispersion: A review and perspectives. J. Haz.Mat., Vol. 305, pp. 67-
86, 2015.
2) W. C. Jolin, M. L. Magnuson, and M. D. Kaminski. High Pressure
Decontamination of Building Materials during Radiological Incident
Recovery. J. Environ. Radioact., p. 105858, Jun. 2019.
3) K. Hepler, M. D. Kaminski, W. Jolin, and M. Magnuson.
Decontamination of Urban Surfaces Contaminated with Radioactive
Materials and Consequent Onsite Recycling of the Waste Water.
Environ. Technol. Innov., p. 101177, 2021.
4) W. Jolin and M.D. Kaminski. Developing surrogate far-field
nuclear fallout and its rapid decontamination from aircraft surfaces.
ANL/SSS-19/1, 2019. https://doi.ore/10.2172/1543295.
5) M.D. Kaminski, C. Oster, N. Kivenas, S. Lopykinski, and M.
Magnuson. Penetration of Fission Products Ions into Complex Solids
and the Effect of Ionic Wash Methods. Environ Sci. Pollut. Res., 28,
10114-10124, 2021. https://doi.org/10.1007/sll356-02Q-11392-w.
6) W. Jolin, M.D. Kaminski, K. Hepler, and M. Magnuson. Detailed
Guidelines for the Decontamination of Porous and Non-Porous
Surfaces from Radioactive Contaminations. In preparation.
7) M.D. Kaminski, K. McConkey, M. Magnuson, and S.D. Lee.
Municipal and commercial equipment for radiological response and
recovery in an urban environment: State of science, research
needs, and evaluation of implementation towards critical
infrastructure resilience. ANL-NE-17-37, 2017.
https://doi.ore/10.2172/1528921.
8) M. Magnuson and M.D. Kaminski. Readily Available Equipment
for Response and Recovery. U.S. EPA Emergency Response
Research Webinar Series, 2021. https://www.epa.gov/emergencv-
response-research/readilv-available-equipment-response-and-
recoverv-webinar.
9) M.D. Kaminski, K. Sanders, M. Magnuson, K. Hepler, and J.
Slagley. External Dose to Recovery Teams Following a Nuclear or
Radiological Release Event. Health Physics, 120(6), pp. 591-599,
June 2021. https://doi.org/10.1097/hp.00000000000Q1381.
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