United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park, NC 27711
Research and Development
EPA/600/SR-93/027 April 1993
EPA Project Summary
Reference Manual for RASSMIT
Version 2.1: A Sub-slab
Depressurization System Design
Performance Simulation
Program
David E. Hintenlang
A computer program has been de-
veloped to simulate and aid in the de-
sign of sub-slab depressurlzation
systems used for indoor radon mitiga-
tion. The program has been designed
to run on DOS-compatible personal
computers to ensure broad applicabil-
ity as a design tool for these mitigation
systems. The program addresses both
major techniques for employing sub-
slab depressurization in slab-on-grade
construction: discrete suction pits and
extended suction systems. Discrete pit
suction systems are applicable to both
retrofit mitigation systems in existing
houses and new house construction.
Extended suction systems use some
form of highly porous material, most
typically drainage mat or large aggre-
gate, to extend the suction over large
distances below concrete slabs. These
systems must be installed prior to pour-
ing the slab and are therefore appli-
cable only to new house construction.
The RASSMIT computer program pro-
vides a menu-driven scheme to design
and evaluate these indoor radon miti-
gation systems for houses utilizing
slab-on-grade construction techniques
over low permeability soil and fill mate-
rials.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Research
Triangle Park, NC, to announce key find-
Ings of the research project that Is fully
documented In a separate report of the
same title (see Project Report ordering
Information at back).
Overview
The program utilizes finite difference
techniques to provide numerical solutions
to the differential equations that describe
the airflow through the sub-slab volume.
Following the user's specification of the
parameters describing the building slab
and mitigation system, three-dimensional
solutions for the pressure and velocity
fields in the sub-slab volume are obtained.
The results have been well verified on full-
size test slabs and for a number of houses
where sub-slab depressurization systems
have been installed.
Program operation is straightforward and
menu-driven. The user steps through a
series of screens where prompts for input
solicit specification of the mitigation sys-
tem. The program documentation provides
a reference to the overall design and op-
eration of the program. It also provides
explicit descriptions and explanations for
each input parameter. This provides the
user with enough information to select a
reasonable value for each input param-
eter for a particular application, or pro-
vides default values representative of
conditions found in Florida houses. Help
screens are also provided for each input
parameter and provide an on-line descrip-
tion of each field that must be specified by
the user. By studying the documentation,
the user may also become acquainted
with various philosophies for designing and
successfully implementing sub-slab de-
pressurization systems over low perme-
ability soils.
The RASSMIT program provides users
with a reasonable method to simulate any
number of subslab depressurization sys-
Printed on Recycled Paper
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tern designs. It may therefore be utilized
as a design tool, to provide for the predic-
tion and optimization of a sub-slab de-
pressurization system prior to actual
installation. By being able to run on per-
sonal computers using the DOS operating
system, the program can be applied to a
wide range of problems, from mitigation
system design by commercial mitigators,
to the development of building code rec-
ommendations by government agencies.
D. E. Hintenlang is with the University of Florida, Gainesville, FL 32611.
David C. Sanchez is the EPA Project Officer (see below).
The complete report, entitled "Reference Manual for RASSMIT Version 2.1: A Sub-
slab Depressurization System Design Performance Simulation Program, "(Order
No. PB93-155984; Cost: $17.50; subject to change) will be available only from
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection Agency
Center for Environmental Research Information
Cincinnati, OH 45268
Official Business
Penalty for Private Use
$300
BULK RATE
POSTAGE & FEES PAID
EPA
PERMIT No. G-35
EPA/600/SR-93/027
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