ETL 1110-3-490
13 May 98
b. More Than 24 Hours. A button-up period greater than 24 hours requires rest and relief
areas. The minimum floor area, with the use of single size beds, is approximately 60 ft2/person.
With the use of bunked beds, the minimum floor area is approximately 30 ft2/person.
B-5. TFA Envelope.
The total required TFA floor area is determined from the button-up period, the number of people
sheltered, and the required floor area per person. Generally, large open areas; e.g., common areas,
multipurpose areas, gymnasiums, etc., provide the most efficient floor area for protecting a large
number of personnel. The TFA envelope should include bathroom facilities and, if possible,
kitchen facilities.
B-6. Airlock Requirements.
Personnel that ingress and egress the TFA during CP operations must process through an airlock.
The airlock maintains TFA overpressure, prevents the migration of airborne contaminants into the
TFA, and purges personnel entering the TFA. The number of airlocks required depends on the
number of personnel that ingress and egress during a given time period.
a. Stand-Alone Airlock. For existing facilities, the stand-alone two-stage airlock discussed in
Appendix C will be used. This airlock is designed to process two people into the facility within 8
minutes with 4 minutes in the first stage and an additional 4 minutes in the second stage. An
integral 340 m3/hr (200 cfm) air filtration unit is used to provide the necessary air purge rate upon
which the dwell time is based.
b. Integral Airlock. For new facilities, an integral single-stage airlock will be incorporated into
a vestibule area. The airflow purge rate through the single-stage airlock will be based on equation
B-1.
6.9 V
Q'
(eq. B-1)
T
where:
Q = airflow, cubic meters per minute
V = airlock volume, cubic meters
T = purge time, minutes
Airlock airflow is driven by internal overpressure from the TFA. Uncontaminated air from the
TFA will enter the airlock near the ceiling and exhaust near the floor. The airflow rate through the
TFA will be monitored by an airflow measuring station or measuring device that can be field
calibrated, and the airflow rate will be displayed at a CP control panel. The airflow rate through
the airlock will be controlled by a one-way flow control gravity damper. A warning light will
B-3
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