ETL 1110-3-490
13 May 98
APPENDIX C
TWO-STAGE AIRLOCK DESIGN
AND PROCESSING PROCEDURES
C-1. Airlock Description.
As shown in Figure C-1, the two-stage airlock has outer first stage and inner second stage
compartments. The outer compartment is used to remove protective garments while it is being
continuously purged by the flow of filtered air. After protective garments are removed, personnel
enter the inner compartment which is then purged of vapors during the dwell cycle. After the
dwell period, personnel enter the toxic-free area (TFA). Clean airflow for these cycles is provided
by a dedicated filter blower unit connected to the inner compartment at the filtered air inlet.
C-2. Airlock Features.
The following features are common to an integral or stand-alone airlock.
a. Timers. A mechanical bell timer to time the dwell and purge cycles is required in each
compartment.
b. Windows. A window is required at each compartment to determine if it is occupied.
c. Lights. Lights are required because the interior lacks adequate natural lighting.
d. Purge Vents. The two-stage airlock has fixed rather than adjustable purge vents because it
has a dedicated filter blower unit that makes the airflow rate easy to maintain. For an airlock
without a dedicated filter blower unit, a variable area purge vent or flow control valve is required
to adjust the airflow rate and maintain the required purge rate.
e. Monitoring Port. The monitoring port allows the chemical agent monitor (CAM) detector
inlet to be inserted into the outer compartment by a CAM operator located in the inner compart-
ment. This allows the CAM operator to determine if there is agent vapor in the outer compart-
ment. With a negative reading in both the G and H mode (about 10 seconds each), the operator
may determine that a shorter or longer dwell period is required. A second CAM check for sorbed
vapor can then be performed in the inner or second stage compartment.
f. Caulking. Caulking should be applied to all joints to limit uncontrolled air leakage.
g. Paint. Painting the interior and exterior surfaces with epoxy paint is required to minimize
the sorption of liquid and vapor agents.
C-1
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