ETL 1110-3-498
24 Feb 99
APPENDIX D
CLASS II, FILTRATION WITH LITTLE OR NO PRESSURIZATION
D-1. Facility Classification.
New facilities designated to have a Class II CP system do not require a CCA or an airlock for
personnel ingress or egress, however, a vestibule that acts as an airlock can be used to maintain
overpressure. This class of protection is applicable against a terrorist attack. Vulnerable outside
air intakes are protected by a continuous CBR filtration system sized for the normal facility air
intake requirements.
D-2. Guidance.
a. Existing Facilities. Existing facilities designated to have a Class II CP system will be
modified in accordance with this appendix.
b. New Facilities. New facilities designated to have a Class II CP overpressure system, or
to incorporate design features that ease future installation of a CP system, will incorporate the
requirements discussed in this appendix.
D-3. Design Requirements.
Major considerations for the design of Class II CP systems for both existing and new facilities are
listed below. Requirements for each item are discussed in subsequent paragraphs.
a. Toxic-Free Area Envelope.
b. Toxic-Free Area Overpressure.
c. Toxic-Free Area Envelope Air Leakage Rate.
d. Collective Protection System Design.
e. Collective Protection Operation and Maintenance Requirements.
D-4. Toxic-Free Area Envelope.
The total floor area required for the TFA is simply the area requiring collective protection. For
Class II facilities, required envelope sealing measures will be minimal. Noticeable leakage paths
should be sealed in existing facilities, and sealing measures should be incorporated in the design of
new facilities. Though an airlock is not required for this level of protection, a double entry door
such as a vestibule entrance can be used to maintain overpressure.
D-1
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