ETL 1110-3-498
24 Feb 99
b. New Facilities. For new facilities, the TFA envelope air leakage rate will be calculated
using the effective leakage area procedures in the ASHRAE Handbook of Fundamentals. The
leakage calculations will be performed for the TFA envelope including the walls, roofs, floors,
doors, windows, sole plates, mechanical and electrical penetrations, ceiling-wall joints, isolation
dampers, etc. The overpressure of the TFA will be used as the differential pressure in determining
the TFA envelope leakage rate. Appendix G will be used as a guide to confirm the TFA envelope
unit leakage rate as determined by the calculations. Care should be taken during design and
construction to ensure that proper sealing of penetrations is performed and that continuous air
leakage control barriers are used in the TFA envelope. A blower door test of the TFA envelope
should be performed after construction to verify the leakage rate and ensure that the CP
overpressure filtration system has sufficient capacity.
D-7. Collective Protection System Design.
a. Airflow Filtration Capacity. The airflow capacity of the CP overpressure filtration
system is the sum of the following two components: TFA envelope air leakage rate at the design
pressure differential and the ventilation air intake rate that meets the facility exhaust requirements.
The CP filtration system blower total static pressure will be designed to include the filtration
system with dirty filters, ductwork system pressure losses, and the overpressure requirement of the
TFA. The HVAC system must be designed, operated, and maintained to provide uncontaminated
air to the TFA. It will be located in a contamination-free mechanical room to insure that negative
pressures induced in the ductwork by HVAC equipment located in the mechanical room will not
draw in contaminated air to the protected area. Filtration systems will conform to Appendix E.
b. HVAC Design Requirements.
(1) Existing Facilities. For existing facilities, an analysis will be performed to determine if
the existing HVAC equipment can be utilized for CP operations to maintain a slight overpressure.
If necessary, mechanical equipment modifications will be made to existing facilities and increased
equipment capacities provided for new facilities. The HVAC system must be designed, located,
operated, and maintained to provide uncontaminated air to the TFA. The outside air intakes will
be secured to inhibit the direct insertion of contaminants.
(2) New Facilities. For new facilities, the HVAC equipment will be designed to incorporate
the requirements to maintain a slight overpressure and maintain indoor design conditions. The
HVAC system must be designed, located, operated, and maintained to provide uncontaminated air
to the TFA. The outside air intakes will be located in an inaccessible location or secured to inhibit
the direct insertion of contaminants.
(3) Indoor and Outdoor Design Temperatures. Indoor dry and wet bulb design
temperatures and outdoor design temperatures will be determined in accordance with TM 5-810-1,
associated references, and mission requirements.
D-3
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