ETL 1110-3-498
24 Feb 99
C-3. Design Requirements.
Major considerations for the design of CP systems for both existing and new facilities are listed
below. Requirements for each item are discussed in subsequent paragraphs.
a. Button-Up Period and Floor Area Requirements.
b. Toxic-Free Area Envelope.
c. Airlock Requirements.
d. Toxic-Free Area Overpressure.
e. Toxic-Free Area Envelope Air Leakage Rate and Sealing Measures.
f. Collective Protection Overpressure System Design.
g. Collective Protection Control System and Operational Requirements.
h. Operation and Maintenance.
C-4. Button-Up Period and Floor Area Requirements.
The CP button-up period is determined by the command or authority having jurisdiction and can
range from several hours to several days. For off-site industrial accidents, the button-up period is
usually less than 24 hours. Button-up periods longer than 24 hours are generally restricted to
wartime. The button-up period influences the floor area requirements and the amount of
consumable and waste storage. Generally, the button-up period will not significantly affect the
performance of the CP system.
a. Less Than 24 Hours. A button-up period less than 24 hours does not require sleeping
areas. The occupant load will generally be a net 1.86 m2/person (20 ft2/person) depending upon
the classification of occupancy. The classification of occupancy, as stated in NFPA 101, may
require a higher or lower occupant loading depending upon the building classification. The
occupant loading will be coordinated with the authority having jurisdiction.
b. More Than 24 Hours. A button-up period greater than 24 hours requires sleeping areas.
The minimum floor area, with the use of single size beds, is approximately 5.6 m2/person (60
ft2/person). With the use of bunked beds, the minimum floor area is approximately 2.8 m2/person
(30 ft2/person).
C-5. Toxic-Free Area Envelope.
C-2
Previous Page
