User Manual

Fire Safety

Building Technologies 049_Archives_and_Libraries_A6

V10271399_a_en.doc

Fire Safety & Security Products 03.2009

Pressure relief venting through another enclosure

Suppose there isn't an outside wall. Following topics should be taken into account:

– Is this an escape route (inc Fire Officer / Building Control)

– Cascade of pressure – escalating the problem

– False alarms elsewhere from entrained smoke

Suppose there isn't an outside

wall, venting into an adjacent

room (without pressure relief

vent) maybe acceptable if

venting through a warehouse

with a volume at least 70%

bigger.

Fig. 30 Pressure venting

Suppose there isn't an outside wall, venting into an adjacent room (without pres-

sure relief vent) maybe acceptable if venting through a warehouse with a volume

at least 70% bigger.

Suppose there isn’t an outside

wall, venting into an adjacent

room (with a pressure relief

vent) is possible, but cascade

pressure should be considered

(to open the flap and overall

pressure differential)

Fig. 31 Pressure venting

Chemical agents exert a small initial positive pressure,

– followed by a larger negative pressure,

– followed by a positive pressure of similar magnitude.

Fig. 32 Negative pressure “Gulp”

Negative pressure “gulp” The enclosure needs to withstand the negative pressure

phase, and dynamic of this.

Pressure relief venting in chemical agents can be engineered as pressure relief

flap pneumatically operated from the pressure within the discharge pipework, as

gravity flaps (preferred and most used option) or as electrically operated (rarely

used and not recommended).

Flo

Direction

Room A

Room must be 70%

Bigger than room A

Flow

Direction

Room A