For a smoke Zone and during the operation of exhaust fans, negative pressure in the smoke zone draws air with rich oxygen from adjacent zones which has an adverse effect causes more fire growth, so smoke management hand book limits exhaust air withdrawal rate to 6 air changes per hour as a maximum value.
According to SBC 201, All smoke and heat removal systems are not required if Early suppression fast response (ESFR SPR) are used. or with a response time index of 50 (m.s)^1/2
According to the smoke management handbook, air or smoke scavenging system should be supported by fresh air make-up system because smoke extraction fans may create excessive negative pressure inside the building, which by turn may cause windows glass failure.
Saudi building codes (201 & 801) limits the smoke removal rate to only (2 ACH) (Air Changes Per Hour) of volume of smoke zone with a maximum capacity not to exceed 14.2 m3/sec. For make-up air, the minimum gross area of make up air inlets shall be 0.74 m2 per 0.47 m3/s of smoke exhaust.
