Essentials
By Selele Mashilo
SELELE MASHILO
Selele Mashilo has a mechanical engineering diploma from Tshwane University of Technology and a refrigeration and air-conditioning diploma from Unisa . His experience includes over a decade in government as deputy-director building services before rejoining the private sector in 1998 as HVAC & R project engineer . He is the former chairperson of the Refrigeration and Air Conditioning Empowerment Forum of SA ( RAEFSA ), the Air Conditioning and Refrigeration Industrial Council of SA ( ACRICSA ), and Black Energy Services Companies ( BESCO ).
HVAC , FIRE AND SMOKE CONTROL
CONTINUED
In the previous issue of RACA Journal , I discussed fire smoke in a building by considering service shafts and lift shafts being designed around the possibility of fire smoke stack effects . In this issue we look at barriers in the building structure .
Smoke control uses barriers in the building structure . The barriers are the building walls , floors and doors . The other barriers may be in the form of mechanical fans for building ventilation . The two basic principles of smoke control are the following , which will be looked in detail :
• Airflow can control smoke movement with sufficient air velocity
• Air pressure difference across barriers used to pressurise the shafts during fires . The doors act as smoke barriers and , as can be seen from the above diagram , smoke will never enter the lift shafts so that lifts may be used by the smoke control technicians in all building levels to extinguish fires .
AIR FLOW APPLICATION PRINCIPLES In building corridors , air flow velocity is used to prevent smoke from travelling in certain directions . The diagram below shows this concept in operation .
AIR PRESSURE APPLICATION PRINCIPLE
ASHRAE Handbook , 1987
In multi-storey buildings lifts are used , and lift shafts may transfer smoke from the affected areas to other unaffected areas during a fire . Lifts may also be used as fire escape routes for fire technicians .
These shafts transport smoke during fires using buoyancy and expansion . To use lift shafts for smoke control , ventilation fans are
ASHRAE Handbook , 1987
This principle makes evacuation of tenants much easier when the direction of smoke flow is known . Corridors of large buildings may be favourable for smoke acceleration , but if ventilation fans are designed and positioned properly , they can be safe passages for evacuating tenants from large buildings . RACA
References : 1 . ASHRAE
www . hvacronline . co . za RACA Journal I January 2021 61