on plastic roof material usually installed to enhance natural light in commercial buildings has melted and allowed smoke and heat to disperse rather than spread. The advantages gained in terms of improved visibility, the ability to observe obstacles, quick identification of the fire seat, and reduced heat conditions all enhance knock down and control of the fire.
Natural ventilation both lateral and vertical by utilising building openings such as skylights, ventilation shafts, stairway doors, windows and removal of a section of roof are the most common and fundamental methods.
The decision to open a roof to assist ventilation is an operation that requires careful consideration and experience. Coordination is essential with the crews working inside the structure, observation of the wind direction is important to establish a downwind location especially on sloping roofs, utilise existing roof openings and note any roof loading such as header tanks and other building services equipment.
Avoid structural supports, work with the wind to your back or side, and cut one large hole rather than several smaller ones. Utilise rooflines and safety harnesses on all occasions.
Mechanical and negative pressure ventilation methods
A number of mechanical and negative pressure ventilation methods can be deployed such as utilising the natural venturi principle created by locating hose streams in door or window openings discharging to the exterior. This method has been used by firefighters for generations and is highly effective given the right conditions.
Other mechanical methods using Hi-X foam generators or extractor fans including some air conditioning systems can also be utilised to create negative pressures inside a structure thereby increasing air flows which assists in the removal of smoke and hot gases.
The correct utilisation of positive pressure ventilation introduces cool air and can increase localised flaming. But the advantages in removing the hot gases and replacing them with cool air reduces the temperature and ability of the fire to develop. The clear entry path created by the fan improves visibility, reduces temperature dramatically and allows firefighters to locate and extinguish the fire more quickly.
Whichever method is employed, the importance of implementing some form of tactical ventilation at an early stage in fire operations positively assists in rapid control, quicker knock down, safer operations and a more sophisticated and professional approach to limitation of damage and fire extinguishment.
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