Improving the Protection Provided by Bushfire Appliances

What are the current protective systems?

Current appliance protective systems include high sides, crew havens, fixed sprinklers, hand held hoselines and radiant heat curtains. The present generation 2000 and 3000 litre bushfire appliances used by the South Australian Country Fire Service (CFS) are built on standard commercial 4WD truck chassis’. The crew of 6 is split equally between the drivers cabin and a ‘crew haven’ on the tray immediately to its rear (Figure 7).

In the event of a burnover it is intended that 3 will shelter in the cabin and 3 in the crew haven. The drivers cabin is a standard commercial truck cabin and has no additional heat protection. Low volume sprays are mounted on the truck bumper to cool the front tyres but are not intended for cabin protection. A woolen blanket is carried in the cabin for crew protection. The rear crew haven is a purpose built structure intended to provide both radiant heat and rollover protection for the 3 crew on the rear. It has a heavy steel frame, bench seating for 3 with lap belts and a roll down reflective heat shield. It is clad in fibreglass and has equipment lockers outside, giving double layer protection for the sides. Two short 25mm self defense hoselines, plumbed to the main water supply of the truck and used for fire suppression on the move, are available at this position. In the event of a burnover it is intended that the 3 rear crew will shelter inside the crew haven with the reflective screen down and operate the 2 self defense hoselines for additional protection. A similar system, minus the roll down screen, was used on the Geelong City Tanker which survived the Linton Fire.

The vulnerabilities of present tankers

The US tests , and the analysis of the burnover reports, suggested that whilst the cabin of the truck can provide good protection for the crew during the burnover, the windows and doors are vulnerable to the effects of radiant heat. There are numerous reports of personal fire shelters being held up to windows to block the influx of radiant heat. The provision of a drop down or pull around radiant heat screen inside the vehicle cabin would be an inexpensive and worthwhile improvement. The South Australian Country Fire Service is presently considering such a screen (Figure 8). The door skins themselves appear to be unexpectedly vulnerable. The effects of radiant heat on the outside of the door produced early ignition of the door liner in 2 of the US tests. In each case, this resulted in the cabin rapidly filling with heat and choking smoke which would have forced the premature evacuation of the cabin during the burnover. This phenomenon may become increasingly important with the increasing use of plastics in modern vehicles.

Improving the radiant heat protection for the vehicle doors, possibly by applying a reflective coating, or a clip on screen, akin to a ‘tropical roof’, is a major priority. The crew haven presently fitted on the working tray of South Australian Country Fire Service appliances probably provides excellent radiant heat protection, indeed, given its lack of windows and door trims, it may provide significantly better protection than the driver’s cabin.

There is a trend in Australia towards the adoption of dual cab designs for Bushfire appliances, with the elimination of the crew haven. This may be a retrograde step in terms of radiant heat protection, particularly if the vulnerabilities of the windows and door trims are not addressed. It should also be noted that many burnovers occur with little warning, and adequate crew protection must be provided for both the cabin and the working area on the back of the appliance.

The use of handlines or dedicated self defense sprinkler systems to project a curtain of water as a radiant heat shield between the vehicle and the fire clearly has significant potential to improve survivability in the more severe burnover incidents. Hand directed hoselines may be more effectively directed towards the approaching fire, but fixed sprays allow the crew to take cover. In limited trials here, the presently recommended strategy of retreating to the safety of the crew haven and blindly directing a hand held hose from within, proved ineffective, as the spray tended to favour the rear of the truck and provide limited protection for the crew haven and none for the drivers cabin. Both systems are reliant on a supply of water and the continued operation of the pump. Tanker designs presently in use in South Australia provide inadequate protection for the pump. A variety of fixed sprinkler systems are undergoing wind tunnel evaluation in New South Wales at present.

Analysis of the US tests, and the cases above, would suggest that such systems should :

• be capable of operating for at least 2 minutes on the dedicated water reserve
• be easily operated from both the drivers cabin and the working area on the tray
• be capable of operating effectively in high winds
• operate effectively at all ranges of pump delivery from idle to full power.

In limited trials with a variety of rotary head and venturi sprinklers we noted :

• it is difficult to provided adequate cover with a single, vertically directed nozzle as such a set up is excessively affected by winds
• the use of multiple smaller spray heads inclined more to the horizontal than the vertical markedly improved the cover provided by the spray.
• rotary head sprinklers were more affected by variations in supply pressure, producing an excessively fine spray at high supply pressures. In addition they may be more prone to failure due to failure or jamming of the moving parts.

As long ago as 1958, the coroner noted the vulnerability of the petrol tanks of bushfire appliances to fire. The lesser volatility and greater reliability of diesel fuel has lead to its increasing adoption as the fuel of choice, and there are no identifiable reports of diesel tank ignition in survivable burnovers. A degree of heat shielding for these tanks may however be prudent.