The Vehicle

Vehicle cabins : Windows and doortrims

Burnover reports from the US and Australia suggest that the large glass areas of modern vehicles are a major threat to crews sheltering in truck cabins. There are repeated references to severe radiant heat loads transmitted through vehicle windows, with crews resorting to holding up clothing or fire shelters to windows for additional protection. The Australian studies (Cheney 1972) showed that 50% of the radiant heat incident on a closed car window was transmitted through to the interior.

In a least 2 cases, US crews were forced to abandon their vehicle cabins due to failure of the windows during a burnover. In addition, the Australian tests showed that ignition of the roof liners and door seals, which took around 4 minutes, even in their most intense "forest fire" burn, resulted in rising interior temperatures and dense smoke filling the cabin. Prior to ignition of the interior, the floor of the car remained a survivable environment. The US tests (Mangan 1997) showed that radiant heat loads on the outside of a vehicle door could cause its interior trim to ignite. This happened on 2 occasions after only 2 minutes in less intense fires. Following ignition, rapidly rising temperatures and toxic fumes again made the vehicle interiors uninhabitable. The earlier ignition of the door trims in these more modern vehicles may reflect the increasing use of plastics in modern vehicles.

The survivors of the Carey Gully tanker lost in 1983 and the State Forests Tanker burned over in 1997 both described dense acrid smoke filling their cabins during the burnover.

Conclusions
Vehicle cabins provide good protection from radiant heat, but the windows and door skins may limit the extent of the protection by excessively transmitting radiant heat. Ignition of the interior trim may prematurely limit the time the cabin remains survivable. Increasing use of flammable interiors may be increasing the importance of this problem.

Petrol Tanks

The enquiry (Mc Arthur 1966) into the loss of 8 men at the Wandillo fire in 1958 reported that 2 of the 3 trucks involved experienced petrol tank ‘explosions’, and that the tank which did not explode was protected by a bash plate that also shielded it from radiant heat. The Australian tests however found that actual explosions were extremely hard to induce in vented petrol tanks because the vapour inside was too dense to ignite. At worst, heating of the fuel in the tank caused it to vent vapour which burned at the vent, but after the fire passed, this went out leaving unburned fuel in the tanks. Actual ignition of the tanks took over 30 minutes, even in severe test fires, and genuine explosions could only be induced in sealed containers, and then only after prolonged heating by fire.

The fuel filler neck of Headquarters 81 reportedly burned off at Waterfall, and flames were observed around the filler cap of the Mylor Tanker as it was abandoned in 1980. It was subsequently recovered scorched but intact. The fuel tank of the Carey Gully Tanker still contained liquid petrol after the truck was burned out on Ash Wednesday II in 1983 (Figure 3).

Sealed portable fuel containers, such as those used to store chainsaw fuels, may pose a greater risk than vehicle fuel tanks, particularly if stored in an exposed position . Ignition of the chainsaw fuel cans during the Grays Point incident reportedly contributed to the deaths of 3 crew sheltering near the truck. A similar ‘Jerry Can’ also exploded on the State Forests Tanker burned over at Gwabegar (Figure 4). The US tests were conducted with empty fuel tanks for the safety of the investigators. The greater reliability of diesel engines under severe heat and smoke conditions, rather than the lesser volatility of the fuel during a burnover, has now resulted in their adoption as standard for most bushfire vehicles (Carter 1994).

Conclusions :
Despite popular concerns, petrol tank explosions have not been shown to be a real hazard in fires. It should be noted however, that modern vehicles now use sealed tanks, and truck fuel tanks are often elevated and unprotected by body work, both features may increase their vulnerability.

Flammability of other vehicle structures and equipment

Ignition of vehicle tyres, hosereels, fuel lines, air lines and other external equipment may contribute to the entrapment of the vehicle, or its subsequent destruction by fire.

During the Second Los Angeles burn, the mudflaps and hose reels on the urban appliance ignited, and the airlines to the brakes burned through, immobilising the vehicle. In another real world incident, a New South Wales Tanker was nearly lost when a small spotfire which ignited under the vehicle burned through the air line, locking the brakes and preventing it being driven clear. The crew of the Glen Park Tanker found the rear tyres of their appliance alight after the Creswick burnover, and were unable to access their knapsack sprays due to their storage position, externally, adjacent the burning tyres. Fire subsequently destroyed the truck.

Conclusions :
Fire appliances often appear to have been constructed with no particular attention to their external resistance to heat. Reasonable steps should be taken to minimise the flammability of external fittings, and to protect vital structures, particularly fuel lines, air lines and electrical wiring.

Mechanical Failures

Failure of truck engines to start, or continue to run, under severe heat and smoke conditions are common factors in burnover incidents. The petrol engine of the Mylor Tanker stalled after it was driven through flames at Longwood in 1980, forcing the crew to abandon it on the roadway, although without injury. It was seriously scorched as the fire passed over, but driven away the next day after cooling down.

On Ash Wednesday 2, the Tea Tree Gully Tanker was abandoned to the approaching fire after the rear differential failed, and the Cudlee Creek Tanker was abandoned after its petrol engine failed, apparently due to fuel vaporisation. Both vehicles were destroyed by fire and one crew member was injured.

In 1985, Santa Barbara County Engine 13 was engaged in protecting a house from an approaching urban interface fire. Conditions worsened, and the decision was made to retreat , but intense smoke and embers choked off its diesel motor and burned out the turbo. The crew were evacuated safely in another vehicle. Linda Engine 3 was destroyed at the 49er fire in 1988 when an electrical fault prevented the PTO pump from being disengaged. The crew escaped on foot.

The crews of multiple fire engines sheltered in their cabs during a prolonged (but not very intense) burnover in a safety zone in a forest at the Marre Fire in 1993, with Engine 2-7 suffering engine failure when its diesel engine ingested burning embers. In 1995, the petrol engined Kuna Engine 620 was already disabled on the fireground, probably with an engine overheat, when it was over run by an intense, wind driven brush fire and the 2 crew, sheltering in the cabin, were killed. Engine 97 was lost at the Fayette fire in 1996 when its engine stalled and would not restart as the driver tried to reverse out of flames when a backburn flared up with a wind change.

The diesel engined Los Angeles City Engine 10 stalled after being stopped in traffic in heavy smoke at the 1996 Calabassas Incident. The truck was then burned over whilst the crew of 4 sheltered under part opened personal fire shelters in the cabin. One (not wearing PPE) received serious burns, the others minor. The Glen Park Tanker was destroyed at the Creswick fire in 1997 when overrun by the parent fire whilst fighting a spot fire when its diesel engine stopped (apparently due to an incidental electrical fault, rather than ingestion of heat and smoke) and would not restart.

Conclusion :
The lesser reliability of petrol engined vehicles, and particularly of carburettor models, has been repeatedly demonstrated on the fireground and in the laboratory. Diesel engined vehicles however can still fail or experience severe loss of power if exposed to severe heat and smoke. In at least 2 instances, ingestion of embers rather than smoke disabled the engine. Suitable screens might reduce the risk of this.