by David Nichols, CFA Manager of Research and Development
Bushfire firefighting, tanker vehicle entrapment, and fire burnover are life-threatening situations for fire fighters. The most dangerous Australian tanker/engine burnovers typically occur on a narrow track in a eucalyptus forest environment. The abundance of elevated and surface fuels between an entrapped tanker and the fire front can allow for a sudden escalation of fire intensity associated with changes in slope or following a wind change of direction and/or strength.
Burnovers are characterized by an initial period of strong radiant heat followed by peak flame contact from a fast moving flame front. This initial period is followed by a short intense short flame immersion of the tanker of less than two minutes. After the flame front passes the tanker crew may still be impacted by significant radiant heat from the fire as the flame front progresses away from the tanker. The fast moving fire flame front might only allow for an extremely short period of time for the tanker crew to become aware of the threat and to prepare for a burnover. Due to the fast moving nature of a bushfire in a burnover situation, any crew protection system needs to be easily and rapidly deployed by the crew.
Country Fire Authority (CFA) Victoria fire fighting tanker crew protection systems have been evolving since the 1977 Western District fires when standard tanker design and heat shielding were first deployed. After the 1983 Ash Wednesday fires where 12 CFA volunteers were lost in a burnover, the tanker fleet was upgraded with all diesel powered vehicles and pumps and research was completed into fire resistant materials on tankers. Significant crew protection component research commenced following the 1998 Linton fire where five CFA volunteers perished when their tanker was entrapped and burnt over.
The objective of the crew protection system research since 1998 has been to provide an evidence based system that will protect tanker based fire fighters in a burnover entrapment situation during a bushfire of high intensity of up to 10,000 kW per metre. The bushfire conditions that occurred during the Linton bushfire have been used as the benchmark for the research.
Since the Linton bushfire, the CFA has undertaken research and development into a variety of tanker crew protection methods. The research has resulted in the installation of crew protection systems commencing in 2006 on new build medium tankers (2000 litre water carrying capacity) and heavy tankers (3000 litre water carrying capacity) in the CFA fleet. A retro-fit crew protection system for all CFA medium and heavy tankers was completed on 1200 tankers prior to the 2013-2014 fire season. Post-Linton crew protection systems installed on new tankers include personal protective radiant heat shield blankets, low-level water indicators, water spray deluge systems, internal cabin drop down radiant heat shielding, additional radiant heat shielding around water pump systems and vulnerable tanker components, a reduction of plastic materials on the external surfaces of the tankers, metal air cleaner filters, and flame resistant hoses and cabling. Crew training, with a requirement of minimum fire fighter skills and situational awareness, has also been emphasised since 2000.
Even with new crew protection and improved situational awareness training, multiple CFA tanker entrapment and burnovers have occurred. Fortunately there has been no serious injury or loss of life since the initial tanker crew protection system installations in 2006.
In addition to the validation of the medium and large tanker development, CFA is conducting research into crew protection systems for the ultra-light tanker vehicles. Given that the ultra-light vehicles do not carry large quantities of water, the research has been directed at water enhancing products including Class A foam and polymer gels. The water enhancing products have been tested on ultra-light vehicles at the Bushfire Flame Front Simulator, managed by New South Wales Rural Fire Service and CSIRO, located at Mogo, New South Wales (Figure 1). The delivery system of the polymer gel product underwent validation testing at a grassfire burnover scenario test at Wangaratta, Victoria (Figure 2) prior to the Brucknell forest fuel validation test (Figures 3-4).
Since the medium and heavy tankers in the CFA fleet have a large water carrying capacity, a water spray system that uses 500 litres of water over five minutes is a good protective agent for those tankers. CFA also has a large fleet, over 150 units, of ultra-light tankers with a much smaller water carrying capacity (less than 500 litres) that limits the use of water as a part of a crew protection system. Since 2014, CFA has been researching the use of water enhanced technology, including polymer gels and A Class Foam products as a part of crew protection for the ultra-light tankers.
The CFA Research and Innovation Unit, in collaboration with the Commonwealth Scientific and Industrial Research Organisation (CSIRO), recently completed an experimental bushfire burn test to determine the survivability of crews in three differently protected fire fighting tankers in an entrapment burnover situation.
CFA identified a suitable site for conducting a high intensity experimental fire in a forest environment to validate the crew protection system research and development process. Objectives of the experimental fire were (1) to conduct a high intensity experimental burn over scenario, with a wide fire front (approximately 100m) and target fire line intensity of at least 10,000kW/m (a benchmark from the Linton bushfire burnover), and (2) to field test the following CFA crew protection systems:
- A retrofit water spray deluge system installed on a medium tanker (2000 litre water capacity).
- A polymer gel delivery system fitted to an ultra-light tanker (400 litre water capacity).
- A Compressed Air Foam System (CAFS) installed on an ultra-light tanker (400 litre water capacity).
The field validation burnover tests were conducted at an area (Brucknell Scout Camp near Timboon, Victoria) with bushfire forest fuels, topographic influence, and weather conditions similar to conditions that have occurred in past Australian tanker entrapments and mpst fatal burnovers.
CFA crew protection systems have been researched and developed through a rigorous scientific process of structured, repeatable experiments on the CSIRO bushfire flame front simulator (Figure 1), followed by a field validation experimental test fire burns in grassland fuels (Figure 2).
The final system validation experiment was conducted in the forest bushfire fuels at the Brucknell test site (Figures 3-4). The forest fuel validation test is based on a fire of 10,000kW per metre that would build its intensity over a period of time determined by the fire level of intensity, with a total flame immersion of the vehicle of less than two minutes. The burnover would require five minutes of water coverage on the tankers to protect the crew from the most intense radiant heat levels and the flame immersion phase of the fire burnover.
The delivery system for the Class A foam product was tested at the Brucknell forest fuel validation test. This experimental validation tested a medium tanker with current crew protection system, a polymer gel protected ultra-light tanker and a Class A foam protected ultra-light tanker (Figures 3-4).
The average fire intensity of the experimental fire was 19,000kW per metre, with a peak intensity impact on the tankers of 31,000kW per metre.
In addition to testing the radiant heat and flame contact on the tankers, internal cabin air toxicity was also measured. Air toxicity exposure criteria within the tanker cabin during the fire burnover experiments are based on two considerations:
- Tenability – the fire crew will be able to occupy the cabin for the bushfire burnover period without experiencing intolerable irritation, significant loss of alertness, or irreversible health effects.
- Survival – the fire crew will be able to occupy the cabin for the bushfire burnover period without loss of consciousness or loss of life.
All the tanker crew protection systems provided adequate crew air toxicity tenability and survivability objectives during the experimental burn test.
The crew protection system over-spray of one to two metres moistened the fuels around the tankers and thus decreased fuel combustion and the radiant heat load and direct flame front contact on the tankers.
The temperatures on the outside of the tankers ranged from over 300?C on the medium tanker to over 400?C on the gel protected ultra-light tanker. The inside cabin temperatures at medium seat height level were:
- Medium tanker: <50?C for seven minutes after the fire flame front passage
- Gel protected ultra-light tanker: <50?C for four minutes after the fire flame front passage
- Class A foam protected ultra-light tanker: <50?C for 5 minutes after the flame front passage.
Prior CFA research has shown that fire fighters, in normal wildfire protective clothing, can be exposed to 55?C temperatures for 20 to 25 minutes before any increase in body core temperature. The test of the temperatures inside the cabin demonstrate that, while fire fighters may be hot and uncomfortable during the flame front impact and burnover, they would certainly survive the burnover in the protected vehicles.
The bushfire flame front entrapment and burnover experimental test that impacted the medium tanker validates the crew protection system research and development of systems now installed on over 1200 medium and heavy CFA tankers.
The results are very encouraging from CFA testing of crew protection systems incorporating water enhancing products for ultra-light tankers. CFA will continue the research and development of water enhancing systems until it can confidently incorporate a validated system into the fleet.
Evidence based tanker crew protection system improvements and bushfire situational awareness training continue to help make tanker-based fire fighting crews safer on the fireground in the unexpected occurrence of a bushfire entrapment and burnover.