Bushfire Report

        A steel fence after testing at the Mogo site.

    RESEARCH OUTCOMES                                          TOXIC CONTAMINANT RELEASE                       dispersion, and the degree to which site
    SMALL-SCALE EXPERIMENTS                                    The major issue related to the combustion       occupants are exposed to the gases.
    This investigation confirmed that Colorbond                of Copper Chrome Arsenic (CCA)-treated
                                                                                                               LARGE-SCALE EXPERIMENTS
    steel fencing panels do not ignite and                     pine is the release of significant levels of
                                                               arsenic, as well as the high arsenic content    Colorbond steel
    contribute significant heat release during
                                                               in the timber ash (2.2% by weight). Arsenic     This had the best performance as it is a
    cone calorimeter exposure. Both pine and
                                                               can cause eye, throat and respiratory           non-combustible material. It maintained
    hardwood materials provide significant heat                                                                structural integrity as a heat barrier under
                                                               irritation, and is a confirmed human
    release under these exposures. The ranking of                                                              all experimental exposure conditions, and it
                                                               carcinogen. It is worth noting that the
    performance of these materials in descending                                                               did not spread flame laterally or contribute
                                                               National Environmental Protection Measure
    order are: Colorbond steel (insignificant                                                                  to fire intensity during exposure. The fencing
                                                               provides health impact criteria for arsenic
    release), new hardwood, old hardwood, old                                                                  reduced radiation levels within the fencing
                                                               in soils in the range of 0.01-0.05%, and so
    pine and new pine.                                                                                         boundary to below 5 kW/m2 immediately
                                                               the dispersion of CCA-treated pine ash
    Of particular interest was the effect moisture             could lead to site contamination, especially    behind the fencing system during all radiation
    content had on the time to ignition for all                where large quantities of the material has      exposures, and reduced the radiant heat
    these materials. In particular, the observation            been burnt. Analysis also showed that it        exposure on a structure nine metres from the
    that a material exposed for six hours to 40                could be harmful for a person to come into      fencing by at least a factor of two for the given
    degreesC and 20% relative humidity had                     direct skin contact with the ash.               fire size in the experiment.
    similar fire properties to the same material               As for Colorbond steel, two human               Hardwood
    when conditioned at same temperature and                   carcinogens (benzene and formaldehyde)          Although combustible, closed paling
    relative humidity until moisture equilibrium               were detected in the air toxicity experiments   hardwood fencing maintained a radiant heat
    was achieved. This highlights a significant                conducted on this material. While these         barrier during radiation-only exposures,
    point – that the fire behaviour of these                   gases were detected, the risks they present     resulting in a reduction in heat received at the
    specimens was influenced more by the surface               would depend on the levels of exposure to       structure. In exposures where flame contact
    moisture content rather than the average                   nearby occupants, which is unknown. In          of the fencing occurred, flame emission
    moisture content of the specimens, and hence               fact, evaluating the risks from these gases     from the fencing provided additional radiant
    the weather conditions on the day of fire                  will depend on combustion conditions,           heat exposure on the structure. Open paling
    impact will have a significant effect on the fire          the quantity of material burnt, the volume      hardwood fencing systems were partially
    performance of timber elements.                            of combustion gases generated and its           effective in attenuating incident radiation

3    Background briefings on emerging issues for fire managers from AFAC and Bushfire CRC.                                                                         3