By Commander Brett Loughlin, Acting Director Preparedness Operations, CFS
The South Australian Grain Harvesting Code of Practice is a great example of industry and government working together to find practical solutions to an issue.
One of the required practices of the code is to suspend grain harvesting operations when the local actual Grassland Fire Danger Index (GFDI) reaches 35.
Fixed weather stations in the appropriate areas will generally give the most accurate readings of the GFDI. For those who do not have access to nearby weather station data, hand-held weather meters are also a reliable source of local weather conditions.
There may be a slight difference in temperature and wind speed between a hand-held weather meter and fixed weather station, however the results will be similar.
If using a hand-held weather meter, wind speed readings should be made in an open area at least 10 metres away from trees and other objects, facing into the wind with the meter held two metres high.
Temperature and humidity readings taken with a hand-held weather meter should be taken in the shade. These observations should then be averaged over a 10-minute period.
Using those observations, the GFDI should be measured using the following table which calculates the average wind speed for different temperature and relative humidity combinations that equate to a GFDI of 35.
For example, if the temperature is 35 degrees Celsius and the relative humidity is 14% (rounded down to 10%), then at this combination of temperature and relative humidity harvest operations should cease when the average wind speed is greater than 26 kilometres per hour.
One or two readings over an hour are unlikely to provide adequate data to enable a confident decision to be made.
Smartphone applications such as the NSW RFS Firefighter Pocketbook app can also help to calculate the GFDI.
Before the code existed, each local ag bureau or council area had different rules and policies. The code formed a basis for district harvesting codes of practice and brought about a consistent approach to fire risk management at harvest across South Australia.
Since its development over a decade ago, the code has made a tangible difference in reducing the number of fires and the amount of damage to crops, farm machinery and infrastructure and communities.
The GFDI provides a numerical assessment of likely fire behaviour which is then grouped into categories. These are:
- Low/moderate – GFDI of 0-11
- Small fires, easily controlled, likely cool weather with high relative humidity.
- High – GFDI of 12-24
- Fires may present some threat to property but first attack fire-fighting is likely to succeed.
- Very high – GFDI of 25-49
- First attack fire-fighting will likely fail, fires may move quickly and threaten property, indirect strategies may succeed. The Kangaroo Island bushfires in December 2007 occurred on a day of very high fire danger.
- Severe – GFDI of 50-99
- Fires are wind-driven, will spread rapidly and may be uncontrollable with spot fires likely to occur. Total Fire Bans are declared for categories severe and above.
- Extreme – GFDI of 100-149
- Aggressive fire behaviour usually driven by strong winds. Fire-fighting is ineffective. The extreme category presents a significant threat to life and property.
- Catastrophic – GFDI of 150 and over
- Fires on catastrophic days are uncontrollable until conditions ease. The Pinery fire in November 2015 and the Wangary fire in January 2005 occurred on days of catastrophic fire danger.
While it is not currently specified in the code as to when harvesting can resume, the CFS suggests waiting until conditions have obviously moderated and making the decision in conjunction with neighbours.
Details: For more information contact CFS Headquarters on 08 8463 4200.