hen I first went into research I wanted to study the impacts of forestry on catchment hydrology - we called it watershed management. I wasn't particularly interested in bushfires, but anyone studying forestry in the early 60s was well aware that fire control would be a major part of their job during summer. I worked for Alan McArthur, who was the first Australian scientist that set out to study how bushfires behaved in response to fuel and weather. We got on well together and I admired his work. In the end I suppose I was shanghaied into bushfire research.

Alan was hard-nosed, pragmatic and practical. He maintained that the only variable that could be controlled by man was the fuel on the ground. When I came to work with him he had just developed the first guidelines for undertaking controlled burning - we call it prescribed burning today - and expounded this philosophy during lectures at the Australian Forestry School. Perhaps a whole generation of foresters who had trained under McArthur came out believing implicitly in his philosophy.

McArthur also maintained that in planning for fire control you had to plan for the 'worst possible' conditions, and he used the 1939 fires as his benchmark. He developed the Australian Fire Danger Rating System with an index between one and 100, where 100 represented the 'worst possible' weather conditions. Pedants would say these were the worst recorded conditions at that time - but 'worst recorded' didn't have the same impact as 'worst possible' for a man selling a new system. It is still in use today.

I came into forestry knowing nothing about it. I was raised at Newhaven, a fishing village on Phillip Island, where severe bushfires were rare. Although I remember burning off the dead grass around our home as soon as it became dry enough to burn at the start of every summer. Everyone did that back then. I remember summer nights in the 50s we would clearly see the flames from bushfires burning the forests on the foothills of the Strezleckie Ranges across Westernport Bay. My uncle had a farm near Boolarra and was burned out by bushfires during the 50s, but we never really talked about it.

When I started working, Australian forestry was coming out of an era of complete protection. It was only just being recognised that the ash forests regenerated after severe bushfires, and if we were to successfully regenerate the ash forests after logging, the areas had to be burnt and seeded into the ash beds.

As a student, I worked in the alpine ash in northern Victoria with Ron Grose, who was researching the conditions required to successfully regenerate the forest. Around Mount Buller, these forests had not been severely damaged in the '39 fires, but evidence of the regeneration from the fires in mountain ash forests east of Melbourne some 20 years earlier was clearly visible.

For me there was no question about McArthur's philosophy. The fires that regenerated these forests had been extensive and particularly severe. There was no reason why they should not occur again, and these were the conditions that we should plan for.

In a normal summer, the ash forests are too wet to burn. The fuel builds up for over 100 years or more, and at first glance these forests don't appear as hazardous as the fuels of the dry forest surrounding the ash. It is only when you realise that the old forests may have more than half of metre of accumulated organic matter on the forest floor, that you realise the energy available if conditions ever become dry enough for all this material to burn.

My first realisation of what a fire danger index of 100 - the weather conditions during the 1939 fires - really meant, was when I investigated the Hobart fires in the mountain ash forests of southern Tasmania in 1967. Many people, including professional foresters, did not believe that southern Tasmania could ever experience the extremes of weather that had occurred on the mainland.

It was only the students of McArthur, convinced by his rhetoric, who believed that these conditions could, and would, occur again - even in Tasmania. When they did occur, the outcome was much the same in as in Victoria in 1939. The fires burned whole communities, and in less than eight hours, 62 people lost their lives. The ferocity of the fire-generated winds uprooted huge trees and snapped others half way up.

It was practically a mirror of the historic photos we had seen of the 1939 fire damage. The deep layer of organic soil that had accumulated for 200 years on the forest floor burned completely down to mineral soil and killed the trees even when the conditions were mild.

In absolute terms, the combination of drought, temperature, relative humidity and wind speed that makes up the fire danger index of 100 has been exceeded on Ash Wednesday in 1983. Although I suspect that the wind speed recorded at Melbourne in 1939 - that McArthur used as a measure for the index - was lower than the wind speed that would have occurred in the mountainous regional areas of Victoria.

Nevertheless, the weather conditions of January 1939 still remain as a benchmark for the worst possible weather conditions. There were three days of extreme fire danger that occurred within a week. We have not seen such a prolonged period of extreme weather in 100 years of weather observation. We do not know the frequency at which these conditions will recur. What I do believe is that these conditions will happen again, and when they do, any bushfires that happen to start will be just as extensive and just as severe as 1939.