What does it mean when they say a fire is x% contained? x% of what? is it a measure of perimeter or area? Also how do they define containment?
I asked exactly this question at the town hall briefings for a big fire near us a couple of years ago. The percentage refers to perimeter.
When the fire is surrounded. Doesn’t speak to it being under control. Under full containment can go to hardly any containment with celerity.
To clarify the clarification, it means the fire is surrounded by breaks: bare earth, creeks, back-burns etc. Those are all locations where the fire should be easily stopped by a competent fire crew. But as IAmNotSpartacus notes, they aren’t infallible. Fire can jump most breaks, and with a sudden change in wind speed or direction or a spot fire drawing the crew away from the break location, the fire can move across the break in minutes and become totally uncontained.
Containment is a useful term when evaluating where to place additional resources, but it shouldn’t be taken as a measure of danger.
So a day or two ago I read that the fire near Los Alamos was 3% contained. Based on the above comment that would mean that they had this small fire break that extended to 3% of the fire’s perimeter. But for such a small length it would seem that it would be easy to go around it, so wouldn’t it be 0% contained? So 50% or 80% containment makes sense, but just a few percent seems confusing to me.
If a firebreak is overtaken and the outer perimeter of the fire is again entirely unchecked, then they will indeed say it’s “0% contained.”
It has happened a few times where firefighters working along a small break actually had the fire spread out from both ends and meet up behind them.
You really have to look at the number in context (unless it’s very large or very small). Especially in rough terrain, fires won’t burn in a nice, neat circle.
When you see a small number like that, it usually indicates that a break has been constructed around a high value area specifically to stop this fire.
For example, if a fire is burning on a 5 km front in sagebrush in rough country, nobody cares much about controlling it. It will burn itself out in good time and won’t do any great ecological or economic harm, so nobody wants to risk lives and equipment trying to fight it. But if there is an electricity substation downwind of the fire, that becomes a problem. So the fire crew goes in, backburns the few hundred metres around the perimeter of the substation, and leaves. The few hundred metres that have been burned are duly recorded on the containment map, as a 3% containment.
And you’re right. The fire could easily burn around the containment, but nobody cares. The only area of concern in the sunbstation itself, and it’s protected. So if the fire burns all around it nobody gives a toss.
So why report it at all? Because it’s procedure. Fire control is a major logistical task. Experience has taught us how to co-ordinate the job, and one of the things we do is make sure that the control centre has a good picture of the overall situation. So all the individual players report their own efforts, and that gets mapped and collated by the control centre. The idea being that the 3% break around the substation may be worthless by itself, but there might be dozens of other areas that have also been treated the same way. In the event that it becomes necessary to stop the fire, it might be possible to join up all those little areas to form one big break. If nothing else they provide refuges for crews that are being surrounded.
So the little areas all get reported back to the control centre. And then the press release includes those figures as part of a standard report. The press then reports them without actually considering whether they are meaningful.
Or, in short, the 3% figure was meaningful for the purpose for which it was originally reported, but by the time it makes it to your local radio station, it has become truly meaningless. As you say, the distinction between 3% and 0% is non-existent.