Most observers believe these will never be used because they require Indonesia's co-operation. And Jakarta has given few indications that it comprehends the seriousness of the situation.

Smoke from dry-season burn-offs first became a regional problem in 1991, and has since evolved into almost an annual ritual. Bad outbreaks have occurred five times, usually fanned by periods of abnormally low rainfall.

The United Nations Environment Programme reported that the last big blaze, in 1997-98, destroyed about 10 million ha of natural forest and exposed more than 20 million people to dangerous air and water pollutants.