Former world champion Jenson Button said Thursday that severe haze would pose a "big health risk" to drivers in the Singapore Grand Prix as organisers remained on edge despite an improvement in air quality.

The 2009 world champion, a dedicated triathlete, told AFP he had to skip outdoor workouts due to the acrid smoke being blown over the city-state from forest and farm fires in neighbouring Indonesia.

The haze problem has become a chronic threat to the world's first night-time Formula One race as well as a festering bilateral issue with Indonesia, where fires have traditionally been used to clear land for cultivation.

"It would have been a big health risk if it was as bad as yesterday," the British driver said in an interview, referring to the officially declared "unhealthy" levels of air pollution when he arrived from Phuket, Thailand.

Button, 35, said he practised with professional triathletes over a five-day period in the Thai resort island in preparation for Singapore.

The Singapore race is held under floodlights on a narrow and bumpy street circuit which snakes past historic and modern landmarks of the wealthy former British colony. The nearest Indonesian islands are less than an hour away by ferry.

"The biggest issue would be coughing in the race but I think it's (worse) post race because you are pushing your body very hard in the race, you're going to have health issues after the race," Button said.

Singapore's air quality was considerably better on Thursday after torrential downpours the past two days, but race officials have warned that conditions could change quickly.

"I think it'll be fine this weekend, fingers crossed," said Button, who was speaking under a gray sky on a boardwalk overlooking the posh Marina Bay race circuit.

"We all know that it's not good breathing in fumes. You're racing a car and your heartbeat's very high."

He said for some drivers the heart rate during a race can reach as high as 170 beats per minute.

"For me I am lower, I am more relaxed in the car... about 150, 155 which is quite high for me because I do a lot of training."

Organisers said on Tuesday that the haze situation was volatile but there were no plans to change the schedules of the race and related events, including a post-race outdoor concert by rock icon Bon Jovi.

"The haze situation is highly changeable not only from day to day, but from hour to hour," Singapore GP said in a statement.

"Therefore, it is currently not possible to reliably predict what the (pollutant) level might be over the race weekend."

It said protective respiratory masks will be available for spectators "at cost price" while medical and first aid posts will be on standby "to handle any possible haze-related conditions".

Indonesian police said they have detained seven people whose companies are allegedly connected with illegal agricultural fires that have cloaked Southeast Asia in haze.

They could face up to 15 years in jail and heavy fines if found guilty of breaking Indonesian laws that ban starting forest fires.

Tens of thousands have fallen ill in parts of Indonesia as the haze thickened over the past fortnight, and the smog has led to bad air quality in Malaysia as well.

The situation has been made worse this year by an El Nino weather system, which produces tinder-dry conditions and increases the risk of fires.
Source: AFP