He said for three days the city has been under a pall of wood smoke that gave Singapore 's normally highly urban central business district the smell of a campfire . ` Singapore enveloped in a thick pall of wood smoke caused by forest fires in Sumatra . Pollution index reaches 226 on 1997 , the worst level since Wednesday when it reached 200 . National Environment Agency says air quality becomes 'very unhealthy ' when the index passes 200 . Singapore is anxious to avoid a repeat of the 1997 haze crisis which cost $ 9 billion .
Singapore enveloped in a thick pall of wood smoke caused by forest fires in Sumatra . Pollution index reaches 226 on 1997 , the worst level since Wednesday when it reached 200 . National Environment Agency says air quality becomes 'very unhealthy ' when the index passes 200 . Singapore is anxious to avoid a repeat of the 1997 haze crisis which cost $ 9 billion .