Singapore enveloped in a thick pall of wood smoke caused by forest fires in Sumatra . Pollution index reaches 371 on Wednesday , the worst level since 1997 when it reached 226 . National Environment Agency says air quality becomes 'very unhealthy ' when the index passes 200 . Comment:
Singapore enveloped in a thick pall of wood smoke caused by forest fires in Sumatra . Pollution index reaches 371 on Wednesday , the worst level since 1997 when it reached 226 . 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 an estimated $ 9 billion .