Visibility has been as low as 50 metres in the capital Bandar Seri Begawan
Brunei, whose territory shares Borneo with Indonesia and Malaysia, has been blanketed in a thick smoke haze since early in the year.
The origin of the haze lies not in the vast fires sweeping Indonesian territory away to the south-west, but in the flames destroying Brunei's own drought-stricken forests and those of the neighbouring Malaysian state of Sabah.
The resultant smog has forced the intermittent closure of Brunei's international airport, and for a two-week period, of local schools as well.
Visibility in the capital has frequently been cut to about 150 metres. With pollution readings set almost permanently above the hazardous level, sales of protective face masks and air purifiers are booming.
Alarm over the situation has prompted a significant number of expatriates, mainly dependent families, to leave the country.
Foreign diplomatic missions have taken action too, with the American embassy now deciding to allow its staff to go abroad for regular two week rest breaks. The embassy says it will continue to function normally and denies talk of a possible evacuation.
Sources at the British High Commission said families of staff members were recently offered the chance to go home but so far there had been no takers.
With fire-fighting efforts achieving poor results so far, the authorities are pinning their hopes in the rains. Muslims have been urged to hold special prayers for rain in mosques on Wednesday morning.