In 1997, the three-hourly Pollution Standards Index (PSI) reached as high as 226. The highest PSI over a twenty-four hour period, however, was 142, recorded in 1994.

Readings of below a hundred are considered safe. This reduced visibility to a few hundred metres, compared to up to twenty kilometres on a clear day.

The PSI measures sulphur dioxide, nitrogen dioxide, carbon monoxide, ozone and suspended particles. The pollutant which registers the highest reading on a scale of zero to five hundred in a twenty-four hour period is taken as the reading for that period.

The causes of the haze are manifold.

One cause is the sumatras, which are caused by the strong southerly winds blowing from central and southern Sumatra. These same winds carry the thick smoke clouds from forest fires to Singapore.

The fires, in turn, are the result of indiscriminate land clearing, either by shifting cultivators (who account for only a fifth of the fires started) or by industrial timber and agricultural plantations.

For every hectare logged, fifty cubic metres of meranti and tembusu are removed (the wood is used for furniture and in construction). Up to seventy cubic metres of other species ends up as waste wood when the area is cleared to set up a plantation. There is little incentive to process this waste wood into chips for the paper, pulp and plywood industry because the latter is protected.

Some of the forest fires are also sparked by peat seam fires igniting the surrounding bush in the dry season.

Peat is decomposed vegetation, representing the first stage of coal formation. Among the many impurities in the peat are highly combustible sulphur and hydrogen. The sizes of the seams range from a few square metres to more than two hectares.

Because of their size and the fact that they are not more than four metres underground, the peat seams serve as heat conduits, fed by oxygen from the thin porous topsoil, starting fires hundreds of metres away from the source.

From the surface, they look like barren, hard earth, pockmarked with craters. They emit heat and smoke but no flames. Some of them have been burning since the last severe drought of 1982/3!

Part 2: Some Measures Taken

Reproduced with permission from the site formerly known as 'No Place Like Home', © Kenneth Y T Lim 1995-9