The haze may appear to have eased, but companies are putting workers' health first, even at the risk of failing to fulfil contracts.

Bosses of construction, cleaning and landscaping companies told The Straits Times yesterday that they hope customers will understand and bear with reduced services if the air quality worsens.

"Cleaners can continue to do the important tasks like clearing rubbish bins, but clearing fallen leaves can be left for another day," said Mr Sunny Khoo, sales director of Clean Solutions. His firm provides cleaning services at public and private housing estates.

He said: "We hope clients and residents won't complain if they see more rubbish around than usual."

Mr Woon Chiap Chan, country managing director of ISS Facilities Services, which employs about 250 workers to do outdoor landscaping, cleaning and pest control, said customers have been understanding so far when told that workers may have to avoid non-critical work, such as sweeping outdoor compounds, for a couple of days.

"But if it's prolonged - for one or two weeks - then it will be a headache as we may be penalised," he said.

At 5pm yesterday, the 24-hour Pollutant Standards Index (PSI) was at 98-118, between the high end of the moderate range and the low end of the unhealthy one.

Many firms have put in place measures to protect staff who work outdoors.

At a Braddell Road construction site, environmental control officer Ganesh Kumar checks the National Environment Agency's website every hour for the PSI levels.

If the PSI goes above 200, he alerts supervisors across the site.

Said Mr Ganesh, 25: "We brief workers about the haze at two meetings every day, and also monitor those with breathing problems, and arrange for them to do work in the storerooms or office."

CHL Construction safety officer Richard Teo said that he updates site supervisors every hour and would suspend non-essential outdoor activities if the three-hour PSI goes past 200.

At Lum Chang Building Contractors, older workers and those with asthma have been redeployed to work indoors where possible, while at BD Cranetech, workers have been encouraged to have lunch in air-conditioned places and not to stay outdoors for more than 10 hours.

Workers at sites The Straits Times visited yesterday were not wearing masks, although they said they had been supplied with them. Most did not think the haze was bad enough to warrant wearing the masks.

Mr Syed Amrul, 27, a supervisor at a site in Toa Payoh, said he was too busy to get his mask, which he left in the storeroom. He said the haze gave him a headache on Monday, but that he has since felt better.

He said: "I took some medicine, but I didn't see the doctor because I thought it was a small matter."

Another supervisor in Toa Payoh, Mr Chew Hock Hwee, 54, said his team of men did not want to wear masks as they were tarring the road.

He said in Mandarin: "It is very hot work, so the masks are uncomfortable. Of course, if the PSI goes over 200, we must let them rest."

• Additional reporting by Priscilla Goy