Construction firms are hoping that the haze will be a short-term blight, even as they take measures to protect the health of their workers and business.

Industry players said that they foresee the impact the choking smog will have on their business if the Pollutant Standards Index (PSI) reading hovers around historical highs as it has done this week.

These industry players were, however, unable to put a specific dollar cost to all this bad air.

Ho Nyok Yong, president of the Singapore Contractors Association (SCAL), said that the timing of the haze came as a surprise, as it has in recent years tended to happen later in the year.

"This haze is very unwelcome, timing-wise anyway; it doesn't help the industry," he said, in a reference to contractors already having to fall in with a tightened man-year entitlement quota, which allots to each main contractor a quota of foreign construction workers for a specific construction project.

Lee Yeow Koon, managing director of BK Civil and Construction, said that work schedules could be pushed back by "a minimum of 20 per cent". He has asked for an extension for his project deadlines but knows that he will not be able to get all of the companies to agree.

Thomas Bon, chief executive officer of property company OKH Global, expects a cushioned blow, because he has adopted newer construction methods and is using precast materials for his construction arm. These practices require fewer workers on the ground. He added: "And because I am also a developer, the impact (is) slightly lesser."

But he is hoping the haze will linger for no more than a week. "Anything more than that, I think it's going to be disastrous."

The companies are aware of their contractual obligations, and that the kind of work they do outdoors makes them vulnerable to losses if the government issues a work restriction order. If the poor air quality persists, they may have fewer workers on site.

Kenneth Lim, assistant director of Swee Hong, said that if a work restriction order is issued, the business will not be the only one to suffer - workers on a daily wage will also suffer. "Because once (you) stop work, they get no income."

These companies are not letting bottomline concerns undermine their workers' health and safety.

Swee Hong and BK Civil and Construction have already suspended some outdoor work; OKH Global has halted overtime work, an industry norm, for its construction arm since Tuesday. All have provided their workers with face masks.

Mr Lim from Swee Hong does not rule out stopping work entirely today.

Dr Ho said that SCAL has been sending out circulars to keep its more than 2,500 members informed of the latest developments, and advised them to take the necessary safety measures.

"We hope this haze quickly goes away - not just (for the) construction industry. I think for Singapore, all the citizens and all the workers and visitors to Singapore."