Employers in Northern Ireland could face legal action if they fail to protect their workers from passive smoking, a cancer charity has warned.
The charity said employers should know risks of second-hand smoke
The Ulster Cancer Foundation, in conjunction with the charity, Ash, has said all employers should now be well aware of the health threat posed by smoke.
In a letter to the trade, they warn that a so-called "date of guilty knowledge" - at which point no employer should be unaware of the potential health damage caused by passive smoking - has long past.
This fact, it says, renders any employer not taking steps to protect staff liable to court action under the 1974 Health and Safety at Work Act.
Ash has teamed up with a firm of personal injury lawyers and plans to use the letters as evidence in any future court action.
The Ulster Cancer Foundation is campaigning for clubs and restaurants in Northern Ireland to be made smoke-free zones to protect staff.
Gerry McElwee of the Ulster Cancer Foundation said second-hand smoke was a major health hazard and employers should have known of the risks by the early 1990s at the latest.
"In the event of claims for compensation for health damage, employers will be expected by the courts to know of the health effects of exposing employees and others to second-hand smoke and to take reasonable steps to eliminate it," he said.
Restaurants in the Republic of Ireland will become smoke-free zones
He said second-hand smoke contained more than 4,000 chemicals, including benzene, formaldehyde, arsenic, ammonia and hydrogen cyanide.
"The US Environmental Protection Agency has classified environmental tobacco smoke as a known human (class A) carcinogen," he added.
"This has been confirmed by research from numerous respected organisations world-wide."
Lung cancer is Northern Ireland's biggest cancer killer, with 850 people diagnosed each year.
Smoking is to be banned in all workplaces in the Republic of Ireland including pubs, restaurants and hotels, from 26 January.
The hospitality industry is opposed to a complete ban in the north, saying it is already improving air quality in pubs and bars.
Last year representatives from all 13 Royal Colleges of Medicine called for a ban on smoking in public places, saying the move could save 150,000 lives.