The Hong Kong Construction Association on Tuesday issued its own guidelines aimed at preventing heatstroke among people who work outdoors, saying the government's own advice is so complicated it's almost impossible to follow.

However, the alternative advice appears to leave workers with a lot less time to escape from hot weather.

Guidelines the Labour Department issued earlier this year were accompanied by a three-tier heat warning system and advise breaks of various lengths, depending on how strenuous an employee's work is.

The association still wants to make use of the heat warning system, but has one piece of advice for all outdoor workers under each signal, irrespective of how intensive their job is.

If the "amber" signal is up, the association recommends workers be given a 15-minute break sometime during the morning, an extra 15 minutes for lunch, and then a 15-minute break in the afternoon.

The breaks should be 30 minutes under a "red" warning signal, while work should stop completely under a "black" signal – with both these signals expected to be quite rare.

Under the government's guidelines, however, workers other than those carrying out the lightest of duties should get breaks of between 15 and 45 minutes every single hour, under even the lowest signal. The threshold for downing tools altogether also comes under the "red" signal for some workers, rather than "black".

With no fixed time for the suggested break under the association's advice, it's not clear if workers would get any extra rest at all if the warning signal was retracted before they got round to getting out of the sun.

Despite recommending the same action be taken by all workers when a heat warning is issued, the association said employers may still decide to give those with heavier duties longer periods of rest.

"The site personnel or the safety officer needs to carry out risk assessment... They may increase the rest time for the heavy workload workers carrying out work that day," said the association's vice-president Conrad Fung.

"On the other day, there may not be any heavy workload work carried out on-site. They may simply follow the guideline, the resting time recommended."

Last week, environmental campaigners and a grassroots advocacy group also said the government's guidelines are too complicated, but mainly focused their complaints on the heat warning system.

Greenpeace and the Hong Kong Workers' Health Centre said it would be easier for firms if they instead took action based on the observatory's general hot weather warnings, noting that these don't tend to be issued and retracted as quickly as the new heat signals.