The Centre for Health Protection (CHP) on Sunday said people should only use gas water heaters in well-ventilated areas. It made the comment after a 56-year-old man, and two of his family members, were hospitalised on Saturday with carbon monoxide poisoning after he took a shower.

All three were sent to Yan Chai Hospital. The man was later transferred to Pamela Youde Nethersole Eastern Hospital. His two family members, including a 13-year-old, were discharged.

The Electrical and Mechanical Services Department (EMSD) also reminded people to only use gas water heaters which have a 'GU' mark, meaning they have been approved by the department.

In a statement, the government said all windows in the apartment were shut and the exhaust fan had not been turned on. An on-site inspection conducted by the Electrical and Mechanical Services Department showed that the flueless gas water heater at the home was not suitable to be used in bathrooms. The heater model also lacked approval from the EMSD.

The EMSD has seized the gas water heater. It will investigate whether any person has contravened the Gas Safety Ordinance.

The CHP said that carbon monoxide is a colourless, odourless and tasteless gas which is a by-product from incomplete combustion of any fuel which contains carbon, such as wood, natural gas and gasoline.

Exposure to a low concentration of carbon monoxide can lead to a range of symptoms such as dizziness, headache, tiredness and nausea. Exposure to a high concentration of carbon monoxide can lead to impaired vision, disturbed co-ordination, unconsciousness, brain damage or even death.