The NI Health and Safety Executive (HSENI) said it responded to more than 600 emergency calls after the deaths of two Newtownabbey teenagers in a suspected carbon monoxide leak.
Aaron Davidson and Neil McFerran, who were both 18, died at an apartment in Castlerock in August.
Another friend, Matthew Gaw, had to be taken to hospital.
The HSENI subsequently asked people who had work carried out by George Brown - trading as George Brown of 'The Calor Shop' in Coleraine - to switch off all their gas appliances immediately.
They were also asked to contact HSENI's emergency helpline number.
The BBC has learned that in the month after the HSENI set up the helpline it responded to 603 calls specifically relating to the safety alert.
It has declined to give any details of the calls, or how they responded to them, citing the ongoing police investigation.
The HSENI said the 'The Calor Shop' was an entirely separate legal entity to Calor Gas (NI) Limited.