The Health and Safety Executive (HSENI) has said it is conducting a "robust, criminal investigation" into the deaths of two teenagers in Castlerock.
Neil McFerran and Aaron Davidson died in a holiday apartment last week from suspected carbon monoxide poisoning.
In a statement this afternoon, deputy chief executive of the HSENI, Dermot Breen, said it was doing all it could to safeguard public safety.
The investigation has centred on George Brown of the Calor Shop in Coleraine.
The PSNI has said detectives are working alongside the HSENI in relation to the deaths.
The HSENI has advised anyone who has had a gas appliance fitted by Mr Brown to switch if off.
On Wednesday, two businesses were temporarily closed for safety investigations.
Mr Brown's solicitor, Garret Green, said his client had worked in many premises.
He added: "Mr Brown has not received any direct contact from the HSE in regards to the number of places which are under investigation.
"For arguments sake, Mr Brown estimated that he would have been effectively responsible for 108 businesses premises in the area out of approximately 115.
"He has been in the area for the last 20 years and is highly respected, his customers are people he lives amongst in his community."
The Calor Shop run by Mr Brown is an entirely separate legal entity to Calor Gas (NI) Limited.
The premises was searched by the authorities on Tuesday night.
Mr Green said that his client is anxious that the proper investigations are carried out to ensure the saftey of all of his customers.
"The caveat is that he is anxious the matter is investigated as dilligently and expeditiously as possible and to that end there is some finality, at the earliest possible opportunity, to allow him to continue with his livelihood."
Aaron and Neil, both 18, from Newtownabbey outside Belfast, had been spending time at the apartment awaiting their exam results when they were overcome by poisonous fumes last week.
A third teenager, Matthew Gaw, also 18, survived the leak.
The HSENI found that a liquefied petroleum gas appliance inside a flat at Tunnel Brae Court had not been working properly.
On Wednesday, the Ice House Restaurant in Portstewart and the Village Caff, Rasharkin, were closed so they could be examined by Health and Safety Executive staff.
The Ice House opened again on Thursday.
Meanwhile, Finance Minister Sammy Wilson has said he will look at the possibility of making carbon monoxide alarms compulsory for all newly built homes.