A 51-year-old man has died of injuries sustained in a boiler explosion at a plant that heats the Parliament Buildings.

A hazmat team from the Office of the Ontario Fire Marshal entered the heating plant to monitor its air quality a day after an explosion there. (Rebecca Zandbergen/CBC)

The man had suffered second-degree burns to 60 per cent of his body, paramedics said at the time of the explosion.

Police confirmed the death Tuesday, a day after the noon-hour explosion at the century-old heating plant behind the Supreme Court of Canada. The man's identity has not been released.

Another man received first-degree burns in the blast while a third had minor injuries. Most of the other 20 or so employees at the plant were not hurt.

The Cliff Street plant supplied heat via underground pipes to 52 buildings in Ottawa's core, along Wellington and Sparks streets and as far away as the Byward Market and the headquarters of the Department of National Defence on Colonel By Drive.

On Tuesday, a mask-wearing hazmat team from the Office of the Ontario Fire Marshal entered the building to monitor its air quality as grim-faced plant employees stood outside.

The building has been declared structurally sound. However, concerns remained about the effect of the explosion on asbestos wrapped around the pipes inside. Wayne Romaine, spokesman for the fire marshal's office, said crews will also be checking levels of carbon monoxide and hydrogen sulphide.

The Technical Standards and Safety Authority, the Ontario agency that licences boilers, was also on the scene investigating Tuesday.

Investigators said they hope the power to the plant will be turned back on at some point so they can download data from the plant's computers.

As of noon, Public Works and Government Services Canada had not yet commented on the incident.

On Tuesday, the plant was offline and heat was being supplied to the affected buildings from a plant at the Government Printing Bureau in Gatineau.

In a memo to Parliament Hill staff, a senior official at the House of Commons said the explosion's impact on employees working in the buildings would likely be minimal, as outdoor temperatures remain mild. A high of 14 C was predicted Tuesday by CBC climatologist Ian Black.