A hospital gas leak could have been much worse if the escaped gas had ignited – showing why Zone 2 equipment can be a sensible precaution even if gas is supposed to remain contained within a pipeline.

Although there are no formal definitions on the classification of hazardous areas as Zone 0, 1 or 2, the HSE suggests a Zone 2 classification should be applied where there is an explosive atmosphere for less than 10 hours per year, but still with enough likelihood to need precautions.

Catastrophic events like a broken gas pipeline are typically outside the scope of this kind of assessment; however, it is sensible to use Zone 2 equipment anyway if there is any likelihood of a short-term leak.

Such a leak occurred in January 2014 at what is now Royal Stoke University Hospital (formerly the University Hospital of North Staffordshire).

A construction contractor was installing new drainage and a new car park, when an excavator’s bucket hit a buried gas pipeline, releasing large quantities of natural gas.

The leak lasted for 90 minutes, the hospital’s energy centre had to switch to an alternative oil heating supply, an exclusion zone was set up and the main road across the hospital grounds had to be closed.

HSE inspector Andrew Bowker pointed out though that the situation could have been much worse.

He said: “The result was a highly dangerous situation that had the potential to expose construction workers, hospital staff, patients and visitors to an initial flash fire and subsequent fire and explosion risk.”