Around 30 workers were evacuated from a South Staffordshire chip factory today after liquid ammonia leaked inside.

Engineers doing maintenance work on machinery at the McCain factory in Wombourne accidentally hit a pipe to an ammonia reserve tank and caused the leak.

Five crews of firefighters and Staffordshire’s chemical response unit rushed to the factory on the Heath Mill Road industrial estate at around 6am as ammonia started leaking into the site.

Firefighters wearing chemical suits spent hours monitoring levels of ammonia in the air.

It is believed workers would be let back inside the factory later today.

Assistant area fire commander Mick Jahn said: “There were some maintenance engineers inside the ammonia tank room and as a consequence of the work a one inch pipe leading to the reserve ammonia tank was fractured. It was not the main ammonia tank. The reserve tank contains around eight litres of liquid ammonia and the factory’s emergency team put all of the procedures in place to isolate the leak and get all of the workers out before we arrived.

“They did a fantastic job and our presence was very much precautionary.

“Firefighters in chemical suits ventilated the area and have been using portable gas monitoring equipment to check the levels of ammonia in the air.”

A McCain spokesman said no workers were put in any danger.