About 100 staff were evacuated last night from paint and coatings company PPG on Huddersfield Road, Birstall following an ammonia leak.
Cleckheaton fire crew commander Adrian Murphy said the incident was reported to them at 9.15pm.
He said: “We had to send in five firefighters in breathing apparatus with specialist monitoring equipment to ascertain the nature of the leak.
“It appears that there has been a mechanical failure somewhere in the plant.”
Ammonia is a potentially dangerous substance. Its vapours can be explosive and it can pose a threat to the environment so needs to be handled with great care.
Mr Murphy added: “Once we had established there was no threat to life we left it in the hands of a specialist repair team from Manchester.
“We were there for three and a half hours and it was a successful, smoothly handled operation.
“The spillage was contained on site but how much ammonia was leaked it is hard to say.”
A PPG spokesperson said "PPG's Birstall paint manufacturing facility was evacuated on Wednesday evening as a precaution after an alarm in the facility was activated. Local authorities responded as a precaution, however, the site has since returned to normal operations."
