Calderdale firefighting crews were among scores of firefighters battling a blaze in Rawdon into the early hours.
It started yesterday afternoon at Airedale Air Conditioning on Leeds Road.
Thick smoke was visible across the city and roads were closed.
Arond 20 crews and 100 firefighters were mobilised.
There is no firefighting currently and at 8 am today two crews were still at the scene monitoring the site.
West Yorkshire Fire Service said it was a very significant blaze but it hoped a large part of the site could be saved.
It is not known at the stage what caused the blaze.