A Christmas grotto manufacturer was one of three businesses hit by a "severe" fire on an industrial estate. More than 70 firefighters were sent to Clearwater Industrial Estate, in Wolverhampton, on Tuesday evening.
Staff working at one of the companies on site - which include an archive service and a plastics firm - alerted emergency crews.
Ettingshall Road was closed while crews dealt with the blaze, which caused part of a roof to collapse. One unit was completely destroyed along with two vans.
West Midlands Fire Service said crews managed to contain the fire and stop it spreading to two other businesses.
Pubic Health England (PHE) issued the advice after flames ripped through A.S.H Plastics and Archive Services at the Clearwater Industrial Estate in Ettingshall Road overnight.
The government agency said the risk to health was low but encouraged anyone who has not been evacuated from the local area to keep doors and windows closed and to leave any ash or debris from the blaze alone. Anyone with debris on their lawn should avoid mowing it until it has been removed, and wreckage should not be vacuumed or swept in case of creating airborne dust.
Wolverhampton Council has commissioned specialist cleaning contractors to clean up the area. Residents finding ash or debris from the fire on their property were advised to leave it alone and to contact the council on 01902 551 155 to arrange a clean-up.