A Turners & Growers spokesman said the spill occurred when packaging company Viscount FCC, which shares the site, was washing a crate.
The substance, called "Principal", was widely used for cleaning equipment in a range of industries across the country and active ingredients included sodium hypochlorite and sodium hydroxide, the spokesman said.
"Emergency services were alerted immediately and the fire service has contained the spill and is taking appropriate steps for safe clean-up and disposal of the chemical," he said.
"All T&G staff were evacuated from its building as a precaution, but following assessment of the building, have now returned to work."