Companies Sapec Quimica, Boat Centre and Sopac, all located on the Mitrena Setúbal industrial estate where the fire occurred, temporarily shut their doors to the public on Wednesday on the advice of the Civil Protection Service.
The recommendation was reportedly made after a change in wind direction and a rise in temperature threatened to spread the lingering toxic smoke further around the area.
A 60-metre area within the warehouse affected by the blaze was covered with sand, which according to a spokesperson for the local fire-fighters was the best way to fight the flames in this case.
The fire ignited on Tuesday in a warehouse belonging to Sapec, where “abrasive and toxic” sulphur products were stored.
As a result local schools were closed for the day due to concerns that the smoke arising from the fire could have harmful effects on health.
Residents in the vicinity of the industrial estate were instructed to stay inside their homes as fire-fighters tackled the noxious flames.
Three people were treated at a local hospital due to problems caused by the smoke, while six fire-fighters were injured in the operation.
Air quality was confirmed back to normal by Tuesday night, according to the Portuguese Environment Agency (APA), which explained that the fire caused Sulphur dioxide to be released into the air, adding that due to the wind direction a cloud of toxic smoke was pushed north, over the Sado Estuary Nature Reserve and up to Vila Franca de Xira.