An investigation is underway after three workers suffered chemical burns at Alcoa's alumina refinery in Pinjarra.
Emergency crews, including multiple ambulances, were called to the refinery around 5.20pm on Tuesday.
An Alcoa spokeswoman said the men's burns were a result of a valve failure.
"A valve failure at Alcoa’s Pinjarra Alumina Refinery resulted in three employees being exposed to process material,” the spokeswoman said.
Two of the men had to be airlifted to Fiona Stanley Hospital due to the severity of their burns while the third man was treated at the refinery.
It is understood the chemical was sodium hydroxide, also known as caustic soda.
“The area in question has been isolated and clean-up of the material has commenced," the spokeswoman said.
“An investigation into the cause of the incident is underway and the Department of Mines, Industry Regulation and Safety has been notified.”
Mandurah Crab Fest boasts huge range of free, family friendly entertainment
Fuel prices surge in Perth, Mandurah
Teen boys charged over Mandurah burglaries
Tragic update in search for missing man Robert Snyder
Premier Roger Cook to leave Kwinana electorate, move to Perth
Mandurah Marine Rescue's new vessel named in memory of nun who survived 1959 boating accident
Teen dies in motorbike crash at Waroona Dam
Shark alert issued after whale carcass reported at Preston Beach
Kwinana businesses to refuse serving students during school hours