Emergency services attended, but the worker died.
"We are deeply saddened by the loss of our colleague in the close-knit community of Kalgoorlie," Monadelphous managing director Rob Velletri said.
"We extend our sincere condolences to our employee's family, friends and colleagues during this very difficult time."
An investigation is underway.
Monadelphous is providing support to the worker's family and colleagues.
The company's maintenance and industrial services division has worked in the Goldfields for over 20 years for clients including BHP Nickel West.