Worksafe WA is invetigating a dangerous occurrence involving the failure of a prefabricated aluminium stair unit.

The failure has allowed enough movement in a prefabricated stair unit for it to become dislodged from the supporting transom, resulting in a person falling approximately 10 metres to the ground below.

Inspections of other sites found prefabricated aluminium stair units with similar issues.

Download the CFMEU WA Alert on preventive measures for these units.