Three workers died and seven others were injured after a combustible dust explosion at an industrial building in Tuas, Singapore Thursday.

Five of the injured were in critical condition according to Silas Sng, commissioner for workplace safety and health and director of the Manpower Ministry’s Occupational Safety and Health Div. Sng reported that the other two workers were released.

The building is occupied by Stars Engrg, a company that deals with fire protection systems. 

Sng said that the explosion was caused by potato starch powder that was in a confined environment. He also explained that the dust is generated when powder is transferred, such as from a bag into a mixer. “Over time, the dust can accumulate in the environment, especially if the ventilation or the housekeeping is inadequate," said Sng. "And when the dust comes into contact with a source of a friction, an explosion will occur as we see in this accident.”

The source of ignition that sparked the explosion was not specified.

The Workplace Safety and Health Council has called for a "safety time-out" so employers can assess their business processes and make sure all machinery is properly maintained and used.

The identities of the deceased had not been relased. The Ministry of Manpower was conducting a full investigation.