Johannesburg - The substance found in an envelope at Sanral's headquarters in Centurion, Pretoria, was not dangerous, the roads agency said on Wednesday.

“Upon investigation, the white substance was found to be harmless,” SA National Roads Agency Limited CEO Nazir Alli said in a statement.

“Our priority was to ensure the safety of the people working in the building. They received trauma counselling for the anxiety caused by this incident.”

Alli did not say what the powder was. The Tshwane hazardous material unit was called to Sanral's offices on Tuesday afternoon after the substance was found on the premises. The building was evacuated and its electricity shut down.

Thirty-seven people were decontaminated and hospitalised as a precaution. All of them had been discharged by Wednesday morning.

Alli said the evacuation did not compromise the toll collection process and toll gantries remained operational.

“The call centre was however affected due to the evacuation of staff but is currently operating at full capacity.”

Sanral said it was co-operating with authorities to find the perpetrator. - Sapa