They arrived shortly after 10:30 to find people leaving the building and immediately set up a triage area upwind to assess people, ER24 spokesperson Werner Vermaak said.
A hazardous materials unit searched the building and found a man lying under a table, but he had died.
Colleagues suggested he may have become confused during the evacuation, or was overcome by the fumes.
It was believed that construction work to the roof led to the rupture of an ammonia gas line.
Five paramedics had also been taken to hospital for treatment as they began showing symptoms of exposure to the gas.