On Wednesday evening, a potassium cyanide leak in a Czech laboratory injured a member of staff, a spokesman for the fire department, Martin Kavka, reported.
"A leakage occurred during the work with the poisonous substance which had to have been destroyed. A chemist got an arm injury and was taken to hospital," he said.
A special ventilation system was automatically activated in the laboratory, thus there was no imminent threat to the environment, according to Kavka.
The area around the laboratory was cordoned off by the police during the operation, which had been concluded by Thursday morning.
In March, Prague witnessed a blast at a Unipetrol plant 30 km (19 miles) north of the city that killed six people.