Raleigh, N.C. — A sulfuric acid leak at a north Raleigh pharmaceutical products plant prompted authorities to urge nearby residents to stay indoors Thursday afternoon.

The last of the Hazmat trucks left the Mallinckrodt Chemical plant at 8801 Capital Blvd., and the situation was clear and under control around 6:30 p.m. Thursday, authorities said.

Now the focus, at least for the company, is how it all started.

Fifteen thousand gallons of sulfuric acid leaked from a storage tank at the North Raleigh facility.

Employees discovered the leak at 7:05 a.m. Thursday morning, but it took more than 11 hours to remove the excess acid. Part of the problem, according to firefighters, was that they had to wait for special pumping trucks to arrive from Greensboro.

Overall, crews said all safety procedures worked properly. The sulfuric acid was contained to a small area near the back of the facility, but the main concern was the weather.

The spill caused no immediate injuries, and there were fewer people at the plant than normal, about 140 people total. The plant was previously scheduled to be in shut down mode this week, according to plant officials.

Even with fewer people around, authorities feared the prospect of rain Thursday afternoon reacting with the acid to produce toxic fumes.

As a precaution, two Wake County Schools, a preschool and at least one business were forced to evacuate. Residents in a nearby apartment complex were told to stay inside.

Mallinckrodt also sent home all non-essential personnel as a precaution, said Kathy Akroyd, a spokeswoman for the state Division of Waste Management, which responded to the spill.

By Thursday evening's rush hour, things started getting back to normal. Businesses re-opened and residents were told they could go back outside.