Sunnyside fire officials are investigating the cause of an anhydrous ammonia leak that caused the evacuation of an Alexander Road fruit warehouse for more than four hours Thursday.

Firefighters were called to DRR Fruit Products, 705 Alexander Road, after someone reported smelling ammonia in the area around 10:30 a.m., Sunnyside Fire Chief Ken Anderson said.

A refrigeration repair company was on site at the time of the incident working on the system, and alerted employees to the leak, Anderson said. An alarm system in the building activated, and the 30 employees working inside left the building, Anderson said. No one was injured.

Officials said the leak was contained to the building.

Members of the department’s ammonia leak team entered the building in hazardous materials suits and found that 950 pounds of the refrigerant had leaked and was isolated to a puddle on the floor.

Firefighters used fans to evaporate the puddle, and spent four hours waiting for ammonia levels in the building to dissipate from a high of 4,000 parts per million.

U.S. Occupational Safety and Health Administration standards limit workers’ exposure to no more than 50 parts per million in an eight-hour period.

Sunnyside’s Public Works Department shut off water and sewer service to the building to ensure that ammonia-contaminated water did not escape through the drains into the city systems, Anderson said.

He said ammonia may have gotten into water tanks inside the warehouse, and water would have to be disposed of properly. He said the state Department of Ecology was notified.

Records with the Department of Ecology show no previous ammonia releases at the site, department spokeswoman Joye Redfield-Wilder said in an email to the Yakima Herald-Republic. She said that DRR would work with the Port of Sunnyside to manage contaminated wastewater at the scene.

Firefighters left the scene about 2:30 p.m.

In addition to the public works department, the Yakima County Office of Emergency Management, Washington State Patrol and Sunnyside police assisted with the incident, Anderson said.

Representatives from DRR couldn’t immediately be reached for comment.

Anhydrous ammonia is a commonly used refrigerant in commercial food processors because it’s the most energy-efficient way to ensure cooling. It becomes a gas at minus 28 degrees Fahrenheit, and people exposed to it can have serious respiratory problems. Exposure can be fatal at high concentrations, according to the Centers for Disease Control and Prevention.