WASHINGTON — A section of the Smithsonian National Zoo will remain closed for the rest of the day after a possible chlorine release Thursday morning. The American Trail area of the zoo, which is home to North American species like ducks, pelicans and wolves, was closed shortly after 11 a.m. so D.C. Fire and EMS crews could investigate. The fire department determined the outdoor areas were safe for staff to return about 2 p.m. However the trail won’t reopen to the public until Friday morning, the zoo said in a statement. According to the zoo, a contractor was working in a mechanical room that houses water treatment and filtration equipment near the beaver and otter exhibits when he detected the strong odor of chlorine. The contractor left the room and then heard a loud bang, said zoo spokeswoman Devon Murphy. There was no smoke or fire. Zoo officials believe there was a chlorine emission, Murphy said. Chlorine is used in the water filtration system at the zoo. The contractor was not hurt, nor were any staff, visitors or animals, zoo officials say.

Contractor working in utility area reported “chlorine incident” near beaver/otter exhibit @NationalZoo no one hurt pic.twitter.com/wUaciJF3uU

— Kate Ryan (@KateRyanWTOP) March 17, 2016

DCFD gave all clear for staff to check outdoor animal habitats on American Trail. Animals accounted for &doing well pic.twitter.com/kvU293Tfd1 — National Zoo (@NationalZoo) March 17, 2016

WTOP’s Kate Ryan contributed to this report.