PITTSBURGH — A chemical reaction while cleaning a clogged sink led to the evacuation of a Pittsburgh nursing home.

According to Allegheny County emergency officials, maintenance workers at the Oakmont Center for Nursing and Rehabilitation facility were putting drain cleaner into a clogged slop sink when there was a chemical reaction and it started fuming around 3 p.m.

The chemical explosion was described by a nurse as a “blast.” The 76 residents in the home were evacuated.

The nursing staff told WPXI-TV that all of the residents were safe. One staff member was treated at the scene.

Two Port Authority buses were brought in as temporary shelter. The Salvation Army was also called in to assist.

The facility put its “mass casualty” plan into action, as first responders from nearly every surrounding town rushed to help. Officials said the plan paid off, as no one was seriously hurt.

Hazardous materials crews worked to ventilate the facility, and residents were allowed back into the building Thursday night.

County officials told WPXI-TV the facility is regulated by the state, and this incident will be investigated.

The facility has an overall 2-star rating, which is below average, based on health inspections, staffing and quality measures, according to the Medicare.gov Nursing Home Compare website.

Inspection reports through the Pennsylvania Department of Health website show seven inspections at the facility this year, following several complaints.

The facility was cited following an inspection in January 2020 for failing to thoroughly investigate and report possible abuse.

The last inspection was for a complaint at the end of April, but the facility was not cited at that time.