Flames engulf fabrication business in Bethlehem, Pa.

BETHLEHEM, Pa. (WPVI) -- Investigators are looking for the cause of a massive fire at a fabrication business in Bethlehem, Lehigh County.

The 3-alarm blaze started around 4:00 Wednesday morning on the 1100 block of Mauch Chunk Road at a business called Monocacy Fabricators.

At its peak the blaze created a blanket of smoke that covered parts of Bethlehem for hours, and reached as far away as Allentown.

Residents who live near the burning building were told they should stay inside.

It was around 10:00 a.m. when fire crews were finally able to get the flames under control and the shelter in place order was lifted.

At one point the power company cut service to 1,500 to 2,000 customers as a precaution due to the fire's proximity to power lines nearby.

The William Penn Elementary School was affected by the power outage and was closed for the day as a result.

Air tests are regularly being performed. So far, there is no indication of toxins or pollutants in the air.

Ryan Hay from the Northampton County Emergency Management explains, "The detectors looked for volatile organic chemicals, that goes down to the parts per million level. And again, that didn't pick up anything. But we can't definitively say that everything is absolutely safe. All out metering is telling us that there's nothing."

Authorities remain on the scene and continue to investigate what may have sparked the blaze.