A Philadelphia oil refinery experienced a fire that caused at least three massive explosions in Southwest Philadelphia around 4 a.m. this morning, reports. Thankfully four employees only suffered minor injuries that were able to be treated on-site, and the blaze is still burning though firefighters reportedly now have it under control.

Philadelphia Deputy Fire Commissioner Craig Murphy told reporters a vat of butane ignited and later exploded at the Philadelphia Energy Solutions Refining Complex, and the fire eventually spread toward fuel pipes, leading to more explosions.

Video of the explosions, via Global News on YouTube, shows the massive scale of the fireball:

A postal worker who witnessed the explosions claimed it was powerful enough to rock his truck, according to . Another witness taking video of the explosion could feel the heat from the fireball:

The Department of Public Health announced preliminary samples showed no significant risk of harmful air pollutants following the explosions. Here’s the full statement:

Air Management Services was on-scene immediately and took air samples. Preliminary testing at the refinery, and in the community around, found no ambient carbon monoxide, hydrocarbons (combustibles), or hydrogen sulfides.

Additional samples were taken and transported to the Air Management Services Lab. We are awaiting the results of the tests being run and will release the interpretation of the results as soon as it is available.

The Health Department has no findings that would point to any immediate danger in the surrounding community at this time, and the City is NOT recommending evacuation or shelter-in-place.

Some roadways were temporarily closed this morning to facilitate fire crews but have since been reopened. Over 120 firefighters responded to the three alarm fire, joining the refinery’s emergency response crews.

This was reportedly the second fire at the refinery this month, with a separate incident on June 10. At the time, there were following the fire, which was contained with no reported injuries.

The 150-year old refinery processes 335,000 barrels of crude oil per day, and is apparently the largest on the East Coast. Apparently the refinery is still operating at a reduced rate.