The fire that injured three people and destroyed a Falafel Bus food truck on H Street on Wednesday was caused by an employee refueling a gas generator while the truck was on and while food was being served in the truck, The Washington Post reported Thursday.

The fire started on the outside of the truck and then spread quickly when it reached the inside because of the fuel feeding the stoves inside the food truck, The Post reported.

Safety guidelines for food trucks stipulate that the gas should not be refueled while the truck’s engine is still running or while food is being served. A representative from D.C. Fire and EMS told The Post that the workers should at least turn off the truck and allow it to cool down before refilling the gas tank, but the driver should ideally drive the truck to a gas station to refill it.

Three truck employees, two women and one man, were taken to MedStar Washington Hospital Center, according to The Post. One patient was in critical condition Wednesday.

“Improper fueling is now believed the very likely cause,” Doug Buchanan, a spokesman for D.C. Fire and EMS, told The Post.

A student created a crowdfunding campaign for the people injured in the food truck fire the day the fire happened. The campaign raised more than $8,000 as of Friday.