Three family members – a grandfather, a father and a son – were seriously injured on Tuesday when a mobile home exploded in Massachusetts.

The incident occurred around 3:30 p.m. Tuesday in Peabody. Firefighters responded to reports of an explosion and found the RV engulfed in flames. Three men were conscious and alert but had suffered severe burns.

Two of the men, one in his 40s and one in his 70s, were flown by rescue helicopter to Massachusetts General Hospital in Boston to treat their burns, according to Peabody Fire Chief Jay Dowling. Another man, in his 20s, was taken by ambulance to a nearby hospital.

There is no update on their current condition, but each of the men was described as alert and responsive.

The fire was extinguished before it could spread to surrounding houses, but the siding of the house in front of which the car was parked was melted by the intense flames.

Investigators concluded that the men may have been working on the vehicle at the time of the explosion. However, the exact cause of the explosion is still unknown.

Witnesses told WBZ-TV that the three men were preparing the RV for a trip to the Grand Canyon when the explosion “shook the entire neighborhood.”

A doorbell camera recorded the explosion and the ensuing fire and showed one of the men rolling around burning, the broadcaster reported.

“It could have been worse. Yes, there could have been fatalities. It could have spread to the houses, so it was a great blow for the firefighters,” said Peabody Fire Chief Jay Dowling.

Peabody is located about 20 miles north of Boston.