BLAST FRIGHT

A FLASH EXPLOSION caused by roach bombs and a lit pilot light was so powerful it sent a cat hurtling through the window of a Brooklyn apartment Thursday, authorities said.

The blast in a second-floor apartment on Hegeman Ave. near Amboy St. in Brownsville shattered two large windows and blew their frames to the ground at around 12:45 p.m. cops said.

Clinton Grant, 70, said he was about to leave the apartment with his son, his grandkids and their mother, when the explosion happened.

“It blew up,” said Grant, former super of the building. “All the windows blew out.

“I feel stupid,” he added, with a sheepish grin.

Grant insisted that he put nine bug bombs in the kitchen, but had not set them off.

But police said a man in the apartment activated the roach foggers without disabling the pilot light, causing the flash explosion.

Tyrone McClean, 41, who lives on the same floor, said the explosion “ranks right up there” with the craziest things he’s witnessed in the building.

“Sounded like someone kicking down a door,” McClean said. “I didn’t see any flames. Just an explosion.”

Two people suffered serious injuries and two sustained minor injuries. A 3-year-old girl and an 8-month-old boy were among those hurt. Medics took them to Brookdale Hospital.

The force of the blast propelled the family pet — a cat — out of a window. The flying feline was killed instantly.

Grant said he was trying to exterminate the 100 cockroaches who had in taken up residence in his apartment.

“I wanted the fumes to fill up the kitchen,” he said.

People who live in the building said they suspected the oven or stove may have been on in Grant’s flat.

According to the Environmental Protection Agency, bug bombs usually contain aerosol propellants that shoot the contents out at once to fumigate an area.

Those substances are flammable, so the agency advises people to keep them away from flames, lit pilot lights or sparks from electrical appliances that cycle on and off like air conditioners and refrigerators.

Foggers should be placed 6 feet from ignition sources, the EPA said.

One six-ounce fogger is enough to treat a 25-by-25 foot room, the agency said.

Two dozen people were injured when a blaze sparked by bug bombs, ripped through a Chinatown building in July 2013.

The fire started in a beauty salon on Pike St. and spread to apartments on the upper floors.