Hazardous materials workers on scene after the blast. Photo credit: OnScene.TV

A 5-gallon propane tank fueling a portable grill caught fire and exploded Thursday afternoon in Kearny Mesa, injuring three people.

The explosion happened about 12:45 Thursday during a corporate event held on a patio to welcome the new CEO of Cubic Corp. at the company’s Balboa Avenue headquarters in the Kearny Mesa neighborhood of San Diego.

Two of the critically injured people, who both sustained third-degree burns, were employees of the catering company brought in for the event. According to OnScene.TV, they were taken to the UCSD Burn Center for treatment.

A Cubic contractor with less serious burns to his hand and face refused any medical help.

Fire damaged the grill and surrounding patio area, including melting awnings overhead. A leak is suspected as the cause of the tank explosion, according to OnScene.TV.

The San Diego Fire-Rescue Department and the county’s Hazardous Incident Response Team are investigating.