Update -- July 18, 11:15 a.m.:

BCoPD fire investigators have determined that Tuesday's explosion in the 4200 block of Twin Circle Way, 21227, was accidental. A contractor working in the home was refinishing a bathtub when chemicals involved in the process ignited. Investigators said there were multiple possible sources of ignition. 

The investigation is ongoing. 

The contractor suffered serious injuries and remains hospitalized at the Johns Hopkins Bayview Burn Center.

Original post:

A man was seriously injured this afternoon inHouse explosion with fire, 4200 block Twin Circle Way, Lansdowne a house explosion and fire in Lansdowne.

The patient, reportedly 29 years old, was transported by ground to the Johns Hopkins Bayview Burn Center. He originally was classified a Priority 1 patient, but later was downgraded to Priority 2.

BCoFD crews were dispatched at 12:02 p.m. to a townhouse explosion with fire in the 4200 block of Twin Circle Way, 21227. Callers to 911 reported an odor of gas at the location and the sound of an explosion.

First-arriving crews reported heavy fire with the back wall in danger of collapse and, at 12:10 p.m, requested a working fire assignment. Crews knocked the fire at 12:22 p.m. The home suffered heavy damage. Three other units suffered less severe damage.

The patient reportedly was working at the home when the incident occurred. A family of four was at home at the time and self-evacuated.

An investigation will be conducted by Baltimore County Police fire investigators.