Firefighters comb the debris after an explosion tore apart a machining plant in northwest Houston Friday morning. - Screencapture Via KHOU

Firefighters comb the debris after an explosion tore apart a machining plant in northwest Houston Friday morning.

Screencapture Via KHOU

Two fatalities have been confirmed in an explosion that leveled much of a machining and manufacturing plant in northwest Houston Friday morning. The blast caused extensive damage to the surrounding neighborhood.

Operations on site are transitioning from an active hazard phase to a search and recovery phase, Houston Fire Chief Sam Pena said. Federal agencies such as the Chemical Safety Board and local authorities are conducting a joint investigation into the cause and origin of the blast.

"There is no indication of terrorism or anything intentional," Houston Police Chief Art Acevedo said.

At a 1 p.m. press conference Houston Fire Chief Art Acevedo said the probability is high that the two fatalities were employees working their shift at Watson Grinding in the 4500 block of Gessner. All other Watson employees have been accounted for except for two whose vehicles were found parked at the scene.

At least one person driving past the plant at the time of the explosion suffered injuries requiring transport to a hospital, Pena said.

"The guy was very close," Pena said. "His truck went flying."

Another 18 people visited area hospitals with injuries attributed to the blast and its concussion, Pena said.  

A hazardous materials team have secured valves to halt the release of gaseous chemicals into the atmosphere.  Pena identified one chemicals leaking from the site earlier as polypropylene, a plastic commonly used in packaging.

A 2,000-gallon polypropylene storage tank that was last filled Monday has been safely shut down. No other storage tanks on the site are leaking, Pena said. A full inventory of the chemicals on site is being conducted.

Air monitoring has not detected dangerous levels of toxic material near the scene, Pena said.

Firefighters had earlier chosen to let a small amount of fire remaining burn itself out rather than risk contaminated runoff from fire water, he said.

The blast, reported at about 4:30 a.m., broke windows and smashed doors throughout the surrounding area. Of the 199 homes in the West Branch and Carverdale neighborhoods surrounding the plant, 190 have been accessed by city officials as to continued inhabitability, Pena said.

"A lot of these homes with not be livable for several weeks," he said. "The closer to the blast the worse the damage. We have homes that have been shifted off their foundations."

Acevedo said that the affected area will be patrolled by police "24/7" to deter possible looting. Police are in the process of lifting the cordon around the area to allow residents who fled the chance to recover important possessions.

"We want to give them the chance to board up their homes," Acevedo said.

Pena reported this morning that the debris field from the blast extends across a quater-mile radius of the plant. That radius has since widen to nearly two miles. Acevedo asked that citizens finding evidence from the blast report its location to police without moving it.

A resident captured the explosion on a video doorbell and posted a clip to YouTube (watch above) showing a fireball rising in the distance from a front porch. Within a split second, the security camera was knocked over by the concussion.

At least two nearby schools will remain closed today, the CyFair school district reports. Students at other schools in the district will be kept indoors throughout the day.

Acevedo took advantage of the afternoon press conference to make a personal appeal to the U.S. Marine Corps with regard to a surviving family member.

"We have a 21-year-old Marine at Camp Lejeune in North Carolina," Acevedo said. "The Marine Corp will not release him to come home until it is fully confirmed that the fatality is who we say."

He asked the public to contact the military and let them know that "this Marine needs to be home with his family."