Local 2 has learned 121 facilities in Harris County have registered with the Environmental Protection Agency to use anhydrous ammonia.
Anhydrous ammonia is the same substance that exploded in West, Texas on Wednesday. But industrial health and safety experts have said fire and explosion is not the greatest risk from the substance.
According to the Centers for Disease Control, anhydrous ammonia is a colorless gas with pungent, suffocating fumes, and is used as an agricultural fertilizer and industrial refrigerant.
"If you go to a safety person and ask them what is your concern about anhydrous ammonia, flammability and explosiveness would not be high on my list. The health effects from the burns and injuries would be high on my list," said Dr. Robert Emery, Safety, Health, and Risk Manager with the University of Texas Public Health in Houston.
In 1976, less than a mile from the Houston Galleria, an overturned tanker truck carrying anhydrous ammonia overturned. The resulting casualties were not from fire but from a toxic cloud that escaped from the tanker.
"I started gagging, coughing, I couldn't breath," a commuter said on air May 11, 1976.
Seven people died and 178 people were injured died as a result of the disaster on I-610 at 59.
Today, hazardous loads are not allowed inside Houston's loop without special permit.
But there are tens of thousands of Harris County residents who live within two miles of plants using and storing anhydrous ammonia.
"Ain't nothing you can do it about it anyway, why worry about it," Pasadena resident, Clevonia Smith, said.