KTRH affiliate KPRC 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.

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"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.