Last week was the anniversary of the anhydrous ammonia truck accident in Houston back in 1976 and out of that incident came what we call “Shelter-in-Place”. About 11:08 a.m., on 11 May 1976, a Transport Company of Texas MC 331 tractor-semi trailer transporting 7,509 gallons of anhydrous ammonia struck and penetrated a bridge rail on a ramp connecting I-610 with the Southwest Freeway (U.S. 59) in Houston, Texas. The tractor and trailer left the ramp, struck a support column of an overpass, and fell onto the Southwest Freeway, approximately 15 feet below. The anhydrous ammonia was near instantaneously released from the damaged tank semi trailer. Six persons died as a result of the accident, 78 persons were hospitalized, and approximately 100 other persons were treated for injuries.