by Tom Jenson
Fire Code Specialist

Have you ever wondered why mercaptan — the chemical that smell of “rotten eggs" — is routinely added to natural gas? Did gas companies do it because alerting people to a gas leak in the building was simply the right thing to do? As with so many requirements in fire and building codes, the introduction of mercaptan into natural gas resulted from a tragedy.

As I've written in previously newsletters about panic hardware, out-swinging doors and flammable interior finishes, it took the deaths of 294 students and teachers in a natural gas explosion for laws to be enacted requiring an odorant be added to natural gas.

At 3:17 p.m. on March 18, 1937, a manual training instructor turned on an electric sander. The spark from the switch is believed to have ignited the gas-air mixture. The resulting explosion pushed out walls and lifted the roof off the building before crashing back down. The main wing of the structure collapsed.​

The loss of life could have been much greater, but first- through fourth-grade students had been dismissed early. An estimated 500 students and teachers were in the building when the explosion occurred minutes before the end of the school day. Many of the victims were only identifiable by clothing or personal items.

To save money, the school board canceled their natural gas contractor and had plumbers install a tap into a gasoline company's residue natural gas line. The connection to the residue gas line was later determined to be faulty, and that allowed the odorless gas to leak into the school undetected. Students had complained of headaches for some time, but not much attention was given to this.

The Texas legislature took immediate action and passed legislation requiring odorant to be added to natural gas to make it easier and faster to detect leaks. Other states took similar action to prevent future disasters. 

Read more about this explosion fire at Wikipedia or American Oil and Gas Historical Society. Or take a look at the vintage ​newsreel report of that tragedy.

Trivia: New United Press International reporter Walter Cronkite, on one of his first assignments, stated (decades later) “I did nothing in my studies nor in my life to prepare me for a story of the magnitude of that New London tragedy, nor has any story since that awful day equaled it." And this reporter covered World War II and the Nuremberg trials.

You can reach our fire code team at fire.code@state.mn.us.​​