1951 — Feb 8, LPG vapor explosion, Minnesota Mining & Manufacturing, St. Paul, MN–14

–14 Earle. “The 3-M Explosion.” Quarterly of National Fire Protec. Assoc., 44/4, Apr 1951, p. 305.
–14 Mannan. Lee’s Loss Prevention in the Process Industries (Vol. 1, 3rd Ed.), 2005, 17-289.
–14 NFPA. “Fires Causing Large Loss of Life.” Handbook of Fire Protection. 1954, p. 36.

Narrative Information

Earle: “At 8:21 on the morning of February 8, 1951, a violent explosion of liquefied petroleum gas vapors in the basement seriously damaged a reinforced concrete building and brought death to 14 employees of the Minnesota Mining & Manufacturing Company in St. Paul, Minns. The property and production loss was estimated at over $1,000,000.

“The minerals building in which the explosion took place was approximately 85 ft. by 90 ft. with brick walls and windows set in steel sash (not arranged for explosion venting)…The floors and roof were of heavy reinforced concrete with enclosed floor openings which undoubtedly helped to confine the major damage to the lower floors….

“The minerals building was used for processing con-combustible materials used in the preparation of abrasive products. Heat treating and burning furnaces located on the 4th and 5th floors used butane gas as fuel….

“Liquid butane was usually received by tank car and transferred to the storage tank by a pump. All butane unloading was done by authorized plant personnel.

“Due to transportation difficulties occasioned by the existing railroad strike it was necessary to have liquefied petroleum gas delivered by tank truck and a temporary unloading connection was installed on the butane storage tank to accommodate the tank truck. In addition to the usual fill, vent and discharge connections the vapor space of this butane storage tank was connected to a low pressure air supply line…so that the butane tank could be pressurized by air in very cold weather for the purpose of transferring liquid butane from the storage tank to the vaporizer. This air supply line was connected to the shop air system and ran underground from the basement of the minerals building to the butane storage tank. A water condensate leg with a drain valve was connected to the air supply line in the basement of the minerals building.

“Just before the explosion a tank truck containing liquefied petroleum gas (stated to be 70% propane and 30% butane instead of the usual 100% butane) containing odorant was connected to the temporary filling connection at the storage tank and the transfer of the fuel was started. The temporary filling connection was arranged so that liquefied petroleum gas could be pumped from the tank truck into the low pressure air supply line at a point close to the butane storage tank. It was intended that the liquid fuel would pass through a short section of the air supply line and into the storage tank.

“Shortly after the unloading operations began and several minutes prior to the explosion an employee reported a serious leak of gas in the basement to a foreman in the minerals building. A man was immediately dispatched to notify the Safety Engineering Department and then to get assistance from the maintenance shop according to the outlined procedure. This man notified the Safety Department and was told to go at once to the near-by maintenance shop, which he did. He met the steamfitter foreman, who, on learning the situation, started on the run for the minerals building. Before he reached it the explosion took place and he at once ran to the vaporizer unit and shot off the gas from the entire system. He then rushed to the butane storage tank and made sure the butane discharge valve was closed.

“When the explosion occurred the unloading of liquefied petroleum gas from the tank truck was discontinued immediately.

“All employees in the lower floors of the minerals building were killed and what progress they had made to eliminate ignition sources, etc., in the interim between the discovery of the gas leak and the explosion is not known.

“The first and second floors with the equipment stored thereon and in the basement were completely destroyed….

“How It Happened

“A study of the arrangement of the temporary fillings connection on the air supply line at the butane storage tank revealed that it was possible during the unloading operation for liquefied petroleum gas to flow back into the underground air supply line. With an open drain valve on the water condensate leg gas could thus enter the basement of the minerals building. It was concluded that liquefied petroleum gas entered the basement of the mineral building by means of this air supply line and condensate leg and was ignited y one of several ignition sources which existed in the basement….

“The outstanding lesson of this explosion is the danger of connecting a shop air system to a liquefied gas system in such a way that the gas can enter the building….

“It is understood the Minnesota Mining and Manufacturing Company has abandoned the use of liquefied petroleum gas in this plant and will use natural gas in the future.” (Earle, Stanley. “The 3-M Explosion. Quarterly of the National Fire Protection Association, Vol. 44, No. 4, Apr 1951, pp 305-308.)

Mannan: “Incidents of vapour escapes into, and explosions in, buildings (VEEBs) are exemplified by those at St Paul in 1951 and Attleboro in 1964…In the first an escape of LPG at a loading terminal caused an explosion which killed 14 people.” (Mannan. Lee’s Loss Prevention in the Process Industries (Vol. 1, 3rd Ed.), 2005, p. 17-289.)

National Fire Protection Association: Gas Explosion, Minnesota Mining & Manufacturing Co. Abrasives Factory. (NFPA. 1954, p. 36.)

Sources

Earle, Stanley. “The 3-M Explosion. Quarterly of the National Fire Protection Association, Vol. 44, No. 4, Apr 1951, pp 305-308.

Mannan, Sam (Ed.). Lee’s Loss Prevention in the Process Industries: Hazard Identification, Assessment and Control (3rd Ed., 3 Vols.). Burlington, MA: Elsevier Butterworth-Heinemann, 2005.

National Fire Protection Association. “Fires Causing Large Loss of Life.” Handbook of Fire Protection (11th Ed.). Boston, MA: NFPA, 1954, pp. 33-36.