Ohio Cargo Tank Release of hazardous Materials

Middletown, Ohio: An Amerigas Corporation (Amerigas) cargo tank semitrailer arrived at the AK Steel Corporation (AK Steel) facility in Middletown, Ohio. The driver pulled the vehicle up to the fill location and helped an AK Steel employee hook up to the fittings for a plant storage tank. According to the driver, the AK Steel employee began transferring anhydrous ammonia, a poisonous and corrosive gas, from the storage tank to the cargo tank. The driver said that it took about 30 minutes to equalize the pressure between the storage tank and the cargo tank. He said that once the pressure was equalized, the internal pressure in the cargo tank was 130 pounds per square inch gauge (psig).

While the cargo tank was still being loaded, its front head cracked open, releasing vapor. The driver, who had been resting in the tractor, got out and saw the escaping vapor. He said that he activated the emergency shut off device for the cargo tank and that according to the gauges, the cargo tank was a little less than half full, the internal pressure was about 170 psig, and the temperature of the anhydrous ammonia was 80 degrees F.

About 100 employees and contract workers were evacuated from the buildings downwind of the cargo tank and moved to safer locations. Five people were treated for inhalation injuries and released. The cost of repairing and replacing damaged equipment was about $25,000.

A postaccident examination revealed a 16-inch long through-wall crack next to the radial weld in the front head at the 1 o'clock position. (See figure 3.) An internal inspection and magnetic particle inspection also revealed two additional cracks that did not penetrate through the metal: one closer to the center portion of the head on the same radial weld as the through-wall crack, and the other on the weld between the center portion of the head and the radial piece at the 3-to-4 o'clock position.

The National Transportation Safety Board determines that the probable cause of this accident was the failure of AK Steel Corporation to establish and implement loading procedures that would prohibit using a cargo tank manufactured of quenched and tempered steel to transport anhydrous ammonia containing less than 0.2 percent water by weight, resulting in stress-corrosion cracking and tank failure. Contributing to the cause of the accident was Amerigas Corporation's failure to tell its drivers that anhydrous ammonia containing less than 0.2 percent water by weight should not be loaded into cargo tanks manufactured of quenched and tempered steel.