E PLURIBUS UNUM

NATIONAL TRA SPORTATION

B OARD

SAFE T Y

N

National Transportation Safety Board 

Washington, D.C. 20594 

Hazardous Materials Accident Brief

Accident No: DCA03MZ002 

Transportation Mode: Highway 

Location: Middletown, Ohio 

Date of Accident: August 22, 2003 

Time: 8:20 a.m. eastern daylight time 

Carrier: Amerigas Corporation 

Shipper: AK Steel Corporation 

Vehicle: MC-331 cargo tank 

Injuries: 5 people treated and released 

Property Damage: About $25,000 

Material Released: Anhydrous ammonia, a poisonous and corrosive gas 

Type of Accident: Cargo tank head fracture 

The Accident 

At 7:17 a.m., on August 22, 2003, 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, about 7:40 a.m., 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). 

About 8:20 a.m., 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. 

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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. 

Cargo Tank Information 

The accident cargo tank was a U.S. Department of Transportation (DOT) specification MC 

331 cargo tank. Its serial number was 59721, and it had been manufactured by Lubbock 

Manufacturing Company

1

 in 1977. The cargo tank was made of ASTM A517 quenched and 

tempered steel.2

 ìQTî was stenciled to the right of the cargo tankís specification plate to show that 

the tank was made of quenched and tempered steel. (See figure 1.) As manufactured, the nominal 

thickness of the shell was 0.399 inch, and the minimum thickness of the heads was 0.250 inch. Each 

of the two heads was a welded assembly of eight pieces of formed steel: a center round portion 

surrounded by seven separate radial pieces that were welded to the tank shell. (See figure 2.) The 

water capacity of the tank was 10,600 gallons. It had a maximum allowable working pressure of 265 

psig at 150 degrees F. 

 1

 Lubbock Manufacturing Company, Lubbock, Texas, sold its assets to Evans Products, Inc., in December 1980. 

Cargo tanks were manufactured under the name Evans Tank Company until 1984, when the company ceased 

operations. 2 Quenching and tempering is a heat treatment intended to improve the characteristics of steel, including increasing 

the yield strength. Yield strength is the stress at which a material starts to permanently deform.

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Figure 1. Accident cargo tank with ìQTî by the vehicle specification plate.
Figure 2. Schematic drawings of front head showing the crack locations (ìaî arrow shows 

the location of the through-wall crack; arrows without labels show the locations of other 

cracks).

 

Midwest TankWorks, Inc., had done the last DOT-required tests3 on the cargo tank: a 

hydrostatic test and a magnetic particle inspection in March 2002 and a visual inspection in March 

2003. No exceptions had been noted. 

Postaccident Examination 

A postaccident examination revealed a 16-inch long through-wall crack next to the radial 

weld in the front head at the 1 oíclock 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 oíclock 

position (see figure 2). 

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 3

 Title 49 CFR section 180.407 requires MC 331 cargo tanks to be hydrostatically tested every 5 years and visually 

inspected annually. The section also requires that all MC 331 cargo tanks that are constructed of quenched and 

tempered steel and used to transport anhydrous ammonia be given a magnetic particle inspection just before and in

conjunction with the hydrostatic test.
Figure 3. Through-wall crack in tank head.

The through-wall crack was opened at the Safety Board materials laboratory. Cleaning the 

opened crack revealed a granular surface that had no indications of crack arrest marks. Scanning 

electron microscopic (SEM) examinations of typical sections removed from the crack surfaces 

showed that almost the entire surface topography was composed of corrosion damaged intergranular 

separation. 

The bending forces generated when the through-wall crack was opened also opened a 

previously undetected crack near one end of the through-wall crack. The undetected crack was about 

3 inches long. SEM examinations found the crack topography to be very similar to the surfaces of 

the through-wall crack, corroded intergranular separation. 

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Stress-Corrosion Cracking 

According to the American Society for Metalsí Metals Handbook, Desk Edition,4

intergranular fracture in carbon steel in the presence of a caustic material, such as anhydrous 

ammonia, is typical of stress-corrosion cracking. Stress-corrosion cracking occurs in a susceptible 

material when it is exposed to sustained tensile stresses and a specific environment. 

A paper by A. W. Loginow titled Stress-Corrosion Cracking of Steel in Liquefied Ammonia 

Service5

 said that in the 1950s, the Agricultural Ammonia Institute instructed a research committee 

to find out why a number of carbon steel tanks containing anhydrous ammonia had failed. The 

committee determined that the failures were most likely caused by stress-corrosion cracking and that 

the probability of cracking increased as the yield strength of the steel increased. Testing showed that 

the addition of at least 0.1 percent water by weight6

 to the anhydrous ammonia inhibits stresscorrosion cracking in carbon steel. The committee recommended, in part, that ammonia contain at 

least 0.2 percent water to inhibit cracking. 

Mr. Loginow also said that stress-corrosion cracking began to occur in DOT specification 

cargo tanks in the mid-1960s because improvements in production technology had increased the 

purity of the ammonia by reducing the water content. During that period, a DOT-initiated 

examination of cargo tanks constructed from ASTM A517 quenched and tempered steel revealed a 

strong relationship between anhydrous ammonia that contains less than 0.2 percent water and the 

increased incidence of stress-corrosion cracking in cargo tanks. As a result, in 1975, the DOT 

adopted regulations under which cargo tanks made of quenched and tempered steel could be used for 

anhydrous ammonia only if the solution contained at least 0.2 percent water. 

The Hazardous Materials Regulations (Title 49 Code of Federal Regulations, Parts 171-180) 

require that anhydrous ammonia transported by highway be in either DOT specification MC-330 or 

MC-331 cargo tanks. Section 173.315(a), note 14, provides that such a cargo tank is authorized for 

all grades of anhydrous ammonia if the tank is not constructed of quenched and tempered steel 

(NQT). If the cargo tank is constructed of quenched and tempered (QT) steel, as the accident tank 

was, it is authorized only for anhydrous ammonia having a minimum water content of 0.2 percent. 

Each cargo tank must be marked near the specification plate with the letters ìNQTî or ìQT,î as 

applicable.7 The shipping papers for anhydrous ammonia transported by highway in a cargo tank 

must be marked, as applicable, with either ìNOT FOR Q and T TANKSî or ì0.2 PERCENT 

WATER.î8

 4

 Boyer, Howard E. & Gall, Timothy L., Metals Handbook, Desk Edition, American Society for Metals, Metals 

Park, Ohio, 1985, Section 32-24. 5

 Loginow, A.W., Stress-Corrosion Cracking of Steel in Liquefied Ammonia Service, National Board of Boiler and

Pressure Vessel Inspector ìBulletin,î Volume 45, No. 6, October 1988. 6 All percentages of water in anhydrous ammonia that are referred to in this paper are calculated by weight. 7

 Title 49 CFR section 172.328(c).

8

 Title 49 CFR section 172.203(h).

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Hazardous Materials Information 

 Anhydrous ammonia is a poisonous and corrosive gas. According to the Center for Disease 

Control and Preventionís National Institute for Occupational Safety and Health (NIOSH), the low 

lethal concentration (LCLO)

9

 of anhydrous ammonia for humans is 5,000 parts per million (ppm) for 

a period of 5 minutes. NIOSH also stipulates that the IDLH10 (immediately dangerous to life or 

health) of anhydrous ammonia is 300 ppm. Humans can detect the odor of anhydrous ammonia at 3 

to 5 ppm. 

Under DOT regulations (49 CFR Parts 171-180), anhydrous ammonia is classified and 

regulated for domestic shipments as a nonflammable gas. Pressure vessels, including cargo tanks, 

containing anhydrous ammonia must be marked ìInhalation Hazard.î Also the shipping papers for 

those packages must contain the words ìInhalation Hazardî in association with the shipping 

description. 

Anhydrous ammonia is transported as a liquefied compressed gas in pressure vessels (tank 

cars, cargo tanks, and cylinders). If it is released from the pressure vessel, anhydrous ammonia will 

immediately return to a gaseous state and expand rapidly.

Anhydrous ammonia is a byproduct of the process of converting coal into coke, which is 

used as a fuel in blast furnaces to produce steel. 

Shipper Information 

AK Steel is a steel production facility in Middletown, Ohio. AK Steel produces its own coke 

and stores the resulting anhydrous ammonia in stationary tanks. 

AK Steel sells about six cargo tank loads of anhydrous ammonia a month to Univar USA, 

Inc., (Univar) in Cincinnati, Ohio. According to AK Steelís records, the accident cargo tank was the 

only one in which AK Steelís anhydrous ammonia had been transported in the past year.11

AK Steelís laboratory shift manager analyzes each cargo tank load of anhydrous ammonia 

for moisture. He stated that the anhydrous ammonia almost always contains less than 0.2 percent 

water. AK Steelís records show that the anhydrous ammonia loaded in the accident cargo tank 

during the 4 months preceding the accident typically contained less than 0.1 percent water. 

 9

 The lowest concentration of a substance that has been reported to have caused death in humans. 10 NIOSH, in its ìRespirator Decision Logic,î defines IDLH exposure condition as a condition that poses a threat of 

exposure to airborne contaminants when that exposure is likely to cause death or immediate or delayed permanent

adverse health effects or prevent escape from such an environment. 11 According to the carrierís records, the same cargo tank had also carried loads of anhydrous ammonia from

Royster Clark in Finney, Ohio. The shipping papers and records provided by Royster Clark indicate that each load 

in the cargo tank contained at least 0.2 percent water.

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AK Steel generates the shipping papers for the cargo tanks loaded at the Middletown plant. 

The shipping papers for the 12 months before the accident did not include the words ìNOT FOR Q 

and T TANKS.î 

AK Steelís quality standard operating practice #01-0141-02 for loading trucks and tank cars 

with anhydrous ammonia in use at the time of the accident did not require loaders to verify before 

loading that the receiving cargo tank was appropriate for anhydrous ammonia that was less than 0.2 

percent water. The practice did not tell the loader what to do if the cargo tank was marked ìQT.î 

On September 11, 2003, AK Steel revised the quality standard operating practice, which 

now says: 

Before loading check specification plate located on side of tanker, must be labeled 

NQT. If labeled QT, or has no label, DO NOT LOAD. Contact Shift Manager. 

All AK Steel employees involved in loading anhydrous ammonia into cargo tanks are presently 

being trained in the revised quality standard operating practice. 

Additionally, AK Steelís shipping papers for anhydrous ammonia now contain the words 

ìNOT FOR Q and T TANKS.î 

Carrier Information 

The cargo tank semitrailer involved in the accident was operated by Propane Transport 

International (PTI),12 the Houston-based division of Amerigas.13 PTI handles the semitrailer delivery 

service of liquefied petroleum gas (LPG) to the Amerigas distribution sites. PTI also transports 

semitrailer loads of LPG and anhydrous ammonia for other customers, such as Univar, which had 

hired PTI to haul anhydrous ammonia from AK Steel. PTI is the only division of Amerigas that 

transports anhydrous ammonia. About 1 percent of PTIís business involves transporting anhydrous 

ammonia. PTI employs 121 company drivers and 145 owner-operator drivers. (The driver involved 

in the accident was an owner-operator of his own tractor.) PTI has 331 cargo tanks used to transport 

LPG (23 of which have also been used to transport anhydrous ammonia) and 7 cargo tanks used 

exclusively for anhydrous ammonia. The cargo tank involved in the accident was used only for 

anhydrous ammonia. 

PTI uses the safety information about transporting LPG and the hazardous material training 

examination for drivers that are developed by the Amerigas corporate safety office. PTI has added 

items to its driverís training examination that are relevant to operating cargo tank semitrailers. 

Before the accident, neither Amerigas nor PTI had added questions about anhydrous ammonia to the 

examination. 

 12 PTI was a wholly-owned subsidiary of Amerigas until 1995, when it became an operating division. 13 The headquarters of Amerigas are in Valley Forge, Pennsylvania.

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PTI safety staff did not check shipping papers regularly to see whether they had the DOTrequired information. The PTI manager of safety and accounting said that about 99 percent of PTIís 

business is LPG and that, except for quantity, the DOT-required information on LPG shipping 

papers does not vary and does not require close monitoring. 

PTIís driverís handbook has information about anhydrous ammonia and the required water 

content. The 1995 version of the handbook said: 

A small amount of water (.002%) [Sic] is added for transportation in transport 

trailers constructed of T1 steel. [14]

The same paragraph was still in the handbook in 1998 but no subsequent versions of the 

handbook were located by PTI until the current handbook. PTI management gave the Safety Board a 

page from a current driverís manual that was dated September 2003 and said: 

A small amount of water (0.2%) is added for transportation in cargo tank trailers 

constructed of QT (quenched and tempered) steel. This quantity must be marked on 

the bill of lading. If the anhydrous ammonia contains less than 0.2%, it can only be 

hauled in a NQT (not quenched and tempered) steel cargo tank. 

At meetings between October and December 2003, PTIís regional logistic managers gave 

drivers copies of the current page about anhydrous ammonia. At the meetings, the managers stressed 

that drivers should check the shipping papers for the required information before loading anhydrous 

ammonia. Similar training about anhydrous ammonia will be given by driver trainers as they review 

the manuals with the new drivers. 

The driver of the accident cargo tank took PTIís initial training when he was hired in 1994, 

and records indicate that in 1995 he received a 1995 driverís handbook; no receipt records for other 

versions were discovered. After the accident, he said that he had not been told about the requirement 

that shipping papers for anhydrous ammonia specify the water percentage. He also said that before 

the accident, he had not known that the anhydrous ammonia carried in his cargo tank should contain 

a certain amount of water and that it is dangerous to transport anhydrous ammonia that is less than 

0.2 percent water in cargo tanks that are made of quenched and tempered steel. On October 21, 

2003, he attended the meeting where the regional logistic managers discussed the current page about 

anhydrous ammonia. 

 14 T-1Æ steel is a U.S. Steel Corporation trademark for quenched and tempered steel used in pressure vessels and is

comparable to ASTM A517.

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Probable Cause

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 Corporationís 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. 

Adopted: July 22, 2004 

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