Ammonium Nitrate Dangers Told in Newly-Found Report
The author is indebted to officers of the Long Beach and Los Angeles Fire Departments for their cooperation in preparing this report. Chiefs Frank S. Sandeman and Leonard Foster of Long Beach, Chief John Alderson of Los Angeles and Inspector Don Wilson, also of the Los Angeles Department, were especially helpful. Much of the research for this report was done by Capt. Leonard E. Farrar of the Long Beach Bureau of Fire Prevention, and photo credits go to Capt. Farrar and Capt. Claude A. Conlin, Jr., of the Los Angeles Fire Department for this report of exceptional historical significance.
FIRE chiefs and firemen in industrial centers, especially those whose departments have a waterfront area to protect, are keenly aware of the dangers of handling ammonium nitrate. The now historic disaster in Texas City, Tex., on April 16 and 17, 1947, will always remain a symbol of “it can happen here.”
At the time of the Texas City disaster, explosion experts compared it to a similar one in Oppau, Germany, on Sept. 21, 1921, when a concrete silo containing 4500 tons of the chemical exploded. The detonation of this enormous pile of ammonium sulfonitrate (ammonium nitrate-ammonium sulfate) fertilizer salt killed 450 persons, leveled more than 700 homes and caused most of the buildings housing the plant to practically disappear.
Although there were many similarities between the Texas City disaster and the one at the I.G. Farban Industries plant in Oppau, authorities have never found a complete explanation of what caused the German disaster.
Recently, officers of the Long Beach Fire Department came across a retired German chemist who shed light on this mystery. He was thoroughly questioned and the subsequent report was placed in the archives of the Los Angeles Fire Department, where it was made available to FIRE ENGINEERING and its readers.
Although the Oppau disaster occurred more than 30 years ago, this report is believed to be the first time that substantial evidence has been uncovered as to the exact cause of this disaster. FIRE ENGINEERING therefore offers it to its readers in the belief that the discovery of the Long Beach and Los Angeles Fire Departments of this significant material should be made available to the fire service as a whole.
First, however, some backgrounding is necessary.
The Farban plant manufactured synthetic dyes, pharmaceuticals and related products and employed about 30,000 people. The plant operated under the Haber process, which employed a direct reaction between atmospheric nitrogen and hydrogen to form ammonia. The synthesis is carried out under extremely high pressures and temperatures. The pressures applied ranged from 3000 to 3500 pounds per square inch at temperatures of 400 degrees centigrade. This Haber process is only successful if a suitable iron catalyst is employed and if all gases entering the reaction are carefully purified. Under such conditions a portion of the hydrogen-nitrogen mixture is converted into ammonia.
The ammonia so formed leaves the reaction chamber together with the unconverted gases and they pass through high pressure water scrubbers whereby the ammonia dissolves in the water while the residual unconverted gases are returned through a booster pump to re-enter the reaction chamber. Another means of removing the ammonia is by subjecting the exit gases from the high pressure reaction chamber to refrigeration, whereby the ammonia liquefies while the residual gases are recirculated.
A large part of the Farban plant served the printary purpose of ammonia synthesis. Under this, the hydrogen was made in an enormous gas plant by means of the water gas reaction. The nitrogen was obtained by air liquefaction, thereby separating oxygen from the nitrogen as a by-product. Extremely elaborate gas purification systems were involved and occupied a substantial area of the plant.
The purification had to be almost perfect so as not to poison the catalyst in the reaction chamber. For example, from the hydrogen the last traces of carbon monoxide had to be removed to prevent the formation of iron-pentar-carbonyl with the contact-mass.
Ammonia, the primary step in nitrogen fixation, was now available for the following purposes: The production of
nitric acid by means of the Ostwald process which might either be used for production of nitrogen compounds such as fertilizers and/or for the nitration of organic substances such as toluene or phenol for explosives.
The primary purpose of the plant during peacetime was the manufacture of nitrogen fertilizers. Ammonium sulphate, ammonium nitrate and as a later development, a new type of fertilizer known as a double salt of the both was marketed under the name of ammonium sulphate-nitrate. The reason for producing this product was that it carried a higher nitrogen content than the sulphate. Ammonium nitrate, as such, was not manufactured in substantial quantities because of its possible explosive violence.
Contrary to the processes used in the United States for making ammonium sulphate: blowing ammonia into sulphuric acid to produce the salt, the Germans used an indirect method, resorting to the use of finely ground gypsum and agitating this suspended mixture with ammonia to form calcium hydroxide, a waste product, and ammonium sulphate as the end product.
In making the double salt, one difficulty was encountered. The finished material absorbed water during storage and consequently became lumpy. Since the demand for this fertilizer was seasonal rather than continuous, enormous quantities had to be stored in large silos for months at a time. When the time for shipments arrived, means had to be found to break up the salt into smaller lumps to be carried by belt conveyors into a crushing mill. From there the salt passed through a dryer and finally was loaded by chutes into box cars.
It was a rather difficult operation to break up the enormous mass of salt cake in the silo and the only convenient means of doing this was by drilling holes into the salt and planting sticks of dynamite all around the base of the salt pile.
A 60-man “crew carried out this work under leadership of a foreman for many years. There had been no previous accidents. It was considered absolutely safe to so handle this product since elaborate preliminary tests under the most adverse conditions showed that the salt could not be exploded itself. All precautions to avoid accidents were taken and the explosive storage was far outside the premises of the plant and well-protected against lightning and saboteurs. Only the amount of explosives used daily was brought into the plant.
Everybody thought it couldn’t happen here. But it did happen on Sept. 21, 1921, at 7:31 a.m. Here’s the story that probably has never been told before:
The chain of circumstances leading up to one of the most powerful blasts of the pre-atomic age started when the explosive engineer who usually supervised all blastings to loosen the packed chemical was called away from the plant. He had been sent to a subsidiary plant in a nearby city to knock down a large chimney. The foreman left in charge had his own idea on how to modify the timetested method. A surviving witness who spoke to this foreman 10 minutes before the explosion reported later that the foreman believed his own method would be 25 times as effective as the prevailing one. The foreman, moreover, did not obtain permission from his superior to try it out.
The foreman used large quantities of the most sensitive fulminate of mercury in place of the nitroglycerine charge which was usually employed. Since the powder house was located far outside the plant premises, it was left intact by the explosion. A check substantiated the idea that a radical change in the amount and type of explosives used on that day occurred. Unbelievable as it might appear, the foreman actually succeeded in loading the fulminate of mercury without an accident. It was known to the management and the explosive engineer that a sufficiently high shock wave such as may result from detonations of either mercury or silver fulminate could under certain conditions explode the salt itself.
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The 70-man crew placed the deadly charge and then according to usual procedure climbed on top of this small mountain of salt cake until the foreman detonated the explosive by means of a conventional electrical impulse generator. The 70 men and the foreman scampered to the top of the salt cake in this long dry-dock sized silo until the explosion came! Obviously, they were blown to bits.
The silo, which was completely destroyed, left a cone-shaped crater 175 yards wide at its longest diameter and 40 yards deep. One day later, the crater filled with water to the same level as the nearby Rhine River.
Other sections of the sprawling chemical plant were badly damaged. The blast swept steel frame buildings entirely clear of brick, cement and glass and twisted the gigantic girders into grotesque shapes. Rubble was nearly 20 feet deep from the demolished buildings. Gigantic bridges which carried pipelines between the various buildings were demolished by huge slabs of concrete and other debris which shot throughout the area.
The force of the explosion was felt as far distant as Frankfurt, some 60 miles from Oppau. The town of Oppau itself was almost completely destroyed. While some houses remained standing, they were all so badly damaged that they had to be torn down and rebuilt. Casualties were high in this city, of 25,000 people and probably 2,500 of them suffered serious injuries and many more were injured less critically. Other nearby towns were also damaged. The twin cities of Ludwigshafen-Mannheim reported that the greater portions of windows and show cases were shattered, shingles were stripped off rooftops and trees shorn of their leaves from the shock wave.
Some 300 yards from the crater were a number of gas bolder sections. The largest of them held approximately 50,000 cubic yards of hydrogen gas. This tank exploded in one instantaneous flash, throwing its bell 300 feet and crumpling it like a newspaper.
Nearby was a huge Ostwald ammonia oxidation building which held large storage tanks for fuming nitric acid. All tanks were punctured by flying debris and the nitric acid spilled out, drenching the area. The acid slowly seeped into a basement of the building where 100 workmen were trapped by fallen debris. An attempt was immediately begun to free them before the acid reached their area. The 100, however, died a slow death and during the rescue atttempts, three volunteers also were fatally burned. All further rescue attempts were then given up and the agonized screams of the trapped slowly dwindled into silence.
In the same general area was a 200foot high boiler used as part of a steam generating plant. It was hit by flying debris and exploded with a deafening roar. No trace of the boiler was found.
Capt. Farrar’s source for the report was the late E. A. Boesing, a chemist at the plant, who miraculously escaped injury. Boesing was thrown underneath a crane which buckled. The gigantic steel contraption twisted and when it landed on him formed a perfect shelter. The building he was in was nearly completely destroyed, yet the warped crane shielded him from flying glass, debris and the collapse of a 12-inch thick concrete roof. When the dust settled. Boesing found a layer of dust and rubble 15 inches deep.
The total damage ran into tens of millions of dollars, which was a considerable figure compared to today’s inflated prices.
Ironically, a silo nearby the one that was detonated did not explode. It contained 10,000 tons of the chemical. Contrary to conventional silo structure, these enormous storage warehouses were not of the cylindrical upright type but were very large structures built of reinforced concrete and were almost identical in appearance to drydocks. The charge was stuffed into these silos after the crew drilled a number of holes directly into the caked salt.
While everyone in the plant had always been afraid of the high pressure division (where reactions were carried on under pressures of 3500 pounds per square inch at approximately 1000 degrees Fahrenheit), the remarkable fact remains that not a single piece of this monstrous apparatus exploded during the series of blasts, except such portions of the equipment that were directly hit by flying debris, such as steel, beams, concrete blocks and the like up to 20 tons and more.
Reconstruction of the plant at first looked hopeless. The debris was cleared, however, and six weeks later the first two high pressure units went back into operation Everything had been completely rebuilt eight months later. It’s interesting to note that the Farban Co. plant at Ludwigshafen was damaged by an explosion on July 28, 1948, killing 184 persons and injuring 2500 others.