Update on West: Causes and Consequences

Last Thursday, May 16, officials from the Fire Marshal’s Office of Texas and the federal Bureau of Alcohol, Tobacco, Firearms, and Explosives announced that the cause of the April 17 fertilizer-plant explosion in the town of West was “undetermined.”  However, they had eliminated a number of possible causes and narrowed the probable ones to three:  something to do with the 120-V electrical system in the plant, a golf cart stored in the same room with the ammonium nitrate bins, and arson. 

Considering the horrible jumble of wreckage that the explosion left behind, even this much progress in the investigation is laudable.  The investigators did determine that about 28 to 34 tons of ammonium nitrate, a fertilizer ingredient, exploded in the blast that dug a crater ten feet deep and 93 feet wide and caused seismometers to register the equivalent of a 2.1-magnitude earthquake.  It could have been worse:  another 140 tons of the material stored either onsite or in railcars at a nearby siding did not explode. 

The investigation revealed that the ammonium nitrate that exploded was stored in wooden bins next to bins of flammable seeds.  No sprinkler system was in place, and under current fire-code regulations none was required in the industrial facility. 

The reconstructed sequence of events is fairly brief.  At 7:29 PM on the evening of April 17, a fire was reported at the facility.  Unless there were personnel on site that late in the evening, it is likely that no one was present at the time and the first report was turned in only after smoke was visible outside the plant.  So the fire may have had some time to get going before it was reported.  This is significant, because when ammonium nitrate is heated, it can turn from a white powder into a solid mass that transmits shock waves well.

Nine minutes after the fire was reported, firefighters arrived and began to play water on the blaze, which the investigation stated did not contribute to the explosion.  Investigators speculated that as the fire progressed, a piece of heavy equipment might have come loose and fallen onto the now-solidified mass of ammonium nitrate, causing a detonation wave that led to two almost simultaneous explosions, 22 minutes after the fire was reported.  It was these explosions that killed fifteen people, most of them firefighters, and laid waste to 37 blocks of the small town. 

Not involved in the news conference at which these findings were announced, were members of the federal Chemical Safety Board (CSB), an agency charged with investigating chemical accidents with a view toward making recommendations about how to avoid them in the future.  A Dallas Morning News reporter interviewed members of the Board involved in the West investigation, and their work is still continuing.  Rather than focusing on the narrow question of exact causes, the CSB is examining the broader picture of how regulations affected the outcome of the incident and how community responses could have been improved.  Questions have been raised, for example, about the wisdom of storing so much explosive material literally across the street from an apartment complex, and not much farther from a school and a nursing home.  Any time a fire occurs at a facility where large amounts of ammonium nitrate are stored, prudence would dictate that at a minimum, the area within a possible explosion range should be evacuated. 

On July 30, 2009, a fire at a fertilizer plant in Bryan, Texas where large quantities of ammonium nitrate were stored led to the evacuation of thousands of residents of that college town (home to Texas A&M) as a precaution.  Fortunately, the fire burned itself out without incident and no damage outside the plant resulted.  But as the West explosion shows, things could have turned out very differently.  The Bryan incident also differs from West in that the people who accidentally started the fire were the ones who reported it promptly, giving more warning than otherwise.

While regulation is always a two-edged sword that can cause more harm than it alleviates, the West explosion will at least inspire re-examination of the whole complex of federal, state, and local laws, as well as insurance-company practices, that bear on the storage of ammonium-nitrate fertilizer.  Determining the appropriate level of regulation, as well as the appropriate agency or agencies to issue regulations, is not an easy task.  Local officials, especially in smaller towns such as West, rarely have the expertise to come up with customized, science-based regulations about hazardous materials that do not cause problems most of the time.  But federal regulations are a blunt instrument, and customarily matters such as fire codes are left to the states and local communities to decide on.  National organizations such as the National Fire Protection Association (NFPA) issue model guidelines and codes, but it is a state or local option as to whether these codes are made part of local laws. 

The deaths in the West explosion were preventable, and I for one hope that the memory of this tragedy will lodge in the minds of firefighters, code-enforcement officials, and governmental agencies who are in a position to keep such things from happening, or at least lower the chances of them happening, in the future.  The sharing of basic information and knowledge about how much of what stuff is stored where needs to be mandated so that first responders know both what they are dealing with and what is prudent to do in a given situation.  Firefighting is a hazardous job, and loss of life in the line of duty is one of the risks that firefighters take on when they join their companies.  But if better information and procedures, even if mandated by the federal government, will keep both firefighters and their communities safer in situations such as what happened in West last month, it may be time to change the way things are done.

Sources:  I referred to an article on the West investigation news conference published on the Dallas Morning News website on May 18 at http://www.dallasnews.com/news/west-explosion/headlines/20130518-in-west-investigators-focus-shifts-from-explosions-cause-to-closing-safety-gaps.ece.  I also used an article from the KRHD-TV website for information on the Bryan, Texas evacuation, found at http://www.abc40.com/story/10823244/ammonium-nitrate-fire-forces-mass-evacuation. 

The Disaster in West

Anyone who drives along Interstate 35 in Texas between Waco and Dallas or Fort Worth will pass through West, a small rural Texas town with a Czech heritage that was known, at least until last week, mainly for the pastries that you can buy at a bakery right next to the Interstate.  It would not have surprised me to learn that a distributor of fertilizers to local farmers operated on the east edge of town, nor that one of the kinds of fertilizer sold by the dealer was ammonium nitrate.  But when I learned of the tremendous explosion that killed at least 14 people, injured hundreds, and destroyed a good fraction of West’s built environment last Wednesday evening, April 17, my sadness was tinged with the knowledge that in warehousing large quantities of ammonium nitrate fertilizer, the firm was taking a chance that such a thing could happen.

Ammonium nitrate is a curious chemical.  A “molecule” consists of an ammonium ion (four hydrogens arranged around a nitrogen) with a positive charge and a nitrate ion (a nitrogen atom surrounded by three oxygen atoms) with a negative charge.  At room temperature, it is a solid, but its constituent elements are all gases.  And the only thing holding it together are the opposite charges retained by the ammonium and nitrate ions.  When heated gently in an open container, it breaks down into nitrous oxide (laughing gas) and water.  But when it is in contact with easily oxidized materials, such as the fertilizer urea or even some metals, heating can cause it to release oxygen, which greatly increases the heat of the reaction and can lead to a fire.  When confined by walls or even the pressure of a high stack of the material itself, burning ammonium nitrate can self-detonate.  A detonation is an explosive shock wave that travels at very high speed through a volume of material, and differs from burning as traveling by jet aircraft differs from walking.  This is apparently what happened a little after seven in the evening at the burning warehouse in West.

A back-of-the-envelope calculation of the power of the resulting blast can be done by beginning with an aerial view of the fertilizer plant before the explosion, which is still available on Google Maps.  Comparison with views of the devastated explosion site indicate that the explosion was probably centered in a large, flat warehouse building that appeared to be one story high and measured about 60 feet by 110 feet.  If we assume it was packed to a height of eight feet with ammonium nitrate (not an unreasonable assumption as distributors stock up for the summer growing season), the total mass of chemical in that building could have been as much as two thousand tons.  Pure ammonium nitrate has about a fourth of the energy content per pound as TNT.  Still, given these rough assumptions, if the whole mass went off at once, which it appears to have done, the force of the explosion could have been as great as a thousand tons of TNT, or one kiloton.

You may have run across the word “kiloton” in reference to nuclear explosions.  While there were fortunately no nuclear weapons or radioactive materials involved in the West explosion, the nuclear weapon dropped on Hiroshima at the end of World War II had a yield of only about 16 kilotons of TNT.  So what happened in West was one-sixteenth of a small nuclear bomb, in terms of destructive power.  No wonder it showed up on seismographs as a magnitude-2 earthquake.

If ammonium nitrate is so dangerous, why isn’t handling and use of it more regulated?  That’s a good question.  The Wikipedia article on ammonium nitrate notes that in 2005, Australia passed a Dangerous Goods Regulation law which requires a license for the sale or use of the material.  But if even licensed users store huge quantities of the stuff in places where it can catch fire and explode, licensing would not prevent disasters such as the one that happened to West last week, or Texas City in 1947, or over twenty other occasions since 1916 listed in a separate Wikipedia article devoted to ammonium nitrate disasters. 

Chemical companies that deal routinely with explosives know how to handle these materials so that when they explode, the explosions are limited to a small area that is sacrificed in order to protect the rest of the property and lives involved.  You simply restrict the amount of explosive allowed in one place to a maximum amount that you can afford to blow up, and then physically isolate it from all other concentrations of explosive in a series of small bunkers.  If the fertilizer stored in the West Fertilizer Company plant had been dispersed in this way, perhaps one of the small storage areas might have blown up, but with sufficient earth-berm isolation and other precautions, the explosion would not have spread.

That is small comfort for the survivors in West.  And as a practical matter, you can handle ammonium nitrate in an ordinary way without special precautions, as it is done thousands of times each year around the world, and most of the time, nothing bad will happen.  If the West firm had been required to invest in the additional storage facilities needed to treat ammonium nitrate as a true explosive, it would have gone out of business for sure.  (News reports indicate the firm nearly went bankrupt a few years ago and was rescued at the last minute by the present owner.)  So we face the dilemma of either requiring a huge investment in safety facilities on the part of fertilizer manufacturers and retailers everywhere to prevent disasters like West, or we leave things as they are and wait for the next one.

A compromise solution might be the rigorous training of anyone who deals with ammonium nitrate, enforced by a licensing law similar to the one on Australia.  This would include mandatory evacuations based on scientific calculations of a worst-case explosion whenever a fire occurs near large quantities of the stuff.  While regulations like this would not have prevented the damage caused by the West detonation, it could have reduced the death toll. 

Our thoughts and prayers are with the residents of West, whose tragic experience may lead to changes that at least mitigate the dangers involved in dealing with ammonium nitrate in the future.  

Sources:  I referred to the Wikipedia articles “Energy density,” “Ammonium nitrate” and “Ammonium nitrate disasters” as well as Google maps of the vicinity and photographs in various publications of the disaster site, and the book The Science of High Explosives by Melvin A. Cook (Reinhold, 1958).