Answer to Question #12187 Submitted to "Ask the Experts"

In 1999 there was a fire at a munitions factory in Staffordshire, England, that dealt with depleted uranium (DU). Apparently there was no release of anything serious, but why was there so much worry in the community? "Depleted" sort of infers less dangerous, so was anyone at risk?

I had not heard of this incident before. Attempting to answer these questions gave me an opportunity to learn some new things about the processing of DU. The only information I could find about the fire itself was in an article on a newspaper website. But in summary, the radiation risks from that fire seem to be very low and should be no cause for concern.

Now your first question: Why was there so much worry? The psychology and sociology of the general public's assessment of radiation risk is of great interest to health physicists. Our goal in this area is to give information to individuals, leaders, and the media that will help them realistically assess radiation risks, especially risks due to exposure to low levels of radiation (that is, levels a few times that of background radiation). Our hope is that, as a result, they then will make personal, informed decisions about those risks.

The Health Physics Society (HPS) recently published an update to its brochure, "Radiation and Risk: Expert Perspective." Dr. Joxel Garcia, 14^th Assistant Secretary for Health, US Department of Health and Human Services, wrote the forward for this brochure. In the forward, he references one of the great scientists of the early 20^th century: Madame Marie Curie. Here are the words of Madame Curie, a two-time Nobel Prize winner (physics and chemistry) and pioneer in radiation science: "Nothing in life is to be feared, it is only to be understood. Now is the time to understand more, so that we may fear less." The HPS wants what Madame Curie wanted: more understanding and less fear.

Now to your second question: Was anyone at risk? Risk is in the eye of the beholder, but I believe that most health physicists and industrial hygienists would say that the radiation and chemical toxicity risks to the community from the 1999 fire were and are still very low. The firefighters experienced the greatest risks, but they have training and personal protective equipment to deal with such risks.

According to The Guardian, "uranium swarf caught fire at the Royal Ordnance depot in Featherstone" on 7 February 1999. The article says the plume of smoke reached a height of about 760 meters (m), which indicates a particularly fierce fire. However, "it was believed that there had been no radiation leak although monitoring was continuing. . . . Royal Ordnance said first tests showed that no toxic substances had been released."

Wikipedia says, "Due to its high surface area, swarf composed of some reactive metals can be highly flammable. Caution should be exercised to avoid ignition sources when handling or storing swarf in loose form, especially swarf of pure magnesium, magnesium alloy, pure titanium, titanium alloy, iron, and nonstainless steel." This list should include uranium, which like iron and the others, is pyrophoric. In a different article, Wikipedia says, "A pyrophoric substance . . . ignites spontaneously in air at or below 55 °C (130 °F). Examples are iron sulfide and many reactive metals including plutonium and uranium, when powdered or thinly sliced."

The US Department of Energy (DOE) in the Primer on Spontaneous Heating and Pyrophoricity (DOE-HDBK-1081-94) says, "In the absence of strong drafts, uranium oxide smoke tends to deposit in the immediate area of the burning metal." Conjecturing from the above information, we can find the likely cause of the fire, and it appears indeed that risk was very low and the community should have no cause for concern about exposure to DU that the fire may have released to the local environment.

The HPS produced a fact sheet in 2010 about depleted uranium that is relevant to the current question. Following is a pertinent extract from that fact sheet: "In general, natural uranium and DU are considered to be a chemical hazard to the kidney instead of a radiation hazard. Therefore, inhalation and/or ingestion of these materials should be minimized. However, DU is a radiation hazard when it is inhaled in the form of tiny insoluble particles, which lodge in the lungs and remain there for very long times. DU is less of a radiation hazard than natural U because it is less radioactive than natural U. Direct (external) radiation from DU is very low and only of concern to workers who melt and cast U metal."

The fact sheet concludes, "In summary, some minor health problems have been observed following exposure to DU, but ONLY with high levels of exposure. Exposures to airborne DU or to contaminated soil following military use are not known to cause any observable health or reproductive effects."

How the British authorities handled the residual DU contamination at the munitions factory after the fire might also be of interest. I do not have immediate access to that information, so I refer the questioner to the website of our United Kingdom colleagues in the Society for Radiological Protection. Someone there may be able to help with that question.

In summary, the radiation risks from that fire seem to be very low and should be no cause for concern.

Bob Cherry, PhD, CHP