How a student unintentionally made an explosive at U Bristol

motm-TATP-TWLast week, the Safety Zone reported that a University of Bristol student had unintentionally made approximately 40 g of triacetone triperoxide (TATP), prompting building evacuations and a controlled detonation by an explosives team. Here’s a statement about the incident, prepared by Timothy C. Gallagher, a chemistry professor and dean of the Faculty of Science, and Nicholas C. Norman, head of the school of chemistry.

On 3 February 2017, a graduate student in the School of Chemistry at the University of Bristol was carrying out a literature procedure to oxidise an aldehyde to the carboxylic acid using aqueous acidified chlorite. The experiment was carried out on a 5 mmol scale (just under 1g of aldehyde) and risk assessments identifying all hazards had been undertaken and signed off by both student and supervisor. The reaction solvent was acetone (50 mL).

Part of the procedure involved adding a quantity of 30% hydrogen peroxide (H2O2) solution to remove some of the by-products of the reaction, whose presence was (apparently) associated with a yellow colour (possibly including chlorine dioxide). The literature indicated that H2O2 be added until this yellow colour had disappeared, which should have required about 1 mL of peroxide solution.

The student, focusing on the yellow colour, which did not completely disappear, continued to add hydrogen peroxide solution until about 50 mL had been added. During workup to remove the solvent, the student realised that the solvent volume was not decreasing and that the liquid was becoming viscous, and so likely contained far more “product” than was expected. GCMS analysis indicated the presence of triacetone triperoxide (TATP), and it was estimated that this could amount to 30-40g if all the excess H2O2 had reacted with the acetone solvent.

At that point, the graduate student immediately alerted the supervisor, who escalated this to the Head of School. A series of decisions were made and actions taken that resulted in the disposal of the suspected TATP by means of a controlled explosion carried out by the emergency services.

Nobody was injured and no damage was done in the lab. Although the TATP presented an explosion hazard, the risk of explosion was considered minor due to all material remaining in solution; TATP is far more sensitive to detonation as a solid. Immediate disposal was warranted, however, due to the risk of precipitation/crystallisation of a solid material.

There are lessons to be learned from what happened and some messages.

First, the student was concerned with adding hydrogen peroxide to remove the yellow colour (due, at least in part, to chlorine dioxide, which is itself a hazardous material), but overlooked the much greater hazard of adding a large amount of hydrogen peroxide to a reaction containing acetone as the solvent. The student overlooked the hazard despite the fact that the potential formation of TATP had been identified in the original risk assessment. This illustrates how focus in one area can lead to ignoring another even though the consequences of the other are known.

Secondly, and linked to the first lesson, the role of the solvent (acetone) was also overlooked—solvents are often regarded as benign–although again the presence of acetone and the risks associated with that in the presence of H2O2 had been identified.

However, and this is critical, having realised what had happened, the graduate student immediately took the action needed to mitigate a potentially dangerous situation, rather than delaying or, worse, trying to cover it up. This was highly responsible – the most important thing done – and shows the value of investing in developing and fostering a culture in which colleagues recognise errors and misjudgements, and they are supported to report near misses.

The airline industry can teach us a lot in this regard. The necessity of having a “safe period,” during which one can report a near miss without penalty, is essential. Clearly, reckless behaviour is unacceptable, but we don’t believe this was the case here. Rather, it was more around a lapse in concentration, which (if we are honest) we are all capable of. The actions taken once the issue had been identified are, for us, key to the culture we are striving to foster for openness in reporting accidents and incidents. There is no question of action being taken against a graduate student whose positive actions have been recognised.

However, in future, we are instituting more stringent risk assessments, and checking of those assessments, for any reaction involving hydrogen peroxide. Specifically, this will involve preparing an individual risk assessment for hydrogen peroxide even if its use in a reaction is only minor. All such assessments will then be subjected to additional scrutiny.

Other commentary: Chemjobber, Reddit Chemistry, In the Pipeline

Author: Jyllian Kemsley

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5 Comments

  1. The font you use is extremely light and difficult to read (and I’m only 25!). Please don’t use the light weight of this typeface!

  2. @Anastasia–I forwarded your comment to the person in charge of the blog design. I think that you’re the first to let us know that the font is a problem.

  3. The font in the blog is too light, even tho’ the style is clear. Jyllian, the date under your name/comment is almost invisible.
    However, when some of the blog text is selected and printed, the printed font is of good intensity (good contrast).

  4. Supposed to add 1 ml + Actually added 50 ml = Lapse of concentration.

  5. This story reminds me of an accident which was reported to me years ago by a colleague. It involved the preparation of trimethylamine oxide by a third-year student. The experiment is very simple, it had been carried out numerous times without any problems. Aqueous solutions of Me3N and a slight excess of H2O2 were to be combined and left to stand overnight. Then the mixture should have been evaporated to dryness on a steam bath until the product Me3NO x 2 H2O is left as colorless crystals. The steam bath had been removed from the lab in the course of an extensive renovation, so the student used a rotary evaporator instead. This resulted in a fierce explosion which totally destroyed the rotavap and caused considerable damage to the lab. Luckily no personal injuries were incurred. What had happened? The reaction is quite slow and not complete after 15 hrs. When the mixture is heated on a steam bath, any left Me3N will evaporate while the excess of H2O2 decomposes before it reaches dangerous concentrations. However, when evaporated under vacuum near room temperature, H2O2 can be concentrated to up to 90% where it becomes a treacherous explosive, particularly in the presence of oxidizable organic material. Clearly, even minor changes to a time-proven procedure can have quite unexpected and sometimes serious consequences. In this (and all other cases involving peroxides) a suitable test should be performed before workup, and, if positive, appropriate measures should be taken to get rid of any residual peroxide.