O-172 Turning up the Heat: Science of CookOff Workshop Findings

September 2016
Dr Matthew Andrews
Cookoff, with respect to munitions safety, is one of the most difficult of the insensitive munitions tests to form a standardised test that reflects a real accident scenario. Currently cookoff is bookended by a slow and fast heating regime. In an accident scenario the transfer of heat to a munition from a heat source is affected by a multitude of parameters (distance, surroundings, orientation of the munition, material properties, rate of heat transfer etc). It is a dynamic situation and the subsequent reaction(s) to the energetic material(s) within the munition will be affected by an array of parameters. Progress has been made to understand the threat; the most recent example of this has been the work by the NATO Custodial Working Group (CWG) on Fast Heating (Chassagne, et al., 2015). This work, through the characterisation of the fuel fire, has aimed to understand how heat is transferred into a munition when different fuel sources (gas, liquid) are used. Large strides have been made through these efforts into the scientific understanding of the fast heating environment. The uses of scientific understanding (physics, chemistry and engineering principles) have been applied to the problem and sequentially this can guide the development of the standard. For the slower rates of thermal deposition into a munition the problem becomes more complex. Therefore research into understanding both the threat and the processes associated with cookoff have to be undertaken. MSIAC, and its former entity NIMIC, have organised a number of workshops relating to cookoff (FitzGerald-Smith, et al., 1993) (Stokes, et al., 1996) (Peugeot, et al., 2003) but a concerted effort in this area has not taken place since 2002. In the intervening years numerous of papers related to cookoff mechanisms [thermal threat, ignition, growth, damage, etc; (Parker, et al., 2005) (Asay, et al., 2004) (Hobbs, et al., 2014)] and modelling (Cook, et al., 2013) (Gross, et al., 2015) have been published and a seminal text on non-shock initiation of energetic materials (Asay, 2010) included a chapter on cookoff (§7). Within in this chapter Asay states that cookoff is “a very complicated series of events” and goes on to describe how the thermal source affects the energetic material, and how in turn chemical reactions lead to decomposition products (gases, liquids) that affect damage to the material and the resultant level of reaction (violence). Interest in slow cookoff (as a threat) has grown with a number of organisations raising the question as to the suitability of the current standard to reflect the threat. To answer this difficult question a number of avenues of research need to be undertaken. One of these streams was tasked to MSIAC to organise a workshop associated with cookoff. As with other recent standards, generation/updates of a standard should be guided by both the real scenario and scientific understanding of the problem.

In April 2016 MSIAC held the Science of Cookoff (SoCO) workshop in Atlanta. This was a five day workshop aimed at discussing the complex problem of cookoff. The objectives for the meeting were to improve the understanding of cookoff of energetic materials and their systems. These objectives were to be achieved through discussions and presentations on chemical and physical changes, heating rate and heating conditions, critical ignition and growth conditions, reaction phenomenology, models and modelling, and sub-scale testing to system-level tests.

The five day workshop started with state of the art presentations from subject matter experts from across the MSIAC community. The topics covered aspects of cookoff – ignition and growth, material damage, kinetics and material properties, violence of reaction, scaled tests for understanding cookoff, modelling and test hierarchy. These hot topics were then discussed in detail over the following three days. The workshop concluded with a summary of all findings and specific outputs for the community. The aim of this paper is to provide an overview of the main workshop findings and how the objectives of the workshop were met.

This paper is a summary of the final workshop report, which will be issued as an MSIAC limited distribution document. This paper will also touch upon the gaps in understanding, how to apply our collective knowledge and tools (tests and models) to improve design and assessment of munitions response to cookoff and what the understanding is of heating rate effect.

Contact us for more information: 

Dr Matthew Andrews
United Kingdom
+32 2 707 56 30
  • Dr Michael Sharp
  • Emmanuel Schultz
  • Wade Babcock