UN test O.1 errors in quantifying the behavior of solid oxidizers Vytenis Babrauskas Fire Science and Technology Inc., San Diego, CA 92103, USA article info Article history: Received 11 June 2015 Received in revised form 1 November 2015 Accepted 1 November 2015 Available online 10 November 2015 Keywords: Ammonium nitrate Fire retardants Solid oxidizers UN test O.1 UN test O.3 abstract The results of the UN test O.1 for oxidizing solids are shown to be incorrect when specimens contain certain inertant additives, illustrated for the case of oxidizers in the ammonium nitrate fertilizer family. Test results for three different AN-based products containing inertants show that two of the three (including calcium ammonium nitrate, CAN, a long-known safer alternative to AN) would be misranked with the O.1 test. An analogy between the heat release rate of substances containing fire retardant (FR) chemicals is established and several ways by which FR behavior can be achieved are demonstrated. It is shown that the O.1 test implicitly adopts only one model of inertant action, and that chemicals which rely on a differing mode of inertant action are liable to be incorrectly treated. It is further shown that the physical basis of the O.1 testdan intimate mixture of finely-comminuted fuel and oxi- dizerdmisrepresents the most common type of accidents involving oxidizers, and that such test results do not correspond to scenarios of a less extreme nature. The new O.3 test improves the analysis method, but does not resolve the problem of excessive commingling of fuel into oxidizer. It is recommended that the intermediate-scale arrangement used by the Bureau of Explosives be adopted for further develop- ment and standardization, in preference to the O.1 or O.3 test arrangements. © 2015 Elsevier Ltd. All rights reserved. 1. Introduction The only standardized test currently used for oxidizer chemicals is Test O.1 (Anon, 2009) in the UN Manual of Tests and Criteria (apart from the new O.3 test, discussed later). The O.1 test is intended to assess the oxidizing propensity of materials in order for them to be classified into Packing Groups for transportation regu- lation purposes. It forms the basis for national regulations in essentially all countries. Apart from the description in the UN book, little research or background for this method has been published. Oxidizing solids, in general, have received very little attention. The former Bureau of Mines (BM) conduced the earliest study (Kuchta et al., 1972) focused on developing a test method, while re- searchers at General Electric (King and Lasseigne, 1972; Hough et al., 1973) expanded and elaborated on the BM work. Those studies, while valuable, are not relevant to the O.1 test, since these workers only used a physical arrangement which was dissimilar to the one eventually adopted by UN. Later, as the UN group had already started its work, Japanese researchers (Uehara and Nakajima, 1985) published a study which, again, was based on a test arrangement dissimilar to the O.1 test. The O.1 test itself is understood to have been evolved by a UN working group which did not publish any documentation on its development work. Subse- quent to the test being finalized, the only published research have been papers by Hasegawa et al. (1989) and Koseki and coworkers (Koseki, 2001; Koseki et al., 2001; Koseki et al., 2002). These papers delve into several standardization issues which are not directly related to the present study. The UN O.1 test involves 30 g of material where the test oxidizer and the cellulose powder and uniformly mixed together, poured into a 70-mm, 60  glass funnel, and inverted into a conical heap on a noncombustible substrate board. A Nichrome wire heater bent into a loop sits near the bottom of the pile. The test entails igniting the fuel/oxidizer mixture by heating the wire to approximately 1000  C. There is only one criterion for judging the results of the O.1 test and that is duration of flaming. Longer duration of burning is assumed to denote lesser hazard due to oxidizer action. For actual classification of chemicals, comparison is made between the test results and a reference oxidizer. In addition, two variants of test have to be run, with 1: 1 and 4: 1 ratios of oxidizer: cellulose. The present study was motivated by a concern over very serious accidents where ammonium nitrate (AN) fertilizer is involved and a fire leads to detonation with disastrous consequences (Babrauskas, 2003; Marlair and Kordek, 2005; Babrauskas, 2016). AN is classified in the UN system as a Division 5.1 PG III solid oxidizer. Adoption of E-mail address: vytob@doctorfire.com. Contents lists available at ScienceDirect Journal of Loss Prevention in the Process Industries journal homepage: www.elsevier.com/locate/jlp http://dx.doi.org/10.1016/j.jlp.2015.11.001 0950-4230/© 2015 Elsevier Ltd. All rights reserved. Journal of Loss Prevention in the Process Industries 39 (2016) 1e6