Committee of Experts on the Transport of Dangerous Goods and on the Globally Harmonized System of Classification and Labelling of Chemicals

Sub-Committee of Experts on the Transport of Dangerous Goods

Forty-first session

Geneva, 25 June – 4 July 2012

Item 2 (d) of the provisional agenda

Explosives and related matters: DDT Test and Criteria for flash composition

A follow on report on the comparison of the results obtained for a set of pyrotechnic compositions subjected to the HSL Flash Composition Test and the proposed USModified DDT Test

Transmitted by the expert from the United Kingdom

I. Background

1.  At its 37^th and 39^th sessions the Sub-Committee considered papers regarding the proposed new US modified DDT Test and Criteria for flash compositions (see informal documents SCETDG/37/INF.34  UN/SCETDG/39/INF.16; UN/SCETDG/39/INF.22; UN/SCETDG/39/INF.30 and UN/SCETDG/39/INF.44 and document ST/SG/AC.10/C.3/2010/31 transmitted by the experts from the Germany; Japan; United States of America and the United Kingdom).

2. In its reports to both the 37^th and 39^th sessions (informal document SCETDG/37/INF.73 and SCETDG/39/INF.58) the Working Group on Explosives noted that it would be desirable to have both the HSL Flash Composition Test (T-P test) and the US Modified DDT Test (DDT test) test performed on samples so that the results could be evaluated as to whether the tests provide comparable results.

3. The experts from the United Kingdom and Japan also observed that their work indicated that further work on granular compositions might identify whether or not the United States of America modified DDT Test is a suitable method for discriminating “Flash composition” as defined in the notes to 2.1.3.5.5 of the Model Regulations from “non-flash compositions” used as a bursting charge etc. in fireworks.

4. The expert from the United Kingdomreports here on further results from a second round of work that was commissioned from the Health and Safety Laboratory (HSL) to compare the performance of samples of pyrotechnic compositions in both the HSL Flash Composition Test and the US Modified DDT Test.

II. Follow on testing

5. The second round of work conducted by HSL used compositions from the same set of samples that were reported in informal document SCETDG/39/INF.30 with the addition of six further compositions comprising a range of types of pyrotechnic mixtures. These additional samples were selected using the same criteria as detailed in informal document SCETDG/37/INF.34. i.e.:-

•  Presenting a range of actual or expected performances in the T-P test;

•  Representing a range of compositions with the potential to be encountered as burst charges in fireworks;

•  Representing a range of particle sizes;

•  Representing a mixture of granular and finely divided compositions.

6. The sample selection also took account of the comments of the expert from the Netherlands in the report of the Working Group on Explosives to the 37^th session and  the comments of the expert from the United Kingdom in the informal paper SCETDG/37/INF.34 in relation to:-

•  The broader types of composition that can be regarded as flash according to the description in Note 2 to 2.1.3.5.5 of the Model Regulations;

•  The potential for the proportion of flash contained within a firework to be used to determine its likely hazard division.

7.  Details of all the compositions are summarized in annex 1.

III.  Comments on the second round of testing undertaken by HSL

8.  The expert from the United Kingdompreviously reported that the USmodified DDT Test procedure contained a number of discrepancies (informal document SCETDG/39/INF.30).

9.  During the follow-on testing a further discrepancy was identified between the description and the actual assembly of the cap/cover and what could be physically manufactured. This related to the weight of the confining cover or cap (sleeve), stated as approx. 2.87 kg whereas the confining cap produced by HSL which was made in accordance with ST/SG/AC.10/C.3/2010/31, was 102 mm in diameter and weighed 10.87 kg.

10.  It is noted that the cap had been reduced in diameter to 63 mm in informal document SCETDG/39/INF.44, which would give a weight of approx. 2.87 kg.

11.  The second round of comparison testing carried out by HSL was conducted using the same equipment used to generate the data reported in informal document SCETDG/39/INF.30 and is detailed below:

•  Cardboard tubes for the sample were 152 mm long, 25 mm internal diameter, 3.5 mm wall thickness, and closed off with 1 mm thick card;

•   Spiral wound sample tubes were used instead of convoluted tubes to ensure consistency with the previous round of testing;

•   A mild steel tube of 38 mm internal diameter, 102 mm outside diameter, 190 mm long with an internal pocket 152 mm deep was used, approx. weight 10.87 kg;

•   A Nobel’s Vulcan fusehead was used to fire the sample,

•   All samples were screened through a 425 micron sieve unless the sample was too coarse (indicated in the results table in annex 1).

12. As was noted in informal document SCETDG/39/INF.30 the 190 mm long mild steel tube was used because there were concerns that a shorter tube, would result in the limited end thickness of the sleeve presenting potential safety issues.

 IV. Consideration of the Results

13.  A tabulated comparison of the test results can be found at annex I. The tabulated comparison includes the data from the previous round of testing.

14.  It is noted that the cap (cover) used by HSL was heavier than the updated test proposed by the expert from the United States (informal document SCETDG/39/INF.44) but that similar results were nevertheless obtained.

15.  In samples which are close to the cross over threshold as designated “Flash”/”Not Flash”, the weight of the cap may have implications, in that a lighter a cap would enable a sample to be considered “-” whereas a heavier a cap could result in a “+”. It is postulated that the degree of confinement produced by the heavier cap may result in the test sample developing such a performance as to make it more likely that the witness plate is punctured before the cap can lift, reduce the pressure or its rate of increase and thereby reduce the burning rate of the substance under test. 

16.  Within the tests conducted by HSL, three samples did not give uniform responses. Sample 3 gave a “-” result in four out of six shots; Sample 4 gave a “+” result in three out of four shots and Sample 8 gave “-” result in five out of six shots. These results indicate that there can be a variable response at or around the “DDT” threshold.

17.  It is observed that Samples 3 and 8 are conventional blackpowders and both gave a “+” response in the DDT test.

18.  Similarly there was some variability in the damage to the witness plate between different runs for several of the samples. These responses are described in detail in the footnotes to annex I.

19.  The table below comprises a comparative risk ranking between the two techniques. It is observed that there is generally good correlation between the performance rankings obtained from the two techniques.

20.  There was however a discrepancy between the rankings obtained from the blackpowder substitute in the DDT test (“-“) and T-P Test (average Rise time 3.62ms).

Table (English only)

V.  Conclusions

20. The objective of the requirements of Note to 2.1.3.5.5 of the Model Regulations appears to be to ensure that fireworks classified according to the use of the default table do not include compositions that would present an enhanced hazard, different to that which would be expected purely from the fireworks’ size and construction.

21. Both the US DDT test and the HSL T-P test provide methods to identify compositions, both powdery and granular, that could, if they were included in fireworks, present an enhanced hazard i.e. comprise “flash compositions”.

22. The degree of variability of response in both the US DDT test and the HSL T-P test are such as to indicate that threshold effects could, in some circumstances, be significant and that there is therefore value in taking a precautionary approach towards using an individual technique as the sole mechanism for identifying a composition as not comprising “flash”.

VI.  Proposals

23.  The expert from the United Kingdomasks that the Working Group on Explosives considers introducing the Modified US DDT Flash composition test described at annex II as a new Appendix 8 to the Manual of Tests and Criteria.

24.  The expert from the United Kingdom asks that the Working Group on Explosives considers whether the results of these further comparative tests indicate that the adoption of criteria in the Model Regulations combining the results from both the HSL Flash Composition Test and the US Modified DDT Test would have value by reducing the uncertainty around threshold effects and whether the Note to 2.1.3.5.5 can be revised to:

“Flash composition” in this table refers to pyrotechnic substances in powder form or as pyrotechnic units as presented in the firework that are used to produce an aural effect or used as a bursting charge, or lifting charge unless:-

(a)  The time taken for the pressure rise is demonstrated to be more than [6]ms for 0.5g of pyrotechnic substance in the HSL Flash Composition Test in Appendix 7 of the Manual of Tests and Criteria;

(b)  The pyrotechnic substance gives a negative result in the Modified US DDT test in Appendix 8 of the Manual of Tests and Criteria; or

(c)  The time taken for the pressure rise is demonstrated to be more than [4]ms for 0.5g of pyrotechnic substance in the HSL Flash Composition Test and the pyrotechnic substance gives a result in the Modified US DDT test that is no more severe than [a simple tear in the witness plate  which is no more than 10mm in length in each of 3 “+” runs and which is, in each case,  aligned with the circumference of the supporting steel ring].

Annex I

               Results of Comparative Tests including follow-on tests

Annex II

DDT Flash Composition Test

1.  Introduction

This test is used to determine whether pyrotechnic substances in powder form or as pyrotechnic units as presented in fireworks, that are used to produce an aural effect, or used as a bursting charge or lifting charge are considered to be flash composition for the purposes of determining the classification of fireworks using the UN default fireworks classification table in 2.1.3.5.5 of the Model Regulations.

2.  Apparatus and materials

2.1  The experimental set up for the DDT Flash Composition Test is shown in Figure 1.

2.2  A twenty-five (25) gram sample of a loose powder confined in either:

   a)  A heavy-wall cardboard convolute sample tube with an inside diameter of  25.4mm and height 152 mm with a maximum wall thickness of 3.8 mm,

   or

   b)  A spiral wound cardboard sample  tube with an inside diameter of 25.4mm  and height of 152mm with a maximum wall thickness of 3.5mm, closed at the base  with a paper or thin cardboard cap or membrane just sufficient to retain the sample.

2.3  The ignition source is provided by an electric match-head inserted centrally in the top of the explosive sample in the tube to a depth approximately equal to its length.

2.4  Surrounding the sample tube and also resting on the witness plate is placed a  rugged mild steel confinement cover or “cap”with inner walls and head section approx. 32 mm thick with an inside diameter of  38 mm, an outside diameter of  between 63 mm and 102mm and a height of  between 185 mm and 190 mm and weighs between approx. 2.9 kg and approx. 10.9 kg.  Below the sample tube and surrounding steel confining cap is the square shaped steel witness plate, which is 1.0 mm thick and at least 152 mm on edge. The steel witness steel plate is then placed on a steel ring of approximately 51 mm height with an inner diameter of 90 mm and 3.5 mm wall thickness. The apparatus is placed onto a square shaped steel base plate of approx. 13 mm thickness and 152 mm on edge.

3. Procedure

3.1  The sample compositions are uniformly mixed and then twice passed through either

      (a)  A Number 40 mesh screen; or

      (b)  A 425 micron sieve

except where the nature is clearly granular in nature and is too coarse for the mesh or sieve. 

3.2   Twenty-five (25) grams of the candidate substance tested is weighed into the cardboard sample tube.  It should fill the sample tube somewhere between 1/3 and 2/3 full, depending on its density. For free-flowing granular substances, the sample is consolidated by allowing the tube to fall vertically through a height of 51 mm.

3.3   In all cases, the final density of the explosive in the tube should be as close as possible to its density in a fireworks device.

3.4   Those explosives whose sensitivity could be moisture dependent should be stored for at least 24 hours in desiccators at a temperature of 28 - 30 °C prior to testing.

3.5   The sample tube is placed in the centre of a heavy steel confining sleeve fixture shown in the diagram in Figure 1. which rests on the witness plate, steel ring and steel base plate. The electric match-head is inserted centrally into the top of the explosive formulation. The electric match-head igniter is then initiated from a safe position.

3.6   After initiation and a suitable interval to allow for falling debris, if any, the witness plate is recovered and examined. The test is conducted three times or until a positive result is achieved.

 4.  Test criteria and method of assessing results

4.1   The result is considered "+"  and the substance is considered to be a “flash” composition if in any trial the witness plate is torn, perforated, pierced or otherwise penetrated (i.e. light is visible through the plate). Bulges or folds in the witness plate are not to be considered to be “+” results.

4.2   Otherwise, the result is considered “-“.

联合国危险货物运输专家和全球化学品统一分类和标签制度专家委员会

危险货物运输专家分委员会

第四十一次会议

日内瓦, 2012年6月25日 – 2012年7月4日

议程第2 (d) 项

爆炸物和相关内容: 闪光成分的DDT 试验和标准

关于按照HSL闪光成分试验和提议的美国改进DDT试验方法得到的一组烟火成分结果比较的后续报告

由英国专家提交

I.  背景

1.   在第37和39次会议上，分委会考虑了关于闪光成分的新的美国改进 DDT试验和标准的建议（见非正式文件SCETDG/37/INF.34 UN/SCETDG/39/INF.16; UN/SCETDG/39/INF.22; UN/SCETDG/39/INF.30和UN/SCETDG/39/INF.44以及文件ST/SG/AC.10/C.3/2010/31，由德国、日本、美国和英国专家提交）

2.  在37和39次会议的爆炸品工作小组报告中(非正式文件SCETDG/37/INF.73 和SCETDG/39/INF.58)，他们注意到，值得对样品进行HSL闪光成分试验（T-P试验）和美国改进DDT试验（DDT试验），结果可以用作评价这些试验是否可以得出可比的结果。

3.  英国和日本的专家也发现他们的工作表明对颗粒组分更深入的研究可能可以确认美国改进DDT试验是否是区分“闪光成分”与烟花中用作爆炸药的“非闪光成分”的合适方法，闪光成分在规章范本2.1.3.5.5的注释中有定义。

4.  英国专家在这里报告了第二轮工作的进一步结果，这一工作受健康与安全实验室(HSL)委托，目的在于对比烟火剂成分样品在HSL闪光成分试验和美国改进DDT（爆燃转爆轰）试验中的特性。

II.    后续试验

5.  HSL进行的第二阶段的工作用来自同一套样品的成分，这一样品在非正式文件SCETDG/39/INF.30中报告过，同时还有六个另外的成分，组成一系列的烟火剂混合物类型。试验同样的标准选择这些附加样品（在非正式文件SCETDG/37/INF.34中有详细介绍），即：

•  T-P试验中，在实际或预计性能范围内具有一定代表性的样品；

•  有可能作为烟花中爆炸药的一系列组分的代表性样品；

•  一系列的粒度分布的代表性样品；

•  颗粒和磨碎组分混合物的代表性样品。

6.  样品的选择也考虑了荷兰专家的在爆炸品工作小组37次会议报告中的评论以及英国专家在非正式文件SCETDG/37/INF.34中的评论，涉及到：

•  根据规章范本2.1.3.5.5中注释2的描述，可以被认为是闪光成分的更广泛类型；

•  烟火中闪光成分含量的比例用于确定其危险类别的可能性。

7.  所有组分的详细情况在附件1中概述。

III.  对HSL进行的第二轮试验的评论

8.  英国专家先前报告美国改进DDT试验程序中有一些不一致之处（非正式文件SCETDG/39/INF.30）。

9.  在后续试验中，在盖帽/盖子以及可以物理加工的描述和实际装配之间发现了进一步的差异。这与封闭的盖子或者盖帽（套筒）质量（大约2.87kg）有关，然而HSL根据ST/SG/AC.10/C.3/2010/31制作的密闭盖子直径102mm，质量10.87kg，。

10.  非正式文件SCETDG/39/INF.44中帽盖直径已经减小到63mm，大约重2.87kg。

11.  HSL进行的第二轮对比试验用了与非正式文件SCETDG/39/INF.30中得出的数据相同的设备，具体如下：

•   装样品的硬纸管长152mm，内径25mm，壁厚3.5mm，并用1mm厚的硬纸板密封；

•   使用螺旋型绕制的样品管代替旋转套管，以确保与前一轮试验的一致性；

•   使用内径38mm，外径102mm，长190mm，内口深152mm的低碳钢管，大约重10.87kg；

•   使用Nobel’s Vulcan引信头点燃样品，

•   所有的样品用425μm的筛过筛，除非样品太粗（见附录1的结果表格）。

12.  正如SCETDG/39/INF.30中所注，使用190mm长的低碳钢管是因为注意到若使用较短的管子，可能会因为套筒末端厚度有限的原因而形成潜在的安全问题。

IV.  结果的思考

13.  附件1表格中列出了试验结果的对比。表中的对比包括前一轮试验的结果。

14.  值得注意的是， HSL使用的盖帽（盖子）比美国专家提议的更新过的试验中使用的要重（非正式文件SCETDG/39/INF.44），但是却得到了类似的结果。

15.  在接近于指定“闪光”/“不闪光”的临界值的样品试验时，盖帽的重量可能有影响，因为轻的盖帽将使样品判为“-”，而重的盖帽将导致样品判为“+”。有人推测，由较重的盖帽产生的密闭等级可能导致样品产生一种效果，就是使验证板在盖帽升起前就被炸穿，减小压力或者压力上升的速率，因此减少试验中物质的燃烧速率。

16.  HSL进行的试验中，三个样品未能得出一致的结论。样品3在6次的试验中4次得出“-”，样品4在4次试验中3次得出“+”，样品8在6次试验中5次得出“-”。这些结果表明在“DDT”临界值或者其附近，结果是不确定的。

17.  可以看出，样品3和8为传统的黑火药，在DDT试验中均得出“+”的结果。

18.  类似的，几个样品在几次试验中对验证版的损坏也是变化的，这些现象详细记录在附录1的附注中。

19.  下面的表格包括了两种方法间的风险等级对比。可以看出，一般两种方法获得的性能等级有不错的关联。

20.  但是，黑火药代用品在DDT试验中（“-”）和T-P试验中（平均上升时间3.62ms）得出的等级上有矛盾。

表

 V.  结论

20.  规章范本中2.1.3.5.5中注的要求目的应该是确保烟花根据设定表进行正确的分类，但不包括具有危险性更大的组分，这些组分的危险性与单纯从烟花的尺寸和构造来判断的危险性不同。

21.  美国 DDT试验和HSLT-P试验均给出了识别可能呈现增大危险性（如果包含在烟花中）成分的方法，包括粉末和颗粒，比如包括“闪光成分”。

22.  美国 DDT试验和HSL T-P试验中反应的不确定程度已经表明临界效应在某些情况下很重要，因此采取预防措施，避免使用单一方法作为唯一的机制识别某组分不含“闪光成分”是有价值的。

 VI.  提议

23.  英国专家要求爆炸品工作小组考虑引进附录2中描述的改进US DDT闪光成分试验作为试验和标准手册新的附录8。

24.  英国专家要求爆炸品工作小组考虑，规章范本中的标准同时采用HSL闪光成分试验和美国改进DDT试验的结果，这些进一步的比对试验结果是否有利于减少临界效应的不确定性，以及2.1.3.5.5中注释是否可以修订为：

本表中“闪光成分”，是指粉末状的烟火物质，或烟花中用于产生响声效果、用

作爆炸药或弹射药的烟火装置，除非：-

(a)   在《试验和标准手册》附录7的HSL闪光成分试验中，每0.5克烟火物质显示升压所需的时间大于 [6]毫秒；

(b)   在《试验和标准手册》附录8的改进美国 DDT试验中呈现阴性的烟火物质；或者

(c)   在HSL闪光成分试验中，每0.5克烟火物质显示升压所需的时间大于 [4]毫秒，并且在改进US DDT试验中未达到以下剧烈程度：[在配有支撑钢环时，3个“+”阳性结果的见证板有不大于10mm长度的简单撕裂]

附件I

后续试验的结果对比

附件2

DDT闪光成分测试

1. 介绍

本试验用于确定烟花中用于产生声响效果、用作爆炸药或弹射药的粉末状态的烟火物质或烟火装置，对使用《规章范本》2.1.3.5.5中联合国设定的烟花分类表、确定烟花分类目的而言，是否可作为闪光成分。

2.  设备和材料

2.1  DDT闪光成分试验用设备见图1。

2.2  将25g疏松粉末状样品装配至以下任一装置中：

a)   一个厚壁的硬纸板制回旋样品管，内径25.4mm，高152mm，最大壁厚3.8mm，

 或

b)   硬纸板制螺旋型绕制的样品管，内直径25.4mm，高152mm，最大壁厚3.5mm，并在底部用纸或者薄纸板盖或薄膜密封，只要能够支撑住样品即可。

2.3   点火源由电子火柴头提供，将其插入管中爆炸样品顶部中心，深度大约等于其长度。

2.4   放置一个坚固的低碳钢密封盖或者“盖帽”包围样品管，并搁在验证板上，其内壁和顶部界面大约32mm厚，内直径38mm，外直径63mm至102mm，高185mm至190mm，重约2.9kg至10.9kg。样品管下方，包围钢密封盖的是方形钢验证板，厚1.0mm，边长至少152mm。钢验证板置于一个钢圈上，大约51mm高，内直径90mm，壁厚3.5mm。仪器放置在一个方形钢基座板上，约12mm厚，边长152m。

3.  程序

3.1  样品组分混合均匀，然后两次通过下面任一筛子：

(a)  40号筛；或

(b)  425μm筛

除去本来就是明显的颗粒状物质和相对于筛子太粗的物质。

3.2   称取25g待测物质，装入硬纸板样品管。将样品管根据样品密度装填至1/3与2/3之间。对于能够自由流动的颗粒状物质，将管子从51mm高处垂直落下以夯实样品。

3.3   在所有情况下，最终爆炸品在管中的密度应尽可能地接近烟花装置中的密度。

3.4   敏感度与水分有关的爆炸品试验前应储存在28 - 30 °C干燥器中至少24小时。

3.5   样品管置于一个重钢密封套筒中间，如图1中所示，套筒搁在验证板、钢圈和钢底座板上。电子火柴头插入爆炸品顶端的中心处，可以从安全的地点将其点燃。

3.6   考虑到残余的碎片，起爆后等待一段时间，如果有的话，找到验证板并检查。试验进行三次，直到得到阳性结果。

4.  试验标准和结果评价方法

4.1   如果任何一次试验中验证板撕裂、穿孔、穿透或者其他情况的穿透（比如光可以通过验证板）结果即为“+”，物质为闪光成分。验证板凸起或者折叠不认为结果是“+”。

4.2   否则，结果为“-”。