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 3 (b) of the provisional agenda

Listing, classification and packing: miscellaneous

Classification of Self- Reactive substances

Transmitted by the Dangerous Goods Advisory Council (DGAC)

Introduction

1.  It has come to DGAC’s attention that there may be inconsistencies in classification practices regarding self-reactive substances (SRS) and that some practices appear to deviate from the classification system as described in the Model Regulations.  In the interest of greater international uniformity, DGAC offers this paper as a basis for discussion.  In particular, it appears some monomers that have the potential to polymerize are being classified as self-reactive substances. Considering the historical classifications of monomers with a potential to polymerize, the definition for SRS, and the current provisions for materials that must be transported in a stabilized condition, DGAC questions whether the practice of classifying monomers with a potential to polymerize as SRS is correct.

2.  Historically substances that have a potential to polymerize have been assigned to the hazard class representing the primary hazard (e.g., Division 2.1, Class 3 and Division 6.1). Examples include UN 1086 vinyl chloride, UN 1301vinyl acetate, UN 1303 vinylidene chlorine and UN 3073 vinylpyridenes (a more extensive list of approximately 45 named substances may be found in document ST/SG/AC.10/1998/10. Shipping names for these substances typically include the word “STABILIZED” as described in 3.1.2.6 and 5.4.1.5.4 and the term stabilized is defined in the glossary as:

“Stabilized in relation to polymeric monomers means that the substance is in a condition that precludes uncontrolled polymerization. This may be achieved by methods such as the addition of an inhibiting chemical, degassing the substance to remove dissolved oxygen and inerting the air space in the package, or maintaining the substance under temperature control.”

If stabilization is by temperature control, control and emergency temperatures must be provided on the transport document. While temperature control may be required to safely transport these substances, it is important to note that the 45 named substances were never subjected to SRS classification testing as part of their classification. 

3.  The UN text for self-reactive substances suggests that polymerizing substances do not fall within this category. The definition of self-reactive substances in 2.4.2.3.1.1 limits self-reactive substances to substances that are “liable to undergo a strongly exothermic decomposition”. The minimum criteria for considering a substance for classification as self-reactive in 2.4.2.3.1.1(d) includes a criterion of a heat of decomposition of 300 J/g. In 2.4.2.3.1.1(e) a Self-Accelerating Decomposition Temperature (SADT) of 75C is referenced.  In addition, in paragraph 2.4.2.3.1.2, the properties of self-reactive substances are described.  This text also refers to the potential for a decomposition reaction and identifies example chemical structures that are prone to reactive decomposition. Substances in the SRS table all appear to be liable to decomposition. 

4.  Paragraphs 3.1.2.6 and 5.4.1.5.4 were introduced on the basis of ST/SG/AC.10/C.3/1999/81 by the expert from the United Kingdom.  It is clear from this document that these paragraphs were included to take account substances that polymerize.  Paragraph 3.1.2.6 requires that for substances, other than self-reactive substances and organic peroxides, the word STABILIZED be included in the proper shipping name of substances that are liable to dangerously react.  The example shows the word stabilized associated with a toxic liquid.  The requirements would seem to imply that a consignor is permitted to self-classify a unnamed polymerizing substance.  For unnamed substances, shipping descriptions such as:

“UN 1993 Flammable liquid, N.O.S, stabilized”

“UN 3082 Environmentally hazardous substance, liquid, stabilized”

would seem possible, where the substance meets one of the hazard criteria. But a deficiency of the current text is that it does not provide for a proper shipping name for substances that pose only a polymerization risk and meets none of the criteria of the Model Regulations.

5.  Resins are one group of materials which may only pose a polymerization risk. In some cases resins are transported with a hardener already added. During application at the destination they are allowed to exothermically cure. They may be transported under cooled conditions. These and others react at low temperatures and sometimes have a reaction energy slightly above 300 J/g.  However, violent reaction is not a characteristic of these types of substances.  In fact, considering their use as thermally setting plastics, propensity to deflagrate or detonate are not desirable properties.  It may be that the heat of polymerization leads to a heating of the resin to a point where entrained water is vaporized but no other gases are produced.    What do the words “dangerously react” mean in the context of such materials where the only hazard is polymerization? What shipping name should be assigned?

6.  It is DGAC’s opinion that application of SRS testing is not intended by the current provisions and that such testing is more than what is needed.  Considering their degree of risk, it would seem that the consignor should continue to be allowed to self-classify these substances.  To provide greater uniformity, criteria should be provided and a shipping name for substances with no hazard other than polymerization should also be provided.

7.  Based on the above, we would welcome discussion by the Sub-Committee on the following:

(a)  Should substances that polymerize be classified as SRS?

(b)  Are the test methods for SRS appropriate?  For substances that exothermically self-react by polymerization (e.g., an SADT of 50C or less and a heat of reaction of more than 300 J/g) could more limited testing suffice (e.g. a time pressure test (Test Series C))?

(c)  Considering the low degree of risk, is it necessary for polymerizing substances to be classified by the competent authority or should continued classification by the consignor be permitted?

(d)  What proper shipping name should be assigned if such a substance poses no other hazard than polymerization? How should it be classified?

If appropriate, DGAC would prepare a written proposal for the 42^nd session on the basis of the Sub- Committee's comments.

Note:Documents ST/SG/AC.10/1998/10 by the expert from the United Statesand ST/SG/AC.10/C.3/1999/81 by the expert from the United Kingdom, are both accessible at http://documents.un.org/.

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-7月4日
议程第3 (b)项

列表，分类和包装：杂项

自反应物质的分类

由危险货物咨询委员会提交(DGAC)

介绍

1.  对于自反应物质在实际分类中不一致的情况引起了DGAC的注意，出现了一些实际情况偏离规章范本所描述的分类程序。为了更广泛的国际统一，DGAC提交了这份提案作为讨论的基础。特别是，有些有聚合倾向的单体会被分类为自反应物质。考虑到有聚合倾向的单体以往的分类，自反应物质的定义以及现有对必须保证其在稳定的状况下运输的物质的现有规定，DGAC质疑将有聚合倾向的单体分类为自反应物质的正确性。

2.   以往对于有聚合倾向的单体物质被划分的危险类别代表了其主要危险性。(例如：2.1项，3类和6.1项)。实例包括UN1086 乙烯基氯，UN1301乙酸乙烯酯，UN1303乙烯叉二氯和UN3073乙烯基吡啶(一份更广泛的列明了近45种物质的列表可在文件ST/SG/AC.10/1998/10中找到)。这些物质正式运输名称的典型特征是在3.1.2.6 and 5.4.1.5.4中描述的包含有“稳定的”字样，在术语中“稳定的”这一术语的定义是：

“稳定的对于聚合的单体的意思是物质出于不可能发生不受控制的聚合的状态，这可以通过添加抑制化学品、除去物质中溶解的氧、将惰性气体装入包件的孔隙或将物质保持在温度控制下等方法做到。”

如果需要温度控制来保持稳定的状态，那么控制温度和危急温度必须在运输单据上体现出来。尽管安全运输这些物质可能需要温度控制，但是值得注意的是45种列明物质从未进行过作为其分类依据的自反应物质分类测试。

3. 在UN文件中建议有聚合倾向的物质不应该属于自反应物质这一类。在2.4.2.3.1.1中对于自反应物质的定义将自反应物质限定为那些“容易发生激烈放热分解”的物质。2.4.2.3.1.1(d)中提到了考虑将一种物质为自反应物质的最低标准，其中包括分解热为300 J/g。在2.4.2.3.1.1(e)中对于自加速分解温度(SADT)的参考值是75℃。另外，在2.4.2.3.1.2段中，描述了自反应物质的性质。这段内容也提到了发生分解反应的可能性并列举了易于反应分解的化学结构。在自反应物质列表中的物质都好像是易于分解的。

4. 3.1.2.6 和5.4.1.5.4段落的引入是基于英国专家提交的文件ST/SG/AC.10/C.3/1999/81。从这份文件中很明显的可以看到这些段落是考虑到了有聚合倾向的物质才引入的。在3.1.2.6中要求除了自反应物质和有机过氧化物，对于易于发生危险反应的物质的正式运输名称中应该包含“稳定的”一词。给出的例子是稳定的一词与毒性液体放在一起使用。这样的要求意味着允许发货人对于未列明的有聚合倾向的物质自行分类。对于未列明的物质，当物质满足其中一项危险标准时，例如：

“UN1993 易燃液体，未另作规定的，稳定的”

“UN3082对环境有害的液态物质，稳定的”

这样的正式运输名称也可以使用。但是现有文件的一个缺点是，对于只有聚合危险而不符合规章范本中其他危险性标准的物质，没有给出适合的正式运输名称。

5.  树脂是一组可能只有聚合危险的物质。在某些情况下，树脂是在已加入固化剂的情况下运输的。在目的地使用时他们允许放热固化。他们可能是在冷却的条件下运输。这些和其他在低温下反应的其他物质，有时反应热稍高于300 J/g。然而，剧烈的反应不是这一类物质的特性。事实上，考虑到他们作为热固性塑料，如果有爆燃或爆炸的倾向是不可取的。可能是热聚合导致树脂加热到一种附带的水被蒸发，但没有其他气体的产生的程度。在文中“危险的反应”的意思对于这种物质来说仅是聚合的危险？应该给予什么正式运输名称呢？

6. DGAC认为现有规定的意图不是使用自反应物质分类测试，这样的测试多过实际的需要。考虑到它们的风险程度，似仍然应该允许发货人自行分类这些物质。为了达到更大程度的统一，应该对除了有聚合危险无其他危险性的物质给出标准和正式运输名称。

7. 基于以上所述，我们希望分委员会讨论以下几点：

(a)  有聚合倾向的物质应分类为自反应物质吗？

(b)  自反应物质测试方法合适吗？通过聚合发生放热自反应的物质(例如，自加速分解温度50℃或者更低以及分解热大于300 J/g)是否进行有限的测试就足够了(例如：时间压力测试(实验系列C))?

(c)   考虑到低风险程度，对于有聚合倾向的物质的分类是否有必要通过主管当局确定或是应该继续允许由发货人来自行分类？

(d)   对于除了有聚合危险无其他危险性的物质应该给予怎样的正式运输名称？应该怎样进行分类？

如果合适，DGAC将准备基于分委员会的评论在第42次会议上提交书面的提议。

注：由美国专家提交的ST/SG/AC.10/1998/10文件和英国专家提交的ST/SG/AC.10/C.3/1999/81都可以在http://documents.un.org/上找到。