Discussion on “the assessment of mixture toxicity when the concentration of a certain toxic substance is extremely low”

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This post was last edited by Douman on 2018-6-21 at 17:58. In the design of custom equipment, the category of the equipment is of utmost importance, as different categories require distinct design and manufacturing specifications. However, the toxicity level of the medium is an important criterion for classifying equipment categories. In design work, it is common to encounter mixtures in which some components are non-toxic while only a small portion are toxic. So, how should the toxicity of such mixtures be determined? For example, in the medium of a certain device, only 5% is formaldehyde, while the other gas components are non-toxic and harmless; how then can the toxicity level of this mixed medium be determined? It is believed that most people will adopt the principle of choosing the higher value, and define the toxicity of a mixture as \"highly hazardous\" based on the highly toxic formaldehyde. Of course, this straightforward approach is indeed practical – (there’s no need to worry about the impact of various components; even if one does worry about it, they don’t know how to make a judgment, and even if they can make such a judgment, they’re not sure whether it can be used as a basis). But at the same time, this simplicity also increases the manufacturing cost of the equipment. Regarding the toxicity of mixed media, Appendix A of TSG 21-2016 states the following: it outlines two points – 1, it is unreasonable to adopt a simple approach that assumes higher values rather than lower ones (otherwise there would be no need to include this provision); 2, the regulations delegate the decision-making power to the designers, who are responsible for making such judgments. So, how can the degree of toxicity be reasonably determined? There must always be a basis for calculation Standard A1.2.1 defines the levels of extreme, high, moderate, and low toxicity. What does that mean? Let’s assume we have a sealed 1-cubic-meter container containing a dog, and we start adding a toxic substance to it. The first time we introduce substance A at a concentration of less than 0.1 mg/m3 (for example, 0.08 mg/m3), the dog gets poisoned; therefore, substance A is extremely hazardous ； The second time, when medium B was used at a concentration of <1 mg/m3 (for example, 0.7 mg/m3), the dog became poisoned; thus, medium B is highly hazardous ； On the third attempt, when the concentration of medium C was <10 mg/m3 (for example, 6 mg/m3), the dog became poisoned; thus, medium C constitutes a moderate hazard ； Let’s start over again: it’s still this jar, still this dog, and 5% formaldehyde is being used (100% formaldehyde is highly hazardous). What amount is needed to poison the dog? Converting the concentration level to a volume percentage: Up to this point, one might think that I have provided a calculation method, but it must be admitted that this concept of conversion is merely a process, and there is no verification for it. The author also did not include it in actual work. Forum members will say: Whoa, are you shooting at me? After reading all this, it’s nonsense! It’s the same as not saying anything! Don’t rush; don’t spray me right away. There’s more coming at the end, so you won’t waste your time for nothing. The \"National Training Manual for Design Approval Personnel of Pressure Pipelines\" (3rd edition) provides a method for determining the toxicity level of mixed media, and the author found verification of this method in this manual; see the screenshot. Some forum members might say that since the standards and regulations do not provide a calculation method, can this be used as a basis for assessing toxicity levels? To this question, I can only answer as follows: Everyone has their own understanding; it’s perfectly fine to go for a higher standard rather than a lower one, and there’s no need to worry too much about the exact amount – it varies from person to person. The author is simply sharing this with everyone. As for whether it can be determined, I can’t give an answer either; everyone should make their own judgment. If it is the design agency, ignoring costs, they can simply label it as “highly toxic”. If the manufacturing unit does take manufacturing costs into consideration, it would be reasonable to consider them as appropriate. Whether it can serve as a basis is another matter, but at least it provides a reference. Conversely, if the content is extremely low yet it is classified as highly toxic, where are the regulations and criteria for that? Right? Finally, I’ll provide everyone with the download link for the \"Training Manual for National Pressure Pipeline Design Approval Personnel\" (3rd edition). I posted a sharing thread before. https://bbs.hcbbs.com/thread-1870178-1-1.html