Question regarding whether nitric acid constitutes a major hazard source
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Recently, I encountered a project involving nitric acid, and I faced some issues regarding its fire hazard and the classification of major hazard sources. The highest concentration of nitric acid used in the project is 58%, while the lowest is 8% during restart operations ； Personally, I have no objection to class B being applied in terms of fire hazard ； However, problems arose in the classification of major hazard sources. According to GB 18218-2018, Table 1 specifies that the critical quantities for fuming nitric acid and nitric acid with a concentration greater than 70% are 20 t and 100 t respectively ； However, in Table 2, for oxidizing liquids and solids, there is another critical amount of 200 tons ； According to the Hazardous Chemicals Classification Information Table, nitric acid is classified as an oxidizing liquid, category three ； But I checked GB 30000.14 again; the criterion for determining oxidizing liquids is that if, when testing a mixture with a mass ratio of 1:1 between the substance and cellulose, the average pressure rise time is less than or equal to that of a mixture with a mass ratio of 1:1 between 65% nitric acid solution and cellulose, then it is not considered an oxidizing liquid. This tank area contains more than 10 nitric acid storage tanks, and the highest concentration in these tanks does not reach 68%. It’s unclear whether they should be classified as major hazard sources. Based on fundamental principles, they should not constitute major hazard sources, but the regulations do not specify the concentration of nitric acid, which is confusing!
Standard GB 18218 does not address concentration
First, the process needs to be determined. Since nitric acid is used, is it purchased externally? Is it still produced by themselves? Whether it is purchased externally or produced locally, it is important to note whether a level of over 70% can be achieved. Then, based on the actual manufacturing processes, an accurate description should be given in the relevant sections; for those cases where the concentration in certain tanks is known, Table 1 should be used, while Table 2 should be applied in other cases. PS: The following are merely my personal opinions, and adjustments must be made in accordance with local requirements. When performing the calculations, simply refer to the information tables – in the case of 30,000, technically speaking, many factors do not need to be taken into account in the calculations. However, when actually producing, using, and storing hazardous chemicals, 30,000 isn’t entirely reliable, as dynamic factors make it difficult to determine precise values. All strict regarding the direct information form
This post was last edited by qugd on 2021-2-1 17:35. Go to hell
First of all, we’re not trying to find loopholes in the rules； Although safety is of utmost importance, one shouldn’t avoid doing things just because of safety concerns ； Secondly, I agree that nitric acid is a strong acid, but here 8% nitric acid is used in large quantities; setting the concentration aside, is it reasonable to talk about the danger associated with acids? Third, if this is not examined carefully and a strict approach is adopted in everything, it will lead to rather absurd situations ； A bunch of acid tanks with extremely low concentration, along with numerous sensors for temperature, pressure, flow rate, and wind speed ； Then, let’s try the SIL grading with the previous SIS system – is that appropriate? I need to be on-site; with such a set of components, I’m afraid I’ll again think there’s something wrong with the design. Currently, some domestic standards are being revised gradually. For example, the standards for blast-resistant control rooms no longer simply specify a certain value for the shock wave load; instead, the shock waves are calculated based on the substances that may leak. Although this approach is not yet fully developed, it does reduce the reliance on arbitrary assumptions and makes the standards more reasonable.
The nitric acid purchased externally has a maximum concentration of 58% upon arrival; during use, acids with concentrations of 18% and 8% are produced as by-products. In the production process, these acids with concentrations of 18%, 8%, and 58% are mixed together, and the actual concentration used is around 30%； Strictly speaking, 200t would constitute a major hazard source, which seems a bit inappropriate; this issue needs to be consulted with local experts. It’s fine to adopt strict standards in design, but having a bunch of nitric acid tanks at 8% concentration and applying all the requirements from AQ3036 to them is rather odd!
2015 Catalog description: Oxidizing liquids, Category 3; Skin corrosion/irritation, Category 1A; Severe eye damage/eye irritation, Category 1. However, after checking GB 30000.14, the criterion for identifying oxidizing liquids is as follows: when testing a mixture with a mass ratio of 1:1 between the substance and cellulose, if the average pressure rise time is less than or equal to that of a mixture with a mass ratio of 1:1 between 65% nitric acid solution and cellulose, then it is not considered an oxidizing liquid. I have doubts about what you said – according to the criteria in GB 30000.14, all substances with a nitric acid concentration below 65% are classified as Category 3, which is in line with the 2015 catalog. I don’t understand how it is determined that such substances are not oxidizing liquids. Another issue is that since it involves multiple tanks, there’s no need for “excessive” investment in HAZOP, SIL, or SIS approaches. By carefully examining standard 18218, it’s possible to ensure that these requirements are not met. But ultimately, for this project to be approved, it’s necessary to ensure compliance with local safety regulations; reworking things later can be very troublesome
Talking to people like you is a waste of my time.
According to GB12268un No. 2031, with the exception of nitric acid that produces red smoke, those with a concentration of over 65% are considered oxidizing substances. Section 4.2.3 of standard 18218 deals with the identification of mixtures; those with a concentration of over 65% should be classified as major hazard sources in accordance with Table 2.
Thank you so much! The big problem has been solved! :)