Classification of the fire hazard of xylene
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I recently worked on an evaluation project that involved the material xylene. According to the relevant information (the MSDS for xylene), its flash point is 30°C. According to the relevant regulations, the fire hazard classification of this substance should be Category B; however, Appendix 3 of the Code for Fire Protection Design of Petrochemical Enterprises classifies xylene as Category A B. Please discuss among yourselves how the fire hazard of this substance should be classified
Paragraph 2.0.2 of the Code for Fire Protection Design of Petrochemical Enterprises: II. Liquids of Class B whose operating temperature exceeds their flash point shall be regarded as Class AB liquids. The flash point of xylene is 30 degrees; if the operating temperature for the process being evaluated by the original poster exceeds 30 degrees, it should be considered a Class A B liquid.
To determine Category A, one should consider not only the flash point but also its saturated vapor pressure at 15 degrees Celsius.
Xylene generally exists in three isomers, with relatively large differences in flash point. You need to specify which type it is (ortho, meta, para, mixed?) ), whether to use or store.
According to the chemical dictionary, the molecular weight of xylene is 106.16. Colorless and transparent liquid, with an aromatic odor. There are three isomers: o-Xylene, with a specific gravity of 0.87599 at 25°C/4°C, a freezing point of -25.3°C, a boiling point of 144.4°C, a refractive index of 1.50295, a flash point (closed cup) of 17.4°C, a ignition temperature of 500°C, and a viscosity of 0.75 mPa•s at 25°C ； m-Xylenes has a relative density of 0.8599 at 25°C/4°C, a freezing point of -47.87°C, a boiling point of 139.1°C, a flash point (open cup) of 25°C, and a ignition point of 527.8°C. Refractive index 1.4946 ； p-Xylenes (p=xylenene) have a relative density of 0.8567 at 25°C/4°C, a freezing point of 13.26°C, a boiling point of 138.35°C, and a flash point (closed cup) of 25°C. Its refractive index is 1.49325. Ordinary xylene is a mixed xylene, consisting of o-xylene (10%–15%), m-xylene (45%–70%), p-xylene (15%–25%), and a small amount of ethylbenzene. Its relative density at 20 °C/4 °C is approximately 0.86, and its solubility parameter δ is 8.8–9.0. Soluble in ethanol and ether, insoluble in water. Flammable; its vapors form explosive mixtures with air, with an explosion limit of 1.09%–6.6% (vol). Toxic; its toxicity is lower than that of benzene and toluene, with a maximum allowable concentration in the air of 100 mg/m3. Xylene is divided into petroleum xylene and coking xylene based on its source and production method. Petroleum xylene is obtained by pre-hydrogenation refining, catalytic reforming, and separation of light petroleum fractions ； Coked xylene is obtained from crude benzene through washing and distillation.
I specifically checked Appendix 3 of the \"Code for Fire Protection Design of Petrochemical Enterprises\", and both m-xylene, o-xylene, and p-xylene are classified as Class A B substances
MSDS documents collected from the Internet are often not reliable; to determine the fire hazard category, it is essential to rely on building codes or petrochemical industry standards.
It turns out the original poster didn’t verify the reliability of the information
In Appendix 3 of the \"Code for Fire Protection Design of Petrochemical Enterprises\" GB 50160—92 (1999 edition), which provides examples of the classification of fire hazards for liquefied hydrocarbons and flammable liquids, m-xylene, o-xylene, and p-xylene are all classified as Class A B.
Additionally, it is necessary to consider the lower explosion limit of the mixture of toluene vapor and air; if it is below 10%, it is classified as Category B.
For flammable liquids, if the standards do not specify which category they belong to, we determine their fire hazard category based on their flash point; if the standards already specify it, it is best to follow those specifications
Only GB50160-1992 uses terms such as Class A and Class B; GB50016-2006 only uses terms like Class A, Class B, and Class C. Ordinary enterprises follow GB50016-2006, while petrochemical enterprises follow GB50160-1992. Generally speaking, xylene is classified as Category A
The draft version of the 2008 Code for Fire Protection Design in the Petrochemical Industry does not include any classification system. In the 2006 version, o-xylene was classified as Category A B. According to the 2008 draft: 3.0.2 The fire hazard classification of liquefied hydrocarbons and flammable liquids shall be carried out in accordance with Table 3.0.2, and the following provisions shall be met: 1. Liquids of Category B with an operating temperature above their flash point shall be regarded as Category A B liquids； 2. Class A C liquids with an operating temperature above their flash point shall be considered as Class A B liquids ； 3. Class C-B liquids with an operating temperature above their flash point should be considered as Class B-B liquids ； Class C-B liquids whose operating temperature exceeds their boiling point shall be considered Class A-B liquids. Table 3.0.2 Classification of fire hazard for liquefied hydrocarbons and flammable liquids. Name Category: Liquefied hydrocarbons – Class A: Hydrocarbon liquids and other similar liquids with a vapor pressure greater than 0.1 MPa at 15°C. Flammable liquids – Class B: Liquids other than those in Class A A, with a flash point ranging from 45°C to 120°C. Based on the above criteria, it should be classified as Class B A; however, if the operating temperature exceeds the liquid’s flash point, it should be considered as Class A B. For example, if the temperature in the storage tank during storage and transportation exceeds the liquid’s flash point, it should be classified as Class A B. The above are merely personal opinions.
There are open-cup and closed-cup flash points; you are referring to the open-cup flash point, which is 30°C, while the closed-cup flash point is 17°C. Therefore, it is correct to classify it as Class A B.
May I ask: Are the flash points specified in stone industry standards and construction industry standards based on the closed-cup flash point? If the closed-cup flash point is used as the standard, should the closed-cup flash point also be included in the safety data sheet for o-xylene? This will make it clearer. Or please ask someone who is an expert in this area to explain it, so that we can learn as well.
All are based on the closed-cup flash point, including building codes and standards. The closed-cup flash point of o-xylene is 17.4°C, so it should be classified as Category A B.
The building code terminology provides an explanation for flash point, and the closed-cup test is used; therefore, I think the closed-cup flash point should be taken as the standard. Open flash point: The value obtained using a specified open flash point tester is called the open flash point, expressed in °C. It is commonly used to determine lubricating oils. Closed-cup flash point: The value obtained using a specified closed-cup flash point tester is called the closed-cup flash point, expressed in °C. It is commonly used to measure kerosene, diesel fuel, transformer oil, etc.
Generally, the flash point of flammable liquids is expressed as the closed-cup flash point. In the ‘List of Hazardous Chemicals’ (2002 edition), is the flash point specified as a closed-cup or open-cup value?
Hello! I would like to ask: What is the fire hazard classification for a 60% calcium nitrate aqueous solution? According to available information, solid calcium nitrate is a strong oxidizing agent; it can catch fire and explode when in contact with organic acids, reducing agents, phosphorus, sulfur, etc. Its classification and coding under hazardous materials regulations are GB5.1 class 51057. Thank you.