In the coatings, inks and chemicals industry, flash point is a key safety technical parameter. It does not describe the end-use performance of a product, but quantifies the potential fire hazard of a material during production, storage, transportation and use. The accurate understanding and measurement of this parameter is the scientific basis for industry safety management.
1. Definitions of terms
Flash point, also known as flash point, is defined as the minimum temperature at which instantaneous flash (flash) can occur when the mixture formed by vapor and air formed on the surface of a flammable liquid comes into contact with the test flame under specified test conditions. This phenomenon is characterized by the fact that flames appear instantaneously and then go out, rather than burning continuously.
To understand flashpoint, we need to distinguish between two closely related but different concepts -
Flashpoint- The lowest temperature at which instantaneous flashing occurs.
Ignition point(or ignition point) - the minimum temperature at which liquid vapor can be ignited and burned continuously (generally not less than 5 seconds) on the basis of the flash point. Typically, the ignition point is several degrees Celsius higher than the flash point.
| Comparison of core concepts | |
| Flashpoint | The minimum temperature at which instantaneous flashing occurs is the core basis of safety classification-5. |
| Ignition point | The minimum temperature at which continuous combustion occurs is not used as a conventional hazard classification index-5. |
In addition, according to different test instruments, flash point data can be divided into closed cup flash point and open cup flash point, which have clear numerical differences and different uses.
2. Standardized measurement methods, instruments and key standards
The value of flash point is not an absolute constant of matter, and its measurement results are closely related to the standard method and type of instrument used. Therefore, testing against uniform standards is a prerequisite for data comparability.
1. Core test methods - closed cup method and open cup method
The main test methods are divided into closed cup method and open cup method, and the fundamental difference is whether the sample cup is open during the test process.
Closed cup method - the test is carried out in a closed cup, and the sample vapor is not easily lost. This method simulates the safety conditions of confined or confined spaces (e.g., inside storage tanks and drums), so the measured closed cup flash point value is relatively low, which can more closely reflect potential risks. Closed-cup flash point data is used as a basis in international chemical classifications (e.g., GHS systems) and transportation regulations.
Open cup method – the test is performed in an open cup and the sample vapor can diffuse freely. This method simulates an open container or open environment, and the measured flash point of the open cup is usually 4 to 5 degrees Celsius higher than the flash point of the closed cup. It is more suitable for evaluating safety when machining or using in open environments.
2. Instrument types and standard evolution
Corresponding to different methods, flash point analyzers are mainly divided into closed-cup flash point meters and open-cup flash point meters. Modern instruments generally adopt automatic control, integrate heating, ignition, detection and cooling functions, and have the ability to automatically correct atmospheric pressure to improve test accuracy and efficiency.
The standards are constantly updated. For example, the newly released national standard GB/T 21790-2025 is equivalent to the international standard ISO 3679:2022, which was implemented in February 2026, replacing the 2008 version. This standard adopts a small closed-cup tester, which is suitable for a variety of products such as coatings, adhesives, solvents, etc., and represents the development direction of rapid and accurate testing.
3. Method selection and influencing factors
The method selection was mainly based on the volatility of the sample and the expected flash point range. In the test, the uniformity of the sample, the starting temperature, the heating rate, the type and frequency of the ignition source will affect the accuracy of the results. Samples containing halogenated hydrocarbons or water may require special handling.
3. Key factors affecting flash point
The level of flash point is essentially a combination of liquid volatility and flammability after vapor mixing with air. The main influencing factors include-
The volatility of matter itself - this is the main internal cause. The lighter the fraction and the smaller the molecular weight, the easier it is to evaporate, so that the combustible vapor concentration is reached faster above the liquid level, so the flash point is lower.
Composition of the mixture – For complex formulations such as coatings and inks, the flash point is primarily determined by the most volatile solvent component in the formulation. Adding high boiling point solvents is an effective means to improve the flash point of the product. Conversely, if a product is accidentally mixed with low-flash point impurities (such as fuel oil mixed with lubricating oil), it will result in a significant drop in flash point, which is an important signal for contamination or quality incidents.
External conditions - an increase in air pressure above the liquid surface will increase the flash point. Therefore, standard test methods require atmospheric pressure correction of the results.
4. Specific applications in coatings, inks and related industries
In the field of coatings and inks, flash point measurement has clear application scenarios and values.
Product safety classification and labeling – Based on closed cup flash point data, it is possible to determine whether a product falls under the category of "flammable liquid" and its hazardous category. For example, liquids with a flash point below 23 degrees Celsius are generally considered highly flammable, which is directly related to the safety labeling of the product, the preparation of safety data sheets and the fire protection rating of the warehouse.
Transportation compliance determination - domestic and foreign land, sea and air dangerous goods regulations use flash point as one of the core indicators to divide packaging categories and transportation conditions. Products must pass compliance testing to meet shipping requirements.
Production process and storage safety – Understanding the flash point of raw materials and products is the basis for setting safe production temperatures, designing ventilation systems, and developing fire prevention and control measures. For example, when operating in an open vessel, the heating temperature is usually controlled within 10 degrees Celsius below the flash point.
Product quality control and R&D – Flash point is an indicator that monitors the consistency of a product's formulation. When developing new environmentally friendly or high-performance products, such as high flash point coatings, formulation adjustments, such as the selection of specific solvents and additives, are required to meet higher safety standards while meeting performance.
Summary
All in all, flash point is a practical parameter that closely integrates basic chemical principles with industrial safety management. It converts the fire hazard of liquids into measurable, classifiable, and manageable specific temperature data through standardized instruments and methods. For practitioners in coatings, inks and other industries, mastering the exact meaning of flash point, standard test methods and their impact on product life cycle safety management is an important technical support for compliance operations, risk prevention and control, and product development.