KST value: Fundamentals of dust explosion classification

The KST value is a key classification parameter that describes the explosiveness of a dust-air mixture. Specifically, it represents the maximum pressure rise over time measured during an explosion in a standardized 1 m³ container. This value allows conclusions to be drawn about the dynamics and intensity of a potential dust explosion and thus serves as an essential basis for evaluating and designing protective measures. As a physical quantity, the KST value quantifies the hazard posed by various dusts and forms a crucial foundation for industrial safety assessments.

How is the KST value determined?

The KST value is determined by measuring the maximum pressure rise rate of a dust-air mixture in a standardized 1 m³ container under defined conditions. This is based on the so-called cubic law, which describes the relationship between the pressure rise rate, the volume of the test container, and the KST value:

• (dp/dt)max x V1/3 = const = KSt = Kmax

Determining KST values ​​is of considerable relevance to companies, particularly in connection with the selection and use of extraction systems. This data is essential for the targeted planning and design of dust extraction systems. Only with precise knowledge of the KST values ​​can extraction systems be designed in such a way that not only is the dust concentration effectively reduced, but explosion protection is also ensured through measures such as explosion pressure relief valves, check valves, or inerting.

Dust explosion classes and KST value

The KST value serves as a central measure for classifying the explosiveness of dust-air mixtures . Based on this parameter, dust explosion classes are defined, which allow conclusions to be drawn about the dynamics and hazard of an explosion. The dust explosion classes are divided into three categories:

• Dust explosion class 1 (St 1): KST value > 0–200
• Dust explosion class 2 (St 2): KST value > 200–300
• Dust explosion class 3 (St 3): KST value > 300+

Dust explosion class St 1: Low explosiveness

Dust-air mixtures of class St 1 exhibit a low explosion intensity. The KST value in this range is between 0 and 200, indicating a moderate pressure increase in the event of an explosion. This category often requires only basic protective measures.

Dust explosion class St 2: Medium explosiveness

Class St 2 comprises mixtures with a KST value between over 200 and 300. It exhibits significantly stronger dynamics and requires increased safety precautions due to the considerable pressure development.

Dust explosion class St 3: High explosiveness

Dust-air mixtures with a KST value above 300 belong to class St 3 and are characterized by extreme explosive forces. This category places the highest demands on preventive protective measures and structural safety precautions.

Which materials have high KST values?

Materials with high KST values ​​have a significant explosion potential and require special safety precautions in industrial settings. The following is an overview of substances with high KST values:

• Metal dusts
• Cellulose
• Wood flour
• Polymethyl acrylate (PMA)

Metal dust

Metal dusts such as aluminum, magnesium, and titanium have KST values ​​exceeding 300 bar·m/s and belong to dust explosion class St 3. They cause particularly powerful explosions and pose a significant safety risk in metal processing. Their high reactivity necessitates special protective measures such as explosion pressure relief and inerting.

Cellulose

With KST values ​​between 200 and 300 bar·m/s, cellulose falls into dust explosion class St 2. These organic particles, frequently found in the paper and textile industries, pose a high risk of powerful explosions when stirred up in the air.

Wood flour

Wood flour also has KST values ​​between 200 and 300 bar·m/s and is classified as dust explosion class St 2. The risk is particularly high in joineries and wood processing plants, as the particles are easily dispersed in the air during processing.

Polymethyl acrylate (PMA)

This synthetic polymer has KST values ​​between 200 and 300 bar·m/s and also belongs to dust explosion class St 2. In plastics processing and in the manufacture of acrylic products, it can trigger strong explosions under unfavorable conditions.

What protective measures are required by a high KST value?

A high KST value necessitates specific protective measures to minimize the increased risk of explosion and the associated potential destructive force within companies. These measures can be divided into preventive, constructive, and organizational approaches:

• Avoidance of explosive dust concentrations
• Elimination of ignition sources
• Inerting
• Explosion pressure relief
• Explosion suppression
• Explosion-proof construction
• Regular cleaning
• Employee training
• Maintenance and inspection

Avoidance of explosive dust concentrations

Effective extraction systems, such as dust extraction units, and regular cleaning prevent the accumulation of dust, thereby significantly reducing the risk of explosive mixtures. This preventative measure is particularly important in industrial environments.

Elimination of ignition sources

Potential ignition sources such as open flames, hot surfaces, or sparks must be systematically identified and eliminated. This measure significantly reduces the probability of a dust explosion.

Inerting

Reducing the oxygen content in the ambient air significantly limits the explosive potential. This method is particularly suitable for dusts with extremely high KST values.

Explosion pressure relief

Technical devices such as rupture discs or explosion vents enable the safe reduction of overpressure in order to minimize damage to equipment.

Explosion suppression

Fast-acting detection systems can detect an incipient explosion and automatically initiate extinguishing agents to stop the spread.

Explosion-proof construction

Plant components should be designed to withstand the maximum explosion pressure in order to minimize damage and danger to people.

Regular cleaning

Established cleaning routines effectively remove dust deposits, thus preventing the formation of explosive mixtures.

Employee training

Employees should be made aware of the dangers and instructed in safe working practices and the use of protective measures.

Maintenance and inspection

Regular inspection and maintenance of systems and protective equipment ensure functionality and minimize potential risks.

How do extraction systems help to control KST values?

Dust extraction systems play a crucial role in controlling the effects of KST values ​​and minimizing the risk of explosion in industrial plants. Here are the key approaches:

• Reduction of dust concentration
• Particle size control
• Explosion protection measures
• Zoning and risk minimization

Reduction of dust concentration

Extraction systems remove combustible dust directly at the source, thus preventing the accumulation of explosive concentrations in the air. By reducing the dust concentration below the lower explosive limit (LEL), the risk of explosion is significantly reduced.

Particle size control

Since finer particles generally have higher KST values, they are more explosive. Specially designed extraction systems capture even the finest particles and separate them before they can spread into the surrounding area.

Explosion protection measures

Most dust extraction systems are often equipped with devices such as explosion pressure relief valves, flameless pressure relief valves, and non-return valves. These protective systems are individually designed to meet the specific KST values ​​of the dust being extracted in order to ensure safety.

Zoning and risk minimization

Targeted extraction allows for the containment of explosion-hazardous areas and their classification according to ATEX standards. This zone classification facilitates the implementation of specific protective measures in particularly hazardous areas.

Kaweha extraction technology

Rely on innovative extraction technology from Kaweha to effectively control explosion risks in your company. With our extraction systems, such as the Dustmaster, and individually designed systems, we meet the highest ATEX guidelines and reduce dangerous KST levels directly at the source.

From planning and consultation to installation and employee training – we provide the right solutions for your industrial dust extraction needs. Secure state-of-the-art explosion protection and ensure optimal safety in your company. Contact us for a customized quote.