Many things can affect the hazard that combustible dust presents. So it’s important to understand the potential. For example, it’s possible for a dust that is very safe under most circumstances to cause a dangerous explosion if something goes wrong.
Combustible dust explosions kill people every year and cause massive damage to properties. Therefore, it’s worth understanding the potential dangers to better protect your employees, especially when you are investing in a dust and fume containment system.
To avoid dangerous situations, it’s recommend that you have your facility’s dust professionally tested before finalizing any dust collection system design. Fortunately, a variety of companies offer this service, but it’s good to first check with your systems engineer to find out which companies they prefer to work with.
Once you get the green light, you need to send in a sample of dust. If you have more than one type (fine dust from welding and heavier, rough dust from grinding), send samples of all of them to make sure your dust collection system can be designed for maximum safety.
The CMaxx dust and fume collection system underwent explosion testing, proving the system can be used as a flame front deflagration arrester when used in conjunction with IDA DeltaMaxx filters.
Dust testing measurements
1. Particle size (measured in microns): Some materials are very inert as large pieces, but will burn rapidly as small particulate. This is important to know in regard to filter efficiency. Particle size is also related to employee health risks. Larger particles can be trapped in the nose and throat where they are easy for the body to get rid of while fine particles (under 30 microns) can travel deep into the lungs where they can cause short- and long-term damage.
2. Minimum ignition energy (MIE): This is a measurement of how much energy is required to ignite the dust. Some dust requires a lot of energy to ignite (in some explosions, the source of ignition has been an overheating bearing or an open flame). Other dust can ignite with much less energy. Static charges can ignite many types of dust.
3. Minimum explosive concentration (MEC): This is a measurement of how much dust must be present to cause an explosion. It is usually measured with airborne dust and tells you how much dust in the air will ignite if there is a heat source present. This is important because it explains how much dust needs to be floating in the air to cause an explosion. A secondary explosion, which happens when dust accumulates in an area is lofted into the air by a first explosion, can involve a lot more dust and be a lot more dangerous.
4. Minimum and maximum explosion pressure (Pmin and Pmax): Tests are conducted inside a container to measure the minimum and maximum explosion pressure of dust. Pmin is the smallest amount of pressure that an ignition of dust can produce where, logically, Pmax is the maximum amount of pressure that an ignition of dust can produce.
Pmax is measured by increasing the concentration of dust inside the closed chamber and measuring the pressure of the explosion until the maximum is reached (until the greatest possible amount of damage has been determined). This measurement allows you to calculate how much damage the dust is capable of doing inside a closed container, such as inside ductwork or a dust collector.
5. Maximum rate of pressure rise/deflagration index (KST): KST is widely accepted as a standard measurement for dust collection system design. While Pmax measures the maximum pressure the dust could exert exploding in a closed space, KST is a general measurement of explosiveness. It’s determined in a similar way to Pmax where a mathematical formula is used to convert Pmax to KST taking the volume (size of the chamber) out of the measurement.
The importance of KST
It’s important to understand that KST is the measurement of explosion pressure, not of combustibility. Another way to put it is that a low KST does not mean that the dust cannot burn and cause catastrophic damage. It only indicates how strong the potential explosive force is, not how flammable the dust is. Put into context:
- A KST of 0 means that the dust is not combustible; its Pmin and Pmax are 0 and in a testing chamber cannot produce any explosion.
- A KST greater than 0 means the dust is combustible; when Pmax is tested, it can create an explosion in the testing chamber. From 0 to 200 (which includes many metal dusts), the explosion is weak (Class 1). A “weak explosion,” however, does not mean “no damage.”
- A KST from 200 to 300 creates a strong explosion (Class 2), and includes things like cellulose dust, other organic fine dust, and some metals and plastics.
- A KST greater than 300 is a very strong explosion (Class 3). Aluminum and magnesium dust are in this category.
Any dust with a KST greater than zero is potentially combustible and can cause an explosion, meaning the dust collection system will require appropriate fire and explosion prevention. Fire prevention is key to keep ignition sources out of the dust collector, including spark traps, abort gates, and water or chemical suppression systems. Explosion venting is also critical to make sure that an explosion does not cause serious damage if it does occur.
