grinding Archives

KST, PMAX, MIE… What Does It All Mean for Your Combustible Dust?

by Scott Stearns | Aug 22, 2018 | Uncategorized

There are many things that can affect the hazard that your combustible dust presents. It’s possible for dust that is very safe under most circumstances to cause a dangerous explosion if something goes wrong. Here we’ll talk about some of the kinds of information that you may need to know about your dust to make sure you are protected.

Many engineers will recommend that you test your dust professionally before finalizing your system design. There are a variety of companies that do this; check with your systems engineer to find out who they prefer to work with. This will require you to send in a sample of your dust. If you have more than one type of dust (for example, fine dust from welding and heavier rough dust from grinding), you will want to send samples of all of them to make sure your system can be designed for maximum safety. Combustible dust explosions kill people every year and cause massive damage to property, and it’s worth controlling the problem safely in your facility.

Dust Test Measurements

PARTICLE SIZE (microns):

Some materials are very inert as large pieces, but will burn rapidly in small particulate. Particle size measurement is usually in microns. This is also important for filter efficiency. Particle size is also very important for health purposes: larger particles may be trapped in the nose and throat where they are easy for the body to get rid of, while fine particles (under 30 microns) travel deep into the lungs.

MINIMUM IGNITION ENERGY (MIE):

This is a measurement of how much energy your dust requires to ignite. 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. MIE is how much energy the dust needs to make it ignite.

MINIMUM EXPLOSIVE CONCENTRATION (MEC):

This measures how much dust must be present to cause an explosion. This measurement is usually with airborne dust. It tells you how much dust in the air will ignite if there is a heat source around. This is important because it explains how much dust needs to be floating around in the air to cause an explosion. A secondary explosion, which happens when dust that accumulates in the area lofts into the air by the first explosion, can involve a lot more dust and be a lot more dangerous.

MINIMUM AND MAXIMUM EXPLOSION PRESSURE (P_MINand P_MAX):

The minimum and maximum explosion pressure. Personnel conduct tests on dust inside a container that can measure pressure. P_minis the smallest amount of pressure that ignition of the dust can produce. Then there’s P_max, which is more important. It is the maximum amount of pressure that explosive ignition can produce.

P_maxis 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 is an important calculation because it allows you to calculate how much damage your dust is capable of doing inside a closed container (like ductwork or a dust collector).

MAXIMUM RATE OF PRESSURE RISE/DEFLAGRATION INDEX ( K_ST):

This measurement is done in a similar way to P_max. A mathematical formula converts P_maxto K_ST, taking the volume (size of the chamber) out of the measurement.

K_STis an extremely important test! The P_maxmeasures the maximum pressure that the dust could exert exploding in a closed space, but K_STis a general measurement of explosiveness. It is a standard measurement for dust collection system design purposes.

The Importance of KST

K_ST is a measurement of explosion pressure, NOT of combustibility. A low K_STdoes NOT mean that your dust cannot burn and cause catastrophic damage. K_STonly tells you how strong the potential explosive force, not how flammable the dust is.

A K_STof 0 means that dust is not combustible; its Pmin and Pmax are 0 and in a testing chamber it cannot produce any explosion.

A K_STof greater than 0 means the dust is combustible; testing Pmax can create an explosion in the testing chamber. From 0 to 200 (which includes many metal dusts) the explosion class is 1; a weak explosion. NOTE: a “weak explosion” does not mean “no damage”! The catastrophic Imperial Sugar explosion that destroyed a building and killed over a dozen people was caused by sugar with a K_ST of 1.

A K_STfrom 200 to 300 is a strong explosion (Class 2), and could include things like cellulose dust, other organic fine dust, and some metals and plastics.

A K_STover 300 is a very strong explosion (Class 3). Aluminum and magnesium dust are in this category.

Any dust with any K_stabove zero is potentially combustible and can cause an explosion. Your 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 vent panels are also critical to make sure that an explosion does not cause serious damage if it does occur.

Dust Testing: Putting the Pieces Together

As you can see, all of these pieces of information are important when testing your dust.

– The K_ST(which is calculated from P_Max) tells you how strong an explosion is likely to be.

– The size of the dust is important in determining whether it is combustible.

– The MIE tells you how much or how little energy it will take to ignite your dust

– The MEC tells you how much dust in the air will risk an explosion

A dust with a low K_ST(sugar, as an example, but also many metals) has a low but not zero K_ST. It is not going to cause a strong explosion. However, in one facility that had a lot of accumulated sugar dust, an overheating piece of equipment exceeded the dust’s MIE value and ignited it. With so much sugar in the air, the MEC was also exceeded and the dust in the air ignited explosively.

To review: in this instance, a dust with a LOW K_ST(sugar) was in contact with a heat source that exceeded the MIE and ignited the dust. Because there was a large amount of dust in the air, the MEC was too high and the dust exploded. Secondary explosions caused even more damage because the explosions blew dust into the air and raised the MEC even more. For more information on this incident, see the Chemical Safety Board’s report of the Imperial Sugar Explosions.

While this explosion did not have a high pressure, it did create multiple large low-pressure explosions that blew apart the building and caused numerous deaths. A low K_STdoes not mean your facility is safe from combustible dust explosions.

Table 1: Key Terms and Definitions

OSHA on Combustible Dust

Article featured in the July/August Issue of Shop Floor Lasers. Go here to see the digital issue. SHOP FLOOR LASERS

Read our white paper on combustible dust.

Creative Pultrusions – Fiber Reinforced Plastic (FRP)

by Scott Stearns | Aug 9, 2018 | Uncategorized

Creative Pultrusions manufactures fiber reinforced plastic for the infrastructure, marine, and other corrosion-resistant markets. Fiber reinforced plastic is durable, resistant to corrosion and damage over time, and makes an excellent support material for many projects.

The company not only manufactures large pieces of fiber reinforced plastic, but they also do many kinds of secondary work, including drilling, sanding, cutting, and CNC machining, which produce large amounts of dust. Testing identified this dust as weakly combustible.

When Creative Pultrusions ran into OSHA’s increased interest in combustible dust management, they considered upgrading their current system of vacuums and slide gates, but discovered that a new system from Imperial Systems was just as cost-effective as trying to rebuilt the old one.

Working with Creative Pultrusions, Imperial Systems was able to design for them a turnkey CMAXX Dust & Fume Collection system that met all of their needs. Once main concerns was air flow to the very large CNC machines that the company uses on large pieces of material. With specially engineered and placed fans, the CNC machines got all the airflow they needed, and the rest of the facility got the dust protection that it needed.

In a large facility where there are so many different stations for grinding, sanding, drilling, and machining, there are many locations for dust to be produced. Imperial Systems was able to design a system where dust was safely captured at all of these check points and removed from the work area.

One important aspect of the system designed by Imperial Systems was the complete fire and explosion prevention equipment that helped them meet NFPA standards on combustible dust. The system even allowed them to increase safety and dust control in areas that hadn’t had sufficient dust collection before the new system.

The company feels safer from combustible dust risks, and they feel confident that they are meeting all NFPA standards and they are prepared for any of OSHA’s expectations. Because Imperial Systems products are built to last, the company remains just as happy with their system today as they were the day it was installed, and confident that they made the right decision in choosing to go with Imperial Systems.

At the time, as a company still building our reputation in the dust collection field, the opportunity to work with a local Pennsylvania company to showcase our skills was a great chance to prove everything we are capable of, and the system we designed was, and continues to be, a showcase of the quality of work that we provide to our customers every day.

We continue to provide as-needed maintenance and support to Creative Pultrusions as their needs grow and adapt. Customer service is a hallmark of Imperial Systems and our field service teams are second to none in their level of expertise and skills.

If you are looking for a new dust collection system, please take a few minutes to watch the video and hear the people from Creative Pultrusions describe in their own words how this system has changed their facility and provided them with exactly what they were looking for.

Hot Work and Your Dust Collector

by Imperial Systems | May 16, 2018 | Uncategorized

Sometimes it’s necessary to cut or weld, or hot work in the vicinity of your dust collector. However, this can be extremely dangerous if your dust is explosive. A dust collector, after all, is an accumulation of dust. If that material is combustible, careless hot work could lead to a catastrophic explosion.

“Hot work” is defined by OSHA as “welding, brazing, cutting, soldering, thawing pipes, using heat guns, torch applied roofing and chipping operations, or the use of spark-producing power tools, such as drilling or grinding”. Most of us would think twice about welding or cutting in near a dust collector or any other combustible dust. But some tools, even ones that shouldn’t produce sparks, may have faulty wiring. This can lead to a fire or explosion.

Hot Work Procedures

No hot work should be done near the dust collector without the correct procedures (see NFPA 51B). This NFPA standard specifically defines the procedures for conducting this type of work anywhere that it might cause an explosion.

Hot work near or on a dust collector might include repairs or adding/removing a piece of equipment or ductwork. It may include any number of other projects. Before doing this kind of work around the dust collector, you must have a hot work procedure IN WRITING:

Shall be in writing and available to anyone conducting hot work in the area
It must require an inspection of the work area before the work starts
Must have a permit signed to show that all phases of the work have been inspected and approved

The program should assess safety equipment in the area. On a dust collector that might include a spark arrestor, spark detector, fire suppression or sprinkler system, abort gate, explosion venting, or other types of fire and explosion safety devices.

Hot work may require completely blocking the ductwork to the dust collector, or if the work is on or close to the collector, may require removing the filters, emptying or removing the hoppers, and thoroughly cleaning the entire dirty air side of the dust collector. a strong g recommendation is that a fire suppression system is in place before hot work begins. This will suppress any fire that might start. Further, remove as much of the dust as possible if it is explosively combustible.

Permits Ensure Safety

NFPA 51B specifies that the company safety specialist will issue a permit for work to proceed once achieving an inspection and determination of safety for hot work. It’s the job of this designated safety specialist to inspect the area of hazards. The specialist ensures the removal of all combustible dust. They confirm the isolation of all sparks and heat and establish safety procedures in the event of a fire.

No one should be allowed to perform ANY type of hot work, including the use of spark-producing power tools, in the vicinity of the dust collector without a permit. However, it happens all the time and puts lives at risk if the dust is combustible. Take the time to assess this hazard in your own workplace. If the hazard exists, your safety professional should set up hot work procedures to make sure no one puts themselves or the facility at risk.