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Dust and Fume Collection: Do you need it?

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Dust and Fume Collection: Do you need it?

DUST AND FUME COLLECTION:  SOME INDUSTRIES THAT MIGHT NOT KNOW THEY NEED IT

Dust and fume collection in a manufacturing facility is important for many reasons.  Here are the top five reasons you should consider:

 

Top 5 reasons you need dust and fume collection

NOT CONVINCED YET?

Can you name the metal that causes cancer, damages skin, eyes, lungs, and kidneys, and is found in everything from stainless steel to dyes and pigments?

 

If you said this compound is HEXAVALENT CHROMIUM (https://www.osha.gov/SLTC/hexavalentchromium/) you’re right.

 

Chromium is a component of stainless steel, added to make the steel more corrosion-resistant. The fumes produced from welding, laser cutting, or plasma cutting stainless steel contain hexavalent chromium. While this form of chromium is known to cause cancer, it also directly attacks the lungs and kidneys and can cause severe eye and skin irritation.

Hexavalent chromium doesn’t just appear in welded or heated stainless steel. Electroplating with chrome also presents a hazard, and hexavalent chromium compounds are used as pigments in inks, paints, and many types of plastic. Working on any material plated with chrome or coated with a chromium-containing material may release hexavalent chromium into the air.

Think hexavalent chromium isn’t something to worry about in your type of business? You may need to reconsider. OSHA TESTING (OSHA TESTING: https://www.osha.gov/SLTC/hexavalentchromium/) showed which types of facilities had detectable levels of this dangerous metal in their air. The following are some of the top offenders:

  • Nonresidential building
  • Highway, street, and bridge
  • Foundation and structural materials
  • Foundries
  • Forging and stamping
  • Architectural and structural metals
  • Boiler, tank, and container
  • Coating
  • Engraving
  • Heat-treating
  • Agricultural machinery
  • Mining machinery
  • Ventilation and air-conditioning
  • Aerospace products and parts
  • Ship and boat building
  • Automotive repair and maintenance

Any surprises on this list? If your facility is part of any of these industries, contact us at 800-918-3013 for an assessment of your dust and fume collection needs.

 

Dust Explosions: The Hidden Hazard

Dust explosions are bad to begin with, but what do you know about secondary explosions?  There are many factors that determine how likely a particular type of dust causes a deflagration. When you think of combustible dust, do you think of the explosions you’ve heard about at grain handling facilities? Maybe you think of the explosive potential of aluminum dust.

 

Three dust explosions that occurred in 2003 demonstrate how many different types of production and manufacturing can produce a deflagration risk (http://www.fireworld.com/Archives/tabid/93/articleType/ArticleView/articleId/86899/DEADLY-DUST.aspx). In a North Carolina plant, the accumulated dust came from a polyethylene coating being applied to rubber. As the material dried, dust was formed and accumulated above the work area. Even though the work area itself was very clean, a layer of dust a quarter of an inch thick was enough to cause an explosion that killed six people. In this situation, a dust collection system in the production area could have captured the dust particles as they came off the material, before they were allowed to circulate through the facility.

dust explosions

The explosion in Kentucky was caused by combustible dust that resulted from a resin used to treat fiberglass. Workers were aware of the large quantities of dust, but cleaning processes often just caused more of the dust to become airborne, and it accumulated in the ductwork and in dust collection equipment. There were no safeguards in place to prevent a flame front from traveling through the ductwork or getting into the dust collector. An abort gate with spark or flame detection could have identified and stopped the fire from spreading, and dust collectors designed to stop deflagration fronts could have prevented the dust collectors from becoming sites of secondary explosions.

 

The explosion in Indiana was fueled by aluminum dust from scrap processing. The dust collector in this case was the source of the explosion. It did not have explosion venting, and instead of being directed safely, the explosion traveled back into the building and ignited dust in the ductwork. A secondary explosion occurred when dust accumulated on surfaces inside the facility ignited. A dust collector designed to isolate and redirect a deflagration could have prevented this accident.

 

The National Fire Protection Association, which establishes many of the codes and standards for handling potential fire hazards (http://www.nfpa.org/codes-and-standards/all-codes-and-standards/list-of-codes-and-standards) recommends that all dust collection systems should have explosion venting to redirect explosions and abort gates or other equipment to stop flame fronts from spreading. It also recommends improved housekeeping measures to prevent dust from accumulating, which may be accomplished by collecting dust at the source so it cannot accumulate in difficult-to-reach places.

 

It’s often this accumulated dust, hidden on high surfaces, in corners, or inside ductwork, that ignites to cause a secondary explosion that’s far more dangerous than the original one. Witness reports of dust explosions often include descriptions of a smaller explosion followed by one or more larger ones; this is secondary ignition (https://www.osha.gov/Publications/osha3791.pdf). Dust control throughout the entire facility, along with fire prevention equipment such as abort gates, spark arrestors, and explosion venting, can control a potential explosion and prevent a small fire from becoming a fatal disaster.

The Air You Breathe At Work: Ask Questions

ASKING QUESTIONS ABOUT THE AIR YOU BREATHE AT WORK

OSHA rules mandate that you have a right to know about any safety hazards that are present in your workplace, including the air you breathe. Most managers, supervisors, and owners want their employees to be safe and want to avoid putting their employees in danger. But there may be workplace hazards they don’t know about, and sometimes an employee’s questions can help them become aware of a situation.

 

For managers, supervisors, and other bosses, an employee concern about a safety issue is a chance for you to work on resolving the problem as a team. The biggest OSHA fines go to employers who ignore safety issues. Employers who are working in good faith to resolve safety issues may receive recommendations from OSHA, but the gigantic fines are usually reserved for employers who have shown that they don’t care about fixing safety issues.

 

The best way to avoid safety issues in your workplace is for employees and bosses to communicate about any concerns in a cooperative way. This benefits everyone, and an employer who listens to and works to resolve the concerns of their workers will find that a reputation for being proactive and concerned about employee safety is good for business.

 

Since industrial dust and fume control is our business, making sure that workers are breathing clean, safe air is the aspect of safety we’re most concerned with. Many workplaces don’t know they need a dust or fume collector, or don’t know when their collector isn’t working efficiently. If employees are concerned about what they might be breathing or exposed to in the air, a good employer should listen to those concerns and find answers for them.

 

Workers can be proactive in protecting their health by learning some important information about the materials they work with and what risks they might involve. For example, workers who are involved in cutting, welding, or otherwise producing fumes from stainless steel should have some awareness of hexavalent chromium. Workers who manufacture plastic products may need to be made aware of toxic elements like cadmium that may be used as stabilizers as well as hazards from the plastic itself. If you’re uncertain what hazards might be in the air in your workplace, you have a right to ask for more information about the air you breathe. This information should always be available to you.

 

If employees have questions, OSHA has many options for safety training and awareness. An employer may be able to make concerned workers feel empowered and more knowledgeable by answering their questions and making sure they get the training they need. Employers are obligated to provide their employees with information about any hazards in their workplace, but sometimes those hazards may not be recognized until an employee asks a question.

 

If you’re not sure what’s in the air you breathe in your workplace, you have a right to ask your employer about it. As an employer, it’s your job to check out your employee’s concern and determine whether there is a health hazard that needs to be addressed. Proactively dealing with an employee’s concern shows respect for their needs and also a meaningful interest in employee safety and health.

 

If you feel that there’s a health risk in your workplace that you need to talk to your supervisor or employer about, you should know that OSHA regulations protect you from being punished or from any kind of retaliation, and your employer probably knows this.

 

The discussion will be more productive if a few points are kept in mind:

  • The discussion is not an accusation. It is a question or issue that you would like more information about or are concerned about.
  • The focus should be on making sure you and your coworkers are healthy and safe, because this is good for everyone and for the company.
  • You have a right to ask for more information, more training, better protective equipment, or whatever you feel like you need to be safer. Being specific about how the problem could be solved helps people move forward with solutions.
  • Be specific about your concerns and ask questions. If you feel like you don’t have enough information, talk to someone who can help you find what you need or look up some general information on the topic.
  • Approach the discussion with the attitude that you and your employer have a mutual problem that you can work together to solve.

 

An example of how you might start a positive conversation:

1) I have a question about the welding fumes in the shop. It seems like some of the stations have a lot of fumes around them sometimes. Is there something we could do about that?

Or:

2) Some of us noticed that even though we do a lot of sweeping and cleaning up, there’s dust getting stuck up in places where we can’t reach it. What’s the safest way for us to deal with that?

Or:

3) I noticed there’s a sign up about (safety hazard), but I’m not sure we all know as much about it as we should. Is that something we could get some more information about?

 

Good ways for a supervisor or employer to respond to these might be:

1) We can definitely look at those stations and see if something needs to be done about the welding fumes. Are there places in the shop that are the biggest problem?

Or:

2) That’s a good question. We’ll have to figure it out. Does anybody out in the plant have any ideas for how to handle it?

Or:

3) Let me check out the OSHA website and see what they’ve got. I want to make sure you have all the information you need.

 

Of course, these things only matter if you follow up. Ignoring an employee’s safety concerns isn’t just disrespectful. It’s also a violation of OSHA regulations. And employees who aren’t comfortable talking to their supervisors about safety issues always have the right to contact OSHA for assistance. An employer who retaliates against, punishes, or fires an employee for reporting a safety concern to OSHA can face lawsuits and very large fines. Keeping the lines of communication open benefits everyone if a company can work as a team to identify and solve safety issues.

Wet Dust Collector Vs. Dry?

Since we manufacture dust control systems that use filters (bags or cartridges) to collect and control dust, we obviously have a preference for dry systems.  But what about a wet dust collector? Both wet and dry systems have their advantages and disadvantages. Many of them depend on your process, the type of dust you produce, and your individual needs. Baghouse and cartridge filter dust collectors have worked safely and efficiently for many years and in many different applications.  However, as concern and awareness of combustible dust issues grows, some companies are considering a wet system that “scrubs” the air stream with water for dust control. Read on for some points to think about:

 

THINGS TO CONSIDER:

  • Type of dust

Wet dust collector systems are often used where there is a concern about combustible dust, especially metal dust, combined with a high likelihood of sparks coming into contact with the dust. Dry systems can also be used in this application.  Although, if there is a risk of deflagration, the system should include safety devices such as spark traps, and fire-retardant filters that will not fuel a fire. Our DeltaMAXXTM nanofiber fire-retardant filters are rated to safely control a deflagration inside the collector. Wet systems decrease the risk of fire or explosion because the air travelling through the collector is cleaned by “scrubbing” it with water before allowing the dust to settle out. This ensures that even if there is an ignition source, there’s no dust cloud or dry dust to ignite. On the other hand, dry collectors with proper maintenance and housekeeping have been used safely for many years with almost every type of dust imaginable.

 

  • Particulate Size

The filters in dry systems are more efficient at collecting and removing very fine particulate, with nanofiber filters 99.9% efficient in capturing particulate down to .3 microns. While some cutting and grinding may produce larger particulate, applications like welding, plasma and laser cutting, and other processes produce very fine particulate metal fumes that are more efficiently captured by a dry collector system. In a wet system, it may be difficult to get very small particulate to settle out of the water so it can be collected, although some wet systems are designed to handle this. Overall, a dry collector is more efficient for smaller particulate, smoke, and welding fumes.

 

  • System Setup

A wet dust collector is often used on individual work stations such as downdraft tables. When a central dust collection system is used, the requirements for ductwork and proper CFM throughout the system may be similar for wet and dry types. Because a dry system is more efficient at capturing smaller particles and fumes, these types of systems are often used where there are multiple locations in a facility producing welding or cutting fumes. Since dry systems are more effective in collecting smoke and fumes, they may be able to operate at a lower CFM, which saves energy and decreases the noise produced by the system. A wet collector is often used on equipment like a downdraft table where sparks and metal dust are in close proximity, although many downdraft tables use a dry collector because they produce small particulate, smoke, or fumes. A full assessment of your company’s needs will help determine which type of system would be most beneficial for you both for safety purposes and in long-term operating and maintenance costs.

 

  • Maintenance and Disposal

Depending on your type of dust, there may be regulations for how your material needs to be disposed of. With a dry system, bags or cartridge filters usually filter the dust into a container for disposal. With a wet system, the accumulated dust settles out of the water and the sludge must be collected and disposed of. Since the sludge will eventually dry, it is often mixed with an inert substance like sand to make it safer to handle. Many waste management facilities have different regulations for dry and wet materials.

 

To make a wet collector efficient at removing smaller particles, the system requires higher water pressure and a lot of energy, which increases the cost. For larger particles, the energy costs are lower because it is easier to get these particles to drop out the air stream. A dry collector requires compressed air to periodically clean the filters, and the frequency of pulsing can be adjusted to suit individual needs, and can be decreased by the use of filter media like DeltaMAXX nanofiber that pulse-clean more efficiently. Both types of systems require appropriate equipment to maintain the correct air flow.

 

Maintaining a dry dust control system usually means changing the filters regularly and monitoring differential pressure. The filters will contain dust and must to be disposed of according to the standards for that material, and the collected dust must also be disposed.  Maintaining a wet dust collector system includes making sure the water remains clean, without too much material dissolved in it, and disposing of contaminated wastewater. Removal and disposal of sludge is required for a wet collector, and the sludge may need to be mixed with other materials or dried to make it safer or more easily disposable. Both types of systems will require proper housekeeping and maintenance of the ductwork and work areas to make sure dust doesn’t accumulate.

Contact the professional staff at Imperial Systems today to learn more about solutions to your dust control concerns.  800-918-3013.

Combustible Dust Standard: A Stalemate

STALEMATE BETWEEN FEDERAL AGENCIES MAY BE MOVING TOWARD RESOLUTION

A combustible dust standard may mean more stringent control measures, a lot of new tests and reports, and major growth in the air quality control industry, especially dust collection systems.

Since 2008, the National Fire Protection Association (NFPA) and the U.S. Chemical Safety Board (CSB) have been making recommendations to OSHA that a formal standard for combustible dust is needed to prevent worker injuries and deaths caused by dust explosions. OSHA established a “National Emphasis Program” to provide more information and awareness about dust control and combustible dust hazards. They have yet to establish any formal, enforceable standards. The CSB continues to make recommendations for such a standard in their investigations of explosions and resulting fatalities (http://www.csb.gov/us-chemical-safety-board-determines-osha-response-to-seven-open-csb-recommendations-on-dust-fuel-gas-and-process-safety-management-to-be-unacceptable/) and has deemed OSHA’s response to their recommendations to be “unacceptable”. They consider an OSHA combustible dust standard to be the most important safety measure they have recommended.

According to John S. Forester, the managing editor at Powder & Bulk Solids, (http://www.powderbulksolids.com/) the NFPA is currently working on revisions of its standard 652, its proposed standard for combustible dust, intended to be comprehensive and to cover all industries to which it would apply.

This combustible dust standard (https://www.nfpa.org/Assets/files/AboutTheCodes/652/652_PreliminaryDraft.pdf) would require that all facilities, new or existing, complete Dust Hazard Analysis testing and report their results. Also, some of the standards will be applied retroactively to existing businesses. In response, OSHA seems to be responding to the call for increased regulation for the first time since 2010. However, there’s no sign of new enforceable regulations in the immediate future. Facilities who need to meet NFPA standards may find themselves dealing with the mandated Dust Hazard Analysis. This will mean an increased investment in dust control systems.

The article notes that due to increasing regulation and the adoption of NFPA standards globally, the market for industrial dust collectors is expected to increase significantly in the following years. Demands for explosion isolation equipment (such as Imperial Systems independently tested, NFPA-standard CMAXX with In-Line Deflagration Arrester filters) are expected to be even higher as reports of industrial accidents and stricter regulations circulate in the industry.

The NFPA 652 will require industry-wide testing of all dusts that might be combustible and full analysis of all facilities for areas and equipment that might create a risk of dust accumulation, such as conveyor belts, elevators, ductwork, and ovens. Dust testing may include standards on the amount of dust allowed to accumulate on any surface and testing to determine whether the dust is in contact with hot surfaces or static buildup that could trigger ignition of that particular dust. These assessments will be an ongoing headache for many companies, and installing a system of correctly functioning dust collection equipment (and maintaining it or having it maintained by our ServiceMAXX professionals) can minimize that headache by keeping the dust problem minimal and keeping the facility up to standards.

While the expected boom in sales of industrial dust extraction and explosion suppression equipment is good news for our industry, it’s especially good news for Imperial Systems, since our CMAXX with IDA filters already meets NFPA standards and should continue to meet the new standards in the future. If you already have one of our systems and it is well-maintained and operating properly, you should be prepared to weather any new regulations for explosion-containing dust collection systems. If you’re using another type of dust collector, measures such as high-speed abort gates and our fire-retardant DeltaMAXX nanofiber filters can help you be in compliance with current and future standards.

If you have questions about what you need to be prepared, give on of our knowledgeable team members a call today at 800-918-3013!

BagHouses: How They Work

Baghouses and Dust Collectors are often used as synonyms. The baghouse is a system in which air is filtered by bags made of various materials, which are periodically cleaned to remove the accumulated dust. Today, cartridge dust collectors are increasingly popular in many industries, and for good reason: cartridge filters can pack a lot of surface area into a small space and can filter very small (sub-micron) particulate very efficiently. For some industries this is essential, particularly for industries such as metalworking that generate smoke and fumes that contain potentially toxic materials.

The baghouse, however, has been a workhorse industrial dust control for many years, and continues to serve its role today. While the basic concept remains the same, new filter materials and new ways to solve problems make them more adaptable than ever. Not every industry produces dust that’s fine enough to need the high efficiency of a cartridge collector.baghouses

Generally, all baghouses have a tube sheet to which the bags are attached, an inlet for dirty air and an outlet for clean air, and an opening at the bottom for collected dust to drop out. The location of these features depends on the type of baghouse. The main differences between types of baghouses is how the bags are kept clean.

In a shaker baghouse, the bags are cleaned by mechanically shaking them. The bags usually hang from the top of the unit and are attached to the tube sheet at the bottom. In this type of system, air typically enters from the bottom.  It is then pulled through to collect on the inside of the bags. Air then exits at the top as clean air while the dust is collected on the inside of the bags. To clean the bags, the airflow must be shut off and the hanging mechanism shakes the bags to get rid of the dust, which drops out the bottom. These are not the most efficient types of baghouses and can be high-maintenance.  Yes, the design is simple and does not require compressed air or complicated supports for the bags, however damage to the bags can occur from the mechanical shaking mechanism.

In a reverse air baghouse like our BRF, dirty air enters the collector and dust collects on the outside of the bags, which are supported by a metal cage to keep the air pressure from collapsing them. Steady air circulation continuously pulls air through the filter bags. For cleaning, a fan rotates over the bags, blowing reverse air into them to remove dust. This type of reverse air baghouse generates a lower pressure than the compressed air pulses of a pulse jet, which can decrease wear and tear on the bags and save on the cost of compressed air. They are usually very cost-efficient and if used within the parameters for which they were designed, they are very effective.

Also, this type of reverse air baghouse can continue running while cleaning occurs. An older type of baghouse also sometimes referred to as reverse air may collect dust on the inside of the bags and then cut off the inflow of dirty air and use a reverse flow of clean air to partially collapse the bags, which also removes the dust. These types of bags have rigid rings that allow them to flex but not collapse completely, or “pancake”. These types of reverse air baghouses have to be taken off line for cleaning or are divided into compartments so one section at a time can be cleaned.

A pulse jet baghouse is somewhat similar. The bags are supported by metal cages and hang from a tube sheet at the top of the baghouse. Dust and air enter and dust collects on the outside surface of the bags, not the inside. The bags are cleaned by bursts or pulses of compressed air that travel down the length of the bag and dislodge the dust. Because the pulse of air travels very quickly down the bags, this type of baghouse can be cleaned without taking it offline. This allows them to operate more efficiently since dust is removed from the bags at more regular intervals. The downside to these types of collectors is the higher pressure and expense of compressed air, which adds to operating costs.

The EPA provides information (link: https://www3.epa.gov/ttncatc1/dir1/cs6ch1.pdf) to help you make a general calculation of the capital costs of a baghouse dust control system. Their calculations include the cost of the collector, the bags (and cages if necessary), measurement instruments, installation costs, and the annual operating costs (electricity, compressed air, labor, and materials). These costs will obviously vary widely. A pulse jet baghouse requires compressed air, which is not needed for the other types of baghouses, but may require fewer filters since they are more efficient.

One thing that is a major headache for owners of any type of baghouse: replacing the bags. This is usually a dirty, messy, time-consuming job that requires the collector to be off-line for a considerable period of time. It often involves working in an enclosed space. Mechanisms for attaching the bags to the tube sheets vary widely, but especially when cages are involved it can be a very involved process. Some companies installing new dust control equipment choose a cartridge filter collector because vertical collectors like our CMAXXTM are easy to change and do not involve issues with confined spaces. For existing baghouses that need frequent bag changes, a pleated filter bag (link to our page) is an option that should be considered. These have a much larger surface area and last much longer than traditional bags, which means less frequent changes. Also, pleated filter bags do not require cages, which greatly simplifies the changing process.

To learn more about Imperial Systems’ Baghouses, call us today at 800-918-3013.  Our helpful, knowledgeable team members can answer any questions you may have about all types of dust collection solutions.

Toxic Metal Dust Danger

WHAT MAKES GOOD CHROMIUM GO BAD?

HOW THIS ANTI-CORROSION WONDER METAL GETS TURNED INTO AN OCCUPATIONAL HEALTH DISASTER

toxic metal dust danger

Chromium is an amazing metal. It can be polished to a brilliant shine and will keep that shine without tarnishing or corroding. When allowed with other metals, it makes them harder and more corrosion-resistant. Also, electroplating with chromium gives a durable, high-polish coating.

Chromium didn’t get its name by being shiny, though. “Chroma” is the Greek word for “color”, and many chromium compounds come in bright, beautiful colors including purple, yellow, and green. For many years, chrome yellow was used to create the familiar yellow school bus. Chrome pigments that reflect infrared rays are used by the military to conceal vehicles. Chromium salts are used in treated wood and to tan leather.

So what turns this incredibly useful item into a toxic metal dust health hazard?

Metals exist in a variety of oxidation states, depending on the compounds they are part of. Metals are good at sharing electrons, so chromium, like many other metals, can exist in several different oxidation states that are referred to by number. Hexavalent chromium, or chromium (VI) is a chromium compound at the +6 oxidation state. In this form, it mimics other essential elements and tricks cells into taking it in. Depending on the site of exposure, the results can be skin damage, stomach and intestinal injury, or lung damage and eventually lung and kidney cancer.

Many dyes, pigments, and primers contain hexavalent chromium in its direct form. Most exposure, though, occurs when stainless steel or other metals alloyed or coated with chromium are heated by welding, grinding, or cutting. The heat involved in these processes causes previously stable and harmless chromium to oxidize to its dangerous hexavalent form.

Welding fumes, grinding or metalworking dust, and fumes from plasma or laser cutting tables can all contain this form of chromium. So can dust or smoke from treated wood, dust left over from leather tanning, and residues from electroplating with chrome or from heat-treating materials with a chromium anti-corrosion coating.

Awareness is the key to prevention

Remember Erin Brockovich?  She made a name for herself fighting a facility in southern California. They had been using hexavalent chromium in its systems as a corrosion prevention agent and then allowed it to contaminate the groundwater. She has since gone on to participate in several other high-profile lawsuits involving the contamination of groundwater with hexavalent chromium in Missouri and Texas.

OSHA and environmental groups including the EPA closely monitor all forms of toxic metal dust including hexavalent chromium. If your facility’s dust collection equipment isn’t up to the job of handling this byproduct, your workers are at risk of health problems.  Which means you could be at risk of fines. Many companies don’t know that their processes are producing hexavalent chromium. This dangerous version of a common and useful metal is found in more types of dust, smoke, and fumes than you may realize.

Dust Testing FYI

THE MECHANICS OF DEFLAGRATION: DUST TESTING RESEARCH

Some dusts are more dangerous than others. The organizations that set standards for combustible dust management, like OSHA and the National Fire Protection Association, run dust testing on many types of dust to determine how dangerous they are and what conditions make them explode.  dust-testing

In many cases, these formal tests replicate what common sense would already tell you. Combustion chambers are often used to measure the amount of pressure that’s produced when a measured amount of a dust is ignited. They are used to measure the minimum concentration of the dust that’s needed to start a deflagration. This is an important number, because even if you don’t normally produce enough dust to reach the concentration that could ignite, a heavy day of fabrication or dust dislodged from overhead surfaces could raise that into the danger zone.

METHODS OF DUST TESTING

A combustion chamber is also used to test another key component of an explosion: the amount of oxygen needed to fuel it. Fire requires oxygen, but depending on how flammable a material is, it may burn even in an environment with low oxygen.

A spark igniter creates sparks to test the minimum amount of energy needed ignite a deflagration. Materials that are very easily ignited by even a small spark are a hazard in any situation where there is static discharge, even in the absence of any heat or flame.

A furnace is used to test how hot a material has to get before it will spontaneously ignite without a direct heat source. A cloud of dust may not burn even in very, very hot air unless there is a spark or flame to ignite it. If the dust ignites in the furnace, it means that temperature control is a key factor in handling this dust safely.

Some dust testing use a hot surface  to test whether dust will ignite when a surface with a layer of dust on it is heated. Again, some types of dust may not ignite even when exposed to very high temperatures unless there is a spark or flame, but some types of dust may ignite from being in contact with a hot surface, and this type of dust is dangerous anywhere that it could come into contact with hot materials.

IN CONCLUSION

These factors together are used to calculate a deflagration index, which is an overall rating of how likely that type of dust will produce a deflagration. This index is used to group dusts into explosion classes: Class 0 in non-explosive (silica), Class 1 is weakly explosive (charcoal, zinc, many food products), Class 2 is strongly explosive (wood flour, many plastics) and Class 3 is extremely explosive (aluminum and magnesium dusts, some plastics and other chemicals)