According to IQS Directory:
Chapter One – What is a Dust Collection System?
A dust collection system is a system that removes particulate contaminants from the air in production facilities, workshops, and industrial complexes. The system cleans air by forcing it through a series of airtight filters. Once the air is cleaned, it is expelled outside or recirculated, after it has achieved the proper emission’s standards.
As concerns for the environment have grown, dust collection systems have become a necessity for industries that produce large amounts of dust particles and ambient gases. Manufacturers of dust collection systems are required to adhere to strict government guidelines and assure their customers of the efficiency of their systems as well as their compliance with EPA, NFPA, and MSHA standards.
Chapter Two – How a Dust Collection System Works
In simple terms, a dust collection system is designed to remove particulates from the air produced during a production operation. This short definition is an extreme simplification of the ingenuity required to design and produce a means of capturing harmful contaminants.
The basic components of a dust collection system include a blower, dust filter, cleaning system, receptacle, and means of collecting the particulate matter. The common types of dust collecting equipment include fabric filter baghouses, inertial separators – sometimes referred to as mechanical cyclones, cartridge collectors, wet scrubbers, and electrostatic precipitators. Baghouse dust collectors are the most commonly used since they have a 99% efficiency.
The types of pollutants removed differ according to the industry. Dust collector manufacturers design and develop equipment to specifically meet the needs of each environment condition.
How a Dust Collection System Works
Dust collection systems have ductwork to draw in the air, an air purifier, and dust collector. These basic elements are configured differently for each type of system.
The first consideration when designing a dust collection system is the ductwork, which may seem to be simple but has to be carefully considered to ensure proper performance of the system. The size of the pipe used depends on the tool size, air requirements, length of needed pipe, number of machines being serviced, and the types of particulates being extracted. The design below is of a single machine dust collection system with the size of pipe needed for this configuration.
Though a fan or blower may have a simple design, when installed in a dust collection system, several factors have to be considered. First of those factors is the volume of air that needs to be moved. This is measured in cubic feet per minute (CFM). The next consideration is the static pressure throughout the whole system. Other variables are the temperature, substances in the air, and the level of moisture.
The blower or fan is a critical element in a dust collection system since it is the mechanism that pulls the contaminated air into the ductwork away from the workplace and sends it to the filtration and cleaning systems. The basic types of blowers are centrifugal and axial. The centrifugal type has wheels in a housing, while the axial type has propellers.
Dust Filter –
The dust filter is the air cleaning portion of the dust collection system. There isn’t any one standard of dust collection filter. In essence, the blower pulls the air from the location into the filter that removes the particulates from the air. The air to cloth ratio is the amount of air that passes through a square foot of the filter. The lower the ratio, the higher quality of the filtration systems efficiency.
Dust Filter Cleaning System –
As can be imagined, the filtration system for a dust collection system can become filled and clogged as particulates build up on the surface of the filter. There are a variety of methods used to clean filters some of which involve shutting down the system. For systems that have to be in continuous operation, this is not an option and during operation alternate methods have to be used.
An on-demand system has a controller with a pressure sensor for monitoring the static differential on the filter. As the system measures the pressure on the filter, when the levels are too high, it sends a signal to a diaphragm valve to release compressed air into the filter to remove the accumulated particles. This is referred to as a pulse jet baghouse or pulse jet dust collector and is the most common form of particulate air pollution control equipment.
Other systems produce an alarm to advise operators that a significantly high pressure has been reached. Most systems, whether they are on demand or not, have control devices that make operators aware of a collection failure or drop in pressure across the filter.
The short video below describes the high velocity method of filter cleaning from Scientific Dust Collectors. Their system of cleaning uses a high pressure air system that efficiently cleans the filter without causing excessive wear.
Once the particulate matter passes through the system and is removed from the filter, it falls into a container or receptacle for collection. The design of the container depends on the type of material being filtered and its loading rate. The main types of mechanisms are:
- Enclosed box – collected material is funneled into a receptacle.
- Drum or bag – a mechanism that requires replacement of the drum or bag that collects the matter.
- Rotary valve – similar to the drum or bag, matter flows through a valve into a drum or bag.
- Screw conveyor – a conveyor system that moves matter along to a storage or disposal location.
Electrostatic Precipitator System –
Though filtration systems are a popular form of dust collection, there are systems that do not use filters. One of these is an electrostatic precipitator, which uses the force of electrostatic energy to remove particles from the air and has discharge wires and collecting plates. As particles pass through the system, they are ionized and charged, which causes them to be accumulated on a collecting plate. From the collecting plate, the particles are removed by rapping or vibration. The process can be seen in the diagram below.
Chapter Three – Types of Dust Collection Systems
Dust collection systems are a critical part of several industries. Their design and engineering have to match the needs of the industry where they are being used with the main purpose of controlling, reducing, and removing contaminants, harmful matter, gas fumes, and dust. They are engineered to purify and filter air such that it can be released into the surrounding environment or back into the workspace.
Each industry has a different array of pollutants and harmful particles to be removed. Dust collectors must meet the specific extraction needs required by each industry to provide optimum air purification.
As the standards for clean air have become more rigid, manufacturers of dust collection systems have risen to the demand and produced air purification devices that meet and exceed government requirements.
Types of Dust Collection Systems
Shaker Dust Collection Systems –
The shaker design of dust collection systems is a baghouse system that shakes the fiters to release the particles into the collection bin or hopper. They operate using one of two systems, which are compartmentalized or when the air flow is stopped. The compartment design is more practical since it allows for continuous operation without needing to take the whole system offline. They are used where it is not possible to supply compressed air to clean the filter such as foundries, steel mills, mines, and smelting plants.
Cyclone Dust Collection Systems –
Cyclone dust collection systems are a form of inertial separator that uses centrifugal force to separate particulates. The cyclone is created in a self-contained chamber where the air is purified by cyclonic action. The circulated airflow, which is somewhat similar to a vortex, pushes the heavier contaminates against the walls of the chamber. Once collected, they slide down the sides of the chamber into a collection hopper. They are used by woodshops, paper mills, shot blasting processes, and grain mills.
Baghouse Dust Collection Systems –
The most common form of dust collecting system is the baghouse. It is the most efficient system that uses a fan to create a vacuum to force contaminates through a filter in a bag. Baghouse methods are divided by how they clear their filters. The shaker method shakes the filter to remove the collected dust. The jet version uses a burst of air when a sensor detects the filter is full. The reverse air method forces fresh air through the filter. Some of the industries that use baghouse systems are powder coating companies, cement plants, paper manufacturers, and rubber recycling.
Dust cakes on the outside of the bags and is removed down into collection hoppers by a blast of compressed air or being shaken. They operate continuously to collect any size particles. The design of the system allows for easy access for maintenance.
Spark Arrestor –
Spark arrestors can be addons for systems that have some form of combustion. They trap exhaust and lower the temperature of heated particles before they enter a dust collecting device. Industries that are involved in heating of metals commonly have spark arrestors as a safety measure. Spark arrestors are required to meet the specifications of the National Fire Protection Association (NFPA) number 69. They channel sparks and embers away from the dust collection system, where the sparks are cooled to prevent explosions and fire.
Cartridge Dust Collection Systems –
The cartridge dust collecting system replaces bags with cylindrical or oval shaped cartridges that are open on both ends and are lined with pleated filtering media. One end of the cartridge is sealed with the open end used for clean exhaust. The air stream is forced through the outside of the cartridge to the inside. The cartridges are kept clean by compressed air blown into them, which removes built up dust that falls into the hopper below.
Wet Scrubber Dust Collection Systems –
A wet scrubber dust collection system uses droplets of water to capture the dust particles. The system has two whirling blades that turn in opposition to each other. The first blade pulls the dust ladened air into the mechanism and saturates it with water. As the rotation accelerates, a mist eliminator forces the watered dust particles into the disposal unit. When the dust particles are soaked with water, they increase in size, which makes them easier to remove. Types of scrubbers include gravity spray towers, cyclone spray chambers, impingement scrubbers, packed bed scrubbers, and venturi scrubbers.
Downdraft Table –
Downdraft tables are self-contained dust collection systems that suck particulate matter from the table into a filtration system. They are portable dust collection systems that function as a workspace and are used for small jobs. They are normally made of steel with a powerful suction motor. Downdraft tables are referred to as extractors or grinding tables. To allow for airflow, the top of a downdraft table is perforated. The size of the perforations influences the airflow and efficiency of the table.
Self-Contained, Internal Return Dust Collection Systems
A very viable solution for dust collection for processes that create dust as part of manufacturing and processing is a self-contained, internal return dust collection system that uses a set of fans, filters, and collection bags to remove dust from workstations and manufacturing. Unlike dust collection systems that send environmental air to a filtering system, a self-contained, internal system removes dust where it accumulates and sends it to be filtered and collected.
This type of system is the least expensive but extremely efficient. It is designed to collect wood chips, plastic particles, and materials that accumulate on solid surfaces. The system is completely self-contained meaning that it does not discharge air into the atmosphere and comes in sizes to fit any operation.
Chapter Four – Benefits of a Dust Collection System
As the number of regulations and standards for air pollutants rise, dust collection systems are becoming a necessity, though at one time they were considered to be an add on luxury. Manufacturers of dust collection systems keep strict watch on government standards and design systems that expertly adhere to the requirements.
Aside from the various regulations, there are practical reasons for installing a dust collection system. The first consideration is the protection of the health of workers who have to work in gas filled and dust saturated environments.
Benefits of a Dust Collection System
When making the decision as to installing a dust collection system, there are certain factors that should be considered. Though less expensive systems may be more attractive for financial reasons, the most important factor is the quality of the air in the workspace and the area around the facility.
Fire Suppression –
Whenever there is a concentration of dust and gas, there is always the potential for fire. By having a dust collection system, especially one with a spark arrestor, the concern for fire is significantly reduced. A dust collection system has dust constantly moving, which prevents it from collecting and becoming a hazard.
Prior to the development of dust collection systems, dust explosions, especially in woodworking shops, were very common. The problem was so prevalent that many shops had a wall that was open to the outside. Much like fire prevention, dust collection systems keep air moving and circulating to prevent the possibility of dust collecting sufficiently to produce an explosion bubble.
Odor Reduction –
Air in a dust collection system is constantly circulating and being refreshed, which assists in keeping odorous contaminants out. Though dust collection systems may get confused with air conditioning, they have far more benefits. When polluted air is sent through filtration, it removes the contaminants and the odors that they create.
Respiratory Health –
One of the major areas of concern for the Occupational Safety and Health Administration (OSHA), the National institute for Occupational Health and Safety (NIOSH), and the Center for Disease Control (CDC) is the safety of the workspace for workers. Regarding dust and contaminants, they have specific requirements regarding the allowable percentage of particulates in a cubic foot of air. Violation of these standards can lead to a business being closed, which makes the installation of an acceptable dust collection system essential.
Personal Safety –
Something that is rarely considered in an industrial environment is the quality of the floor and whether it is clean. One of the benefits of a dust collection system is the removal of the need to constantly clean the floor. There may be slight accumulations during a workday, but a dust collection system significantly reduces the need to sweep the floor or dust off a workspace.
Worker Morale –
Psychological studies have proven, such as the Hawthorne Study, that a clean well lit work environment produces more productivity and improved worker morale. Workers who are not constantly confronted with offensive odors and unclean workspaces tend to enjoy their workday and are more productive. A dust collecting system is an essential factor in producing the ideal conditions. In many ways, investing in a dust collecting system can be beneficial to the bottom line.
Governmental Regulations –
Of all of the motivating factors for the installation of a dust collection system compliance with government regulations is the most important factor. Companies that do not have the proper particulate percentage can be fined or forced to cease operations. OSHA and NIOSH closely monitor potentially harmful working conditions and do random inspections.
Chapter Five – Manufacturing Operations that Use Dust Collection Systems
A dust collection system is essential for any industry that produces gases, dust, overspray, or other forms of particulate matter. These highly technical and efficient units, which were once thought to be only part of a woodworking shop, have become common in a wide variety of industrial operations.
Operations that Use Dust Collection Systems
Many of the operations that use dust collection systems are mainly concerned about safety since several operations involve the use of gases.
Plasma Cutting –
Plasma cutters produce fine smoke and fumes, which need to be removed for the protection of the operator. Dust collection systems for plasma cutters use specially designed downdraft tables to draw the fumes away from the workspace and worker.
Welding fumes contain particulate matter and various forms of gases, which are in the workspace of the welder. There are various types of dust collection systems that are used to capture and collect the hazardous matter produced by welding. Since welding fumes and dust can be explosive, the material produced must be tested for its fire and explosive characteristics in accordance with OSHA and the National Fire Protection Association’s (NFPA) standards.
The most common form of system used for welding operations is a cartridge filtration, which is highly efficient at capturing small particles.
Seed and Grain Operations –
The volatility of the dust from seed and grain operations is so high that OSHA has a set of standards that are specifically designed for these operations. Dust from seed and grain operations varies according to the types of materials being moved. It can be abrasive, sticky, or extremely fine. This is further complicated by the wide variety of equipment used in seed and grain operations, which include conveyors, elevators, bins, various forms of vents, silos, and mixers.
The most common form of dust collecting system for seed and grain operations is a baghouse collector since they can be easily placed in hard to reach locations or places with limited space. Baghouse collectors are used for their high efficiency of 99% and reliability.
The initial concern for air quality in the workplace began with woodworking since it produces large volumes of saw dust and fumes. As producers have investigated the various woodworking operations, they have found that there is a wide variety of particulate matter that is produced. The determining factor is the type of work that is being done.
Lumber mills and sawmills require a different type of dust collection system than that which is used by a wood pellet manufacturer. Each type of operation requires a different form of collection system.
Regardless of the type of woodworking operation, wood dust has been found to be the major cause of dust accidents. The dangers of dust from woodworking operations are highly underestimated. Wood dust easily ignites and spreads rapidly, which makes having a dust collection system essential.
The two types of dust collection systems for woodworking operations are cartridge and baghouse with baghouse being the most efficient. Regardless of the type of system chosen, it has to be designed and engineered to specifically fit the operation and production process of the customer.
Food Processing –
The central concern for dust collection systems in the food processing industry is transport, storage, and mixing, which are the areas that accumulate the most dust. Sugar, powders, flour, meals, spices, and starch are materials that produce dust that needs to be controlled and monitored.
The processing of food involves the use of conveyors, packing equipment, mixers, shelling machines, and concentrated storage areas. Filtration systems can be connected to each of these types of equipment and locations. The special needs of food processing require the use of stainless steel since it is approved for operations involved in food manufacturing.
The two agencies that regulate air quality for mining operations are the Environmental Protection Agency (EPA) and the Mine Safety and Health Administration (MSHA), a branch of the Department of Labor. The main concern for mining regulations is silicosis and black lung disease.
Dust control systems for mining operations have to be able to withstand heavy use but flexible enough to adapt to the wide variety of conditions. The nature of mining dust requires very sturdy and reliable equipment since mining dust can be rough and abrasive as well as extremely fine. The various types of mining determine the type of dust collection system. Dust from rock mines tends to be less combustible and unstable while dust from coal mines is highly volatile.
Regardless of the operation, mining dust control systems are designed to suppress explosions, isolate fumes, and control odors from gases. The common types of dust collection systems for mines are baghouse and cartridge.
Fiberglass dust is a very serious and a dangerous health risk since it can cause eye, skin, and lung irritation. The size of the dust particles varies depending on the type of operation with certain resins having the potential of being combustible. Fiberglass is composed of silica and other minerals, which is extruded and reinforced with resin. The dust particles from fiberglass tend to stick together regardless if the process is grinding, cutting, or some other form of shaping.
To meet the standard of OSHA and NFPA, fiberglass dust collection systems are required to have fire and explosion protection components. The air quality for fiberglass dust control systems is closely monitored due to the health risks. Cartridge dust collecting systems are normally used for fiberglass operations.
The challenges for foundry dust collection systems revolve around crystalline silica dust, carbon monoxide, and heat, which are a toxic combination. These factors make meeting air quality standards difficult and demanding. When selecting a dust control system for a foundry, the first consideration is the ability of the unit to withstand the harsh and hazardous conditions of the workplace.
The environmental conditions of a foundry make the selection of the proper dust control system difficult. Aside from the obvious conditions, the selected equipment has to meet the regulations of OSHA, the EPA, and the NFPA. To meet those standards, dust collection systems employ shakeout enclosures, collection hoods, melt, mold pouring, and cooling hoods as well as exhaust stacks.
Pleated bag style collectors, cartridge style, have a highly efficient filtration system as well as a compact size and reduced pressure drop. In operations where there are lead or silica particles, a HEPA after filter is added to ensure zero emissions.
Coating or thermal spray applies heated material to metals to coat their surfaces. Dust collection systems for this type of operation have to be specifically designed to fit the type of coating being applied. The purpose of the system is to control and minimize overspray and dust.
The typical thermal spray dust control system uses ducts to move air to the collection device. The duct work is attached to the booth or cell where the spray is being applied. Though it would seem likely to increase airflow and movement, this type of solution may waste energy and not be efficient. The design of the booth is dependent on air that enters the cell or booth and at what force. For most systems, it is important to have a slight vacuum in the booth to avoid possible positive pressure.
One of the more efficient designs is to have a makeup air connection opposite the air extraction unit, which creates cross ventilation. Another method is to simply place the makeup air connection on the top of the booth. Regardless of the design, it is important for the cleansing of the air to have cross ventilation.
Much like a cleanroom, airflow in a thermal spray booth can be either horizontal or downward, though the downward design is best for dust collection systems. With the downward design, the floor of the booth is a grating, a design that takes advantage of gravity for air movement.
The pharmaceutical industry is one of the most highly controlled industries with very extensive and precise regulations. Dust from pharmaceuticals is generated mostly during the production and packaging of products. Each of the various steps of producing a drug, which include granulating, drying, mixing, pressing, coating, and grinding, all produce large amounts of dust that needs to be removed. The dust produced can easily migrate across the factory floor and contaminate workers and other products. Intercepting and controlling this dissemination is the function of the dust control system.
When designing a dust control system for a pharmaceutical plant, the first consideration is mapping the ventilation system to track the path of dust, fumes, existing airflow patterns, and possible evolutionary changes. Since many pharmaceutical dusts are combustible, the design of the ventilation system is extremely critical.
The two types of dust collection systems used by pharmaceutical concerns are baghouse and cartridge since the filters do not have to be replaced that often and are self cleaning through pressure air spray. HEPA filters are commonly found in pharmaceutical dust control systems since they are the most efficient and reliable. As with a foundry system, they are installed as a secondary protection to achieve zero emissions.
Chapter Six – Materials and Particles Removed by Dust Collection Systems
Although dust collection systems are designed to collect all forms of particulate matter, certain systems perform better with specific materials. When manufacturers are choosing a dust control system, they are advised by producers about the type of system that would best fit their needs since purchasing and installing a dust control system is a major investment.
Types of Materials and Particles Collected by Dust Collection Systems
Particulate matter comes in a wide variety of forms from silicon dust to wood chips and sawdust. The type and design of the dust control system for each type of matter is differentiated by how efficiently and economical it removes dangerous materials. Below is a short list of the types of particles that dust collection systems can remove.
Gypsum – Gypsum requires a high efficiency baghouse system capable of operating at temperatures near 220°.
Felt – Felt is used in the production of apparel and requires dust collection systems at three stages of the process.
Glass Recycling – The glass recycling process produces very fine silica dust and requires the use of Teflon bags to remove the particulates.
Carbon – Fine carbon dust can be found in a wide variety of production processes and is removed using polyester filters.
Molybdenum – Molybdenum dust is created during the mining process and is removed using a baghouse system.
Spice Dust – Spice dust is created by the production of any form of spice from cinnamon to sesame seeds. Dust collection systems are necessary in warehousing and processing plants.
Metal Chips – Grinding operations produce metal chips that need to be removed for the safety of workers. Baghouses and scrubbers are used for airflow filtration.
Sawdust – This is the most common of the material removed by dust collection systems. Cartridge or baghouse methods can be used with baghouse being the most efficient.
Aluminum Dust –There are several types of aluminum forming operations that produce aluminum dust such as polishing and sanding. Fabric filter bags in a cartridge system prove to be the most efficient method for collecting the dust.
Cement –Cement dust is created during the movement and transport of the product. Dust collection systems are covered to contain the dust and clean the air.
Clay –Clay dust is produced in the production of bricks. Dust collection systems are used to capture random clay pieces.
Plastic Dust – High Density Polyethylene (HDPE) dust is produced in the production of plastic panels when they are being shaped and formed on an edge trimmer, grinder, or miter saw.
Paper Dust – One of the more common forms of dust is paper dust that is the side effect in the production of various types of paper. In the past, workers wore face masks and ventilators. With the introduction of dust collection systems, workers are safer and more protected.
Sugar – Sugar dust is the by-product from the production of candy. Pulse jet systems are used to keep the filters of the dust collection system particulate free. The collected material is removed and collected in drums.
Zinc – Zinc dust is produced in the galvanizing process. Dust collection systems remove chemicals from the heating process. A baghouse system is the preferred system.
Rice Dust – Rice dust has very fine and minute particles that accumulate during the production of rice based products. A dust collection system is required for the protection and safety of workers.
Silica – Silica is one of the most common substances on earth and is a central part of several production operations such as the production of glass, ceramic tile, cement, and asphalt. OSHA has increased the restrictions on the control of silica dust, which has forced producers to install highly sophisticated dust collection systems.
Cosmetic Powders – The production and manufacture of cosmetic products creates a great deal of dust that easily migrates to all areas of the production facility and makes the air hazardous. To control the problem, producers install dust collection systems such as baghouse and cartridge types.
Shot Blasting – Dust collection systems for shot blasting and sandblasting are needed to collect the blasting material, debris, and dust. The blasting process is used to prepare the surface of metals for painting and coating. The material from the process can damage equipment. The dust collection system assists by removing blast material.
Rock Dust – Rock dust collection systems are used at quarries and mining operations. They are heavy duty equipment designed to operate in harsh and hazardous conditions. Their main function is to control ambient dust that is a part of the mining process such that it does not spread from the area of the operation.
Chapter Seven – Dust Collection System Regulations
With growing concern for the environment, dust collection systems have become a vital part of several industrial and manufacturing operations. Government regulatory agencies regularly publish regulations and standards regarding the permitted quality of air released from production facilities. The organizations and administrations that focus on air quality are the Occupational Safety and Health Administration (OSHA), the Mine Safety and Health Administration (MSHA), Environmental Protection Agency (EPA), the National Institute for Occupational Safety and Health (NIOSH), and the National Fire Protection Association (NFPA).
Dust Collection System Regulations
Though OSHA does not have dust collection system regulations, it does have regulations regarding the amount of dust that can accumulate in a production facility. There are requirements regarding combustible dust particles and how they are removed. The main focus of OSHA standards is a stipulation of the precautions being taken by a company to protect the health of its employees.
Regardless of the absence of dust collection standards, OSHA does prefer that manufacturers have a dust collection system to control dust accumulation. The regulations regarding dust collection relate to the factors for keeping employees safe.
OSHA does have regulations related to exposure to dust and describes the types of dust that are harmful and dangerous. The organization has published exposure limits for each form of harmful dust.
In 2020, OSHA published specific regulations regarding silica dust in an effort to reduce the exposure to crystalline silica.
OSHA Regulation 1910.272 is specifically written to cover the standards required for seed and grain operations. It covers in detail the various operations that expose workers to harmful dust.
Since dust and its accumulation is a potential fire hazard, the NFPA has developed requirements and standards for dust collection systems regarding fire and explosion suppression.
NFPA 68 – specifies how fires should be vented
NFPA 69 – delineates procedures for explosion control
NFPA 652 and 654 – are the standards for safe and controlled handling of combustible materials and dust
NFPA 484 – describes the procedures for handling combustible metals
The EPA regularly reviews air quality standards as specified by the Clean Air Act’s National Ambient Air Quality Standard for Particulate Matter. The agency has established Dust Lead Hazard Standards (DLHS) under the Toxic Substance Control Act (TSCA). The stipulations of the DLHS are guidelines for health inspectors.
MSHA-P13-03 – covers the sampling procedures for mine respirable dust samplings.
Under the Continuous Personal Dust Monitor (CPDM) certification system, mines have to apply for certification every three years with a personal examination that shows competency in sampling procedures, maintenance, and calibration.
Phase III of the program implemented in 2016 has specific respirable dust rules:
- The concentration limits for respirable coal mine dust are 1.5 mg/m3 at underground and surface coal mines.
- The concentration limits for respirable coal mine dust are 0.5 mg/m3 for intake air at underground mines.
The NIOSH has established standards for rating filtration systems, which is governed by Part 84 of Title 42 of the Code of Federal Regulations. Mechanisms designed for respiratory protection are classified under air purifying respirators and chemical protection cartridges.
NIOSH classifies respiratory systems by their efficiency level when exposed to lubricants, cutting fluids, and glycerine, to name a few. When a filter is tested, it must demonstrate a minimum efficiency level as set by the NIOSH.