proventilation

Down Draft Benches: The Truth About Return Air Flow

One of the latest trends in down draft benches is the addition of return air flow, also called air-makup. The idea is that re-directing the exhaust air back toward the bench will force more particulate down toward the filers, thus increasing the amount of dust that can be collected. There are several reasons why this is a bad idea.

Standard filters used in these systems are capable of filtering up to 99% of dust down to 1/2 micron, which is excellent. However, the 1% of dust that makes it through the filter is typically dispersed throughout the ambient environment to expose workers to safe levels of the dust. By redirecting the exhaust air back at the worker, the contaminated air is concentrated around the worker at the table. Additionally, this is air with the most dangerous dust. At 1/2 micron or less, the dust is easily ingested by the worker and is easily absorbed by the body.
The best scenario for airflow at the work deck is to pull ambient air into the system. The less disruption to this airflow the more efficient the equipment will be in capturing dust. The disruption caused by the return air flow blowing can create “eddys” (just like in a river) around the worker and/or the material being processed on the bench. This again can lead to the worker being exposed to higher dust levels.
It turns out that return air flow is an add on expense that just doesn’t make sense. It sounds like a nice option and it allows manufactures to under power the equipment to achieve a higher FPM (feet per minute) at the deck. Visit www.proventilation.com to see our full line of quality down draft benches.

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Wet Dust Collectors: The Need to Scrub

The Wet-Type dust collection market has been steadily growing over the past ten years for several reasons. Companies’ awareness of NFPA Guidelines has increased over this time period and they now realize that wet-type dust collection is a worthy and often necessary investment for their operation. The risk of a fire and the consequences which include significant production down time, employee injury or even death makes wet-type dust collection necessary in certain applications.
NFPA 484 is the Standard for Combustible Metals. This standard applies to the production, processing, finishing, handling, recycling, storage, and use of all metals and alloys that are in a form that is capable of combustion or explosion, as well as to operations where metal or metal alloys are subjected to processing or finishing operations that produce combustible powder or dust. (www.nfpa.org/484). If your process involves aluminum, titanium, magnesium, zirconium, tantalum, and/or niobium, NFPA 484 pertains to you. In most instances a wet type dust collection system is preferred for rendering these combustible materials inert. There are no expensive filters to replace, no chemical isolation systems to re-charge. While dry filtration systems become less effective as their filters load with dust, orifice impingement wet systems do not.
The cost of outfitting dry filtration systems with appropriate passive and active controls to comply with NFPA requirements has become prohibitively expensive. Passive controls involve special explosion vents and ducting to control pressure and to direct and extinguish flames. Active controls involve pressure/flame detection, and chemical isolation and extinguishing systems. These systems need to be regularly checked and re-charged, adding further to the cost of a dry filtration system. Wet collectors simply do not require these systems because the combustion hazard is removed immediately when the process material enters the water scrub.
There are two main types of wet-type dust collectors. The orifice / impingement design and the internal / venturi design. The O/I design utilizes a large cone-shaped orifice and an impingement plate that resides inside and on top of the cone. This creates an extremely efficient “scrub”. The scrub is where the dust entering the collector is mixed with water and sinks to the bottom of the collector and is the most important part of removing particulate. The process works best when the water surface to air ratio is highest within the scrub, thus making the most water to particulate contact. The O/I design does this most efficiently by removing 95% particulate down to 3 micron with just 3” wg of pressure drop. Additionally, by utilizing a wide opening in the cone, the O/I design will never clog.
A contributing factor increasing demand for wet-type dust collection is the increased use of materials suited for wet-type dust collection in products being manufactured. Aluminum and Titanium are the two most common metals where processes that create dust need to be rendered inert in a wet-type collection system. From aerospace to golf clubs, these metals are turning up in our products more often.
Other emerging markets for wet collection include food processing and pharmaceutical industries. Wet dust collection systems are used very effectively when process dust is water soluble and biodegradable. The wet system effectively captures dust where it is thoroughly scrubbed out of the air, dissolves, then simply drains away. There is no combustion hazard. There no exposure to workers by contaminated filters and little down time wasted by filter changes. Processing this way is less expensive and reduces a company’s environmental impact by avoiding costly trips to the land-fill with dirty filters. We have seen a move in this direction just in the past year. More and more companies are beginning to see that these simple advantages add up to significant savings and public relations advantages over time.
Currently, about half of the wet-type dust collectors we manufacture are stainless steel. Companies in the food processing industry are finding uses for wet-type dust collection and require the sanitary benefits of stainless steel for their applications. Stainless steel also increases the life of the dust collector approximately 70% making it an attractive option for companies willing to spend a little more money now and reap the benefits later.
Looking forward, companies are increasingly utilizing wet-type dust collection for unique applications that, we as a manufacturer, never considered. Recently a company had a process that created dust with a sticky residue. They were constantly replacing cartridge filters in their very large dry collection system. The ductwork required frequent cleaning and production needed to be halted during these maintenance operations. The process dust tested to be soluble and biodegradable and they are in the process of replacing a large dry cartridge dust collection system with a wet-type dust collection system. This solution will save the company hundreds of thousands of dollars in maintenance and production down-time in the coming years.
Wet-type dust collectors have been around since the late 1930’s. However, with today’s highly technical processes and materials, the benefits of wet-type dust collection is just beginning to be realized. Configurations such as piped systems, booth systems and down draft bench systems has allowed wet-type dust collection to be available for a wide range of processes. This, together with the small footprint requirements, elimination of expensive ductwork, and low maintenance requirements will continue to make wet-type dust collection more popular than ever in the coming years.

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Which Down Draft Bench is Right for You?

Which Down Draft Bench is Right for You?

Intercept PDB

Intercept PDB Dual Sided

Down draft benches are a common type of dust collection equipment used for sanding, grinding polishing and other fabrication techniques. Incorporated into the equipment is a work bench which has a grate to hold the material being machined. Air is pulled downward away from the worker, through the grate, filtered and then released back into the ambient air.
There are many configurations and options available for down draft benches. Dual-sided benches, side-panels, ceiling panels and lights are some of the most common options. They also come in many different sizes that you can choose from depending on your application.
High constant velocity at the work deck is one of the most important factors when choosing a down draft bench. If the equipment is not producing enough airflow at the work deck, the process dust may not be fully contained. Additionally, the further the process is away from the deck, the lower the capture velocity. Obstructing or altering the airflow by the process is also a consideration that needs to be addressed when assessing your requirements of a down draft bench. For instance, the worker simply standing at the bench can disrupt the ambient airflow and create small eddies of swirling air. Additionally the product being worked on itself can create these eddies. Picture a large rock in a stream and notice the rippling that occurs on the down-stream side of the rock. The more rocks, the more disrupted the water becomes. The force of the air movement into the deck of a down draft bench must be adequate to eliminate the risk of contaminated air being circulated into the breathing zone of the worker.
In recent years, dust collection companies have introduced the addition of return air flow ducts, commonly referred to as “regain air” to down draft tables and containment booths. The Idea is that by returning a portion of the exhaust air directly toward the table, airflow will be increased forcing material toward the work deck. This appears to make sense, and has quickly become a great sales tool for companies looking to increase their bottom line. Unfortunately, if we take a closer look at what is actually happening, this “add-on” will quickly become a dinosaur as it has no effect on truly increasing the performance of the down draft bench and actually inhibits the bench from doing its job as initially designed.
The main function of the down draft bench is to protect the worker from hazardous dust. Smooth and consistent downward flow on a broad scale is the most effective way to keep dust particles away from the worker. The more fluctuations in air movement, the more ineffective the bench becomes. By increasing airflow toward the bench at the distance of typical return air flow ductwork, pressure is increased in the vicinity of the exhaust; however the velocity at the work deck does not change. The fan is going to pull the same amount of air that it was designed to. This is because down draft benches operate at very low water pressure. The result is that pressure is increased above the worker which means that it will be decreased elsewhere. For example, if the equipment is pulling x amount of air evenly through the deck so that ambient air from the facility is entering the deck at the same speed directly in front of the worker as it is to the sides, this is optimal. Increasing airflow from the top (or from any direction), will allow less air will be pulled from somewhere else. Most likely airflow will be decreased near obstructions, like in front of the worker. Any disruption of air in the area of lower pressure such as the unfortunate placement of HVAC ducts or a forklift whisking by could be all the force that is needed to leach contaminated air into the facility or introduce contaminated air into the breathing zone of the worker.
Typical filtration of an 80/20 poly-cotton blend filter commonly used in down draft benches is initially 80% down to 1 micron. As the filter is used and accumulates dust particles, this efficiency rises. Sometimes a HEPA filter is added to the exhaust of the equipment to increase the filtration efficiency. Wet dust collectors vary in efficiency with the most efficient being the orfice / impingement design which filters 95% of dust down to 3 micron. Both of these filtration processes exhausting into ambient air or ducted outside of the facility bring down the parts per million of dust to an acceptable level within the facility. As an old saying goes in the business: “Dilution is the Solution to Pollution”. The problem with return air is that 50% of this exhaust is pushed back directly toward the worker and their breathing zone. This increases the ppm of harmful dust surrounding the worker exposing them to a potentially higher than acceptable levels of process dust. Additionally, the most likely particles to make it past the filtration process are the smallest and easiest to inhale and absorb by the body. These particles are so fine they can be suspended in air indefinitely. The more time the worker is in this contaminated zone, the higher the exposure to an unacceptable concentration of harmful dust.
Often you will find down draft benches advertised by CFM, but this is misleading at best. Just because a bench is 5000 CFM doesn’t mean that the velocity of air at the work deck is adequate. Depending on the area of open space of the deck, the velocity of air movement (referred to as FPM or feet per minute) can vary greatly. It is this measurement that allows you to determine if your bench is pulling with enough force to protect the worker. FPM of benches can range widely from 100 FPM up to 500 FPM. To increase FPM, some companies will sell a 2 foot by 4 foot bench, but decrease the actual area of grating, where air is being sucked in, so 8 square feet of bench actually only has 4 square feet of open grating or ventilated area. This, of course, decreases the effectiveness of the bench because the airstream is not broad enough to encapsulate the dust. Also, inspect the material covering the deck. This can be utilized to decrease the amount of ventilated area as well. Deck material can cover up to 80% of the deck to help increase FPM. For example, an 8 square foot bench (4×2) has a FPM of 300 and runs at 500 CFM. The ventilated area is only 4sq ft. If we increase the ventilated area to 7sq ft., and utilize almost all the bench, the CFM of the blower would have to almost double to provide the same velocity at the deck. Take note of this relationship to help compare the benches you are considering.
If you are in the market for a down draft table, look for a company that is open about the amount of ventilated area within the work deck compared to the actual size of the deck. Make sure that there is sufficient air velocity at the deck (FPM) to adequately capture dust particles from the process. Remember, the further away from the work deck your process is, the higher FPM you should be looking for. Protecting your employees is always your first concern, so don’t forget to pass on a company offering return air flow.

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Wet Dust Collection for Food Processing

What to do with all the dust?
We all love the smell of fresh spices, coffee and even garlic floating through the air. These aromas, however, can become quite irritating within a working environment. Our hair, clothes and lungs are penetrated by these fine dust particles and this is where issues begin to arise.
Continued exposure to dust can cause a variety of health problems including cancer. Fine airborne dust alone can cause its own set of health problems including breathing difficulties, respiratory pain, diminished lung function and weakened immune symptoms.
Food manufacturers, especially emerging manufactures, are quickly realizing that dust control is an important part of their processing needs to protect their workers and their products. Ventilation professionals know that, if possible, source capture is the best way to control dust. Capturing dust close to the point of release will prevent contaminants from becoming airborne and lower the ppm (parts per million) as close to 0 as possible. A ducted cartridge collector or a cartridge collector with an extraction arm can be most effective in this application.
Sometimes, a single point of dust collection just isn’t feasible as the application releases dust in too broad of an area. In this case, a booth collector may work best. By surrounding the application in a booth structure and the dust collector pulling air into the booth, filtering the air and releasing it back into the ambient air of the facility, the dust is never released into the facility.

Wet Dust Collection for Food Processing
Wet dust collection for food processing is relativity new. For over 40 years, wet dust collection has been primarily used for the collection of hazardous dust. Metals such as aluminum and titanium in dust form are highly combustible and must be contained in a wet dust collector to protect against explosions or fires. Over the years, employee health and safety has moved from convenience to necessity in the manufacturing and processing environment Typically, food processing dust collection has taken the form of cartridge dust collectors that utilize piping, explosion venting, complicated engineering to determine water pressure loss (Wg), frequent changes of expensive filters and exhaust considerations. Production changes required all of these factors to be re-engineered and often result in the purchase of new equipment to handle any increased dust loading.
In 2010, ProVent, the leading manufacturer of wet type dust collectors installed their first stand-alone system in a food processing plant in Trinidad Tobago. When initially contacted about the need for a dust collector, the discussions revolved around production down time for cleaning and filter replacement. Lingering spice dust was also an issue as the previous equipment was inadequate. A dust sample was requested for testing. The idea was floated about utilizing a wet dust collector to address the company’s issues. After testing the dust, it was determined that the material was soluble and was contained within the orfice / impingement scrub of the wet collector. The company proceeded with the purchase of the wet dust collector.
The benefits were noticed immediately. Down time for cleaning the equipment was reduced significantly and consisted only of upstream ductwork. The expense of purchasing replacement filters for the previous system was also eliminated. Since, the company has continued to replace their cartridge collectors with wet dust collectors throughout their processing facilities saving hundreds of thousands of dollars in future costs.
The orfice / impingement wet collector processes food dust in the same manner as metal dust. When dust laden air enters the collector, the heaviest particles make contact with the surface water and dissolve or sink to the bottom of the collector. Smaller particles must pass through a curtain of water before entering the “scrub”. The scrub consists of a wide area of turbulent water which creates high particle to water contact. After the scrub, particulate must pass through an additional water curtain before being released within a mist. The mist containing the smallest of particulate is buffed and drained back in to the collector. This process will contain 95% of dust down to 3 micron.
Sales of wet type dust collectors to food processors have increased dramatically since 2010. Approximately, 75% of sales to food processing companies have been stainless steel wet dust collectors and the benefits have been realized industry wide.

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Ambient Dust Collection

Ambient Dust Collection

Ambient Dust Collectors can be utilized for many applications by themselves, or in conjunction with other types of dust collection. These simple machines can improve employee health, working conditions and productivity. Typically, these units cost under $2,000.
Health problems can occur from almost all airborne dust. Factors such as concentration of the dust, particulate size, and dust source can emphasize these risks. Symptoms relating to airborne dust include itchy or redness of the eyes, skin rashes, breathing problems and sinus irritation. The continued exposure to such working conditions can also lead to more serious problems like cancer.
Particulate size can play a large role in increasing health risks. Larger airborne dust can often get caught within the nostril or sinus chamber. The smaller particles may reach the gas-exchange region in the depths of the lungs, where removal mechanisms are less efficient and more dangerous.
Some airborne contaminates, depending on their source, can be more damaging than others. Below is a list of contaminates that need to be contained and removed from the air.

• mineral dusts from the extraction and processing of minerals (these often contain silica, which is particularly dangerous)
• metallic dusts, such as lead and cadmium and their compounds
• other chemical dusts, such as bulk chemicals and pesticides
• vegetable dusts, such as wood, flour, cotton and tea, and pollen
• molds and spores

Employee exposure to airborne dust hurts productivity. Nobody wants to return to work after stepping outside and getting some “fresh air” if their work environment smells, makes their eyes itchy, or nose runny. Often people will treat their symptoms with over-the-counter drugs, which can have their own health effects or make employees drowsy.
Good dust collection is a necessity in almost all facilities. Despite quality source capture control of dust, many facilities still contain airborne dust. Does your environment have a particular smell? Do you have any of the symptoms mentioned above when you enter your facility? If so, the use of one or more ambient dust collectors can be used to clean or “polish” the air.