To The Limit – Understanding Exposure Limits


To The Limit – Understanding Exposure Limits

To the Limit - Understanding Exposure Limits


To see the article and the rest of Fab Shop Magazine Direct go here: http://magazine.fsmdirect.com/2017/may/d/#page32 or visit their website here: http://www.fsmdirect.com/safety/433-to-the-limit



Differential pressure in a dust collector is the difference in air pressure between the dirty and clean air sides of the filters. Most manufacturers recommend that you keep a regular log of the differential pressure measurements. But did you know it might also be required in your air quality operating permit?


Each state issues its own air permits to any business that is going to create any kind of air contaminant. There are different types of permits, depending on the state, the type of pollutant, and the size of the facility. Sometimes businesses are permitted to operate without a permit as long as they comply with certain regulations.




The EPA’s Clean Air Act applies to operations that are major sources of air pollution or particularly dangerous kinds of air pollution. If your company is required to have a Title V Permit, you have very strict regulations to follow, and are required to certify your compliance yearly. If you use baghouses, cartridge collectors, or similar types of particulate collection, a record of differential pressure monitoring is often required.


What if you have a state-issued permit, though? Does it say you have to keep a log of your differential pressure? And what happens if you don’t?


Your state’s air permits may require that companies using baghouses (the EPA and many state agencies refer to all fabric filter particulate collectors as “baghouses”) keep a differential pressure log. Others may not require you to keep a log, but might require that you take certain actions if the differential pressure indicates a problem.


If there is no log of your system’s normal differential pressure changes, you may not know when there’s a change indicating a problem. Unusually high differential pressure might indicate that your filters are being blinded off with dust, and they need to be changed. If the differential pressure is much lower than expected, it could mean you have a leak in your filters or somewhere else in the system.


If you don’t keep any kind of log of what your differential pressure is normally, you won’t have a record to show a state or EPA inspector who comes to renew a permit or to look into a problem. Even if your permit doesn’t specify that you are required to keep a log, it’s good documentation to show that you’ve been diligently monitoring your system function.




Dust collector manufacturers recommend keeping a differential pressure log, regardless of permits or regulations. Monitoring your differential pressure over time will allow you to see when your filters are getting close to needing changed. This lets you order and have replacements on hand, and it’s much more efficient than having to shut down a collector because the filters are so blinded off that they’re not working.


Monitoring can also alert you to other problems, such as leaks in the system that let the air take a shortcut around or through holes in the filters. Any sudden or big changes from your normal differential pressure should be a warning that something might be wrong.


Here’s an example chart from an electronic differential pressure recorder. Every application would have a chart that would look different. For example, the system in this chart only runs for one shift each day and does off-line pulse cleaning during breaks and lunch. You can see the pressure drop after each of these off-line cleanings during the day.


Differential Pressure Monitoring over a day infographic


How you record and monitor the differential pressure depends on your system. It can be monitored by having someone record the number at specified times every day, or by having an electronic monitor that tracks it. Each system’s normal differential pressure graph will look different. The point is to know what your system’s “normal” is so you can tell if anything changes.


If you do have an air permit, it probably contains some statement that you’re responsible for monitoring and maintaining your equipment to prevent air contamination. It might not specifically say that you have to keep a differential pressure record… but keeping that record is a great way to show that you have the monitoring and maintenance bases covered.




A spark trap (also called a spark arrestor) is a critical part of fire prevention in a dust collection system. They help block sparks before they can start a fire. We hope to answer some of your most frequently asked questions about our spark traps here. You can also watch the video below. If you need more information, please feel free to contact us.

  • How do spark traps work?

Our spark traps have impingement plates that cause turbulence and direct sparks and embers toward the walls of the spark trap, which knocks them around and causes them to lose heat. A screen blocks larger debris from passing through.



  • Why do I need a spark trap?

This is one of the most common questions. If there’s a danger that a spark could travel through your ductwork and ignite combustible dust or other materials, a spark trap may be an important part of your fire prevention system. If you need to know whether a spark trap will work for your application, contact us and we’ll help you find out.


  • What size spark trap do I need?

This depends on the size of your ductwork. We manufacture to fit almost all diameters. Our standard sizes are 6 inches to 40 inches but larger ones are available.


  • How do I connect the spark trap to my ductwork?

To make it easy to install, you can choose from three end types. We manufacture them with a raw end, a flanged end, and a quick connect end for clamping. Larger models can be heavy and may need hangers or other support.


  • Where in the ductwork does a spark trap go?

This is another one of the frequently asked questions. They can be installed vertically or horizontally. For proper functioning, the length of duct between the spark source and the spark trap should be at least one duct diameter, and between the spark arrestor and the dust collector should be at least ten times the duct diameter. A shorter distance will prevent the spark trap from working correctly and is not recommended. If you have a question about the length of ductwork, we suggest that you contact us for assistance.


  • What kind of maintenance does a spark trap need?

Our spark trap comes with a drop-down cleanout door that removes easily. This allows you to clean out debris and dust. There are no moving parts that need to be maintained.


  • Can they be used for high temperature applications?

If the temperature of air going through the spark trap will be higher than 200 degrees F, please contact us with details. There are options for higher temperature applications.


  • Does a spark trap work for every application?

There are some applications where spark traps will not be able to function properly. They do not usually work well for applications with wood chips or sawdust, or applications with sticky or fibrous material. We can help you determine whether a spark trap will work in your system.


  • Is your spark trap guaranteed to stop all sparks?

Another one of our most frequently asked questions. No spark trap is guaranteed to stop all sparks. Our design is as effective as a spark trap can be. A spark trap is an important part of a fire prevention system, but it should not be the only part. Our model meets all NFPA standards. We will take the time to help you decide what equipment will best meet your needs.




For any air filter, it’s important to know how efficient it is at filtering out dust and particles from the air. The problem is that not all dust is the same size. This will give you some idea of the different dust size that a dust or fume filter might have to deal with:

Dust size versus the MERV rating of a DeltaMAXX cartridge dust filter



A micron (also called a micrometer) is one millionth of a meter. As shown above, a human hair is about 80-100 microns. A sheet of paper is between 70 and 180 microns thick. Most fibers for use in making clothes are somewhere between 10 and 50 microns.

Here are some other things measured in microns:

BACTERIA – 1 to 10 microns

RED BLOOD CELL – 7 microns

MIST/FOG DROPLET – 10 microns




MERV stands for “minimum efficiency reporting value”. It is determined by testing a filter to find out what dust size it can filter. What’s important isn’t just the dust size, though. It’s also the efficiency: how much of that dust a filter can capture. There are three general categories of dust size used by ANSI/ASHRAE: E1, which is particles from 0.30 to 1 micron, E2, from 1 to 3 microns, and E3, from 3 to 10 microns.

The MERV rating tells you what percent of particles in that size range the filter will capture. Here are some examples:

MERV 6 – between 35 and 50% efficient for dust size bigger than 3 microns

MERV 10 – between 50 and 65% for dust size from 1 to 3 microns

MERV 15 – between 85 and 95% for dust size smaller than 1 micron



Your filter needs to have the right MERV rating for your dust size. For an industrial dust collector, this is especially important for meeting OSHA regulations, keeping your facility clean, and keeping the collector working efficiently.

Metal fume particles and other industrial dust can be smaller than 1 micron. If you look at the chart above, you’ll see just how small that is. It’s much smaller than many other things you can’t even see.

Metal fume and smoke particles can also be dangerous for your health, so it’s important that a filter catches as much of that dust as possible.

DeltaMAXX nanofiber filters have a MERV rating of 15. This means that they will capture between 85 and 95% of particles in the 0.30 to 1 micron range.

If your dust is very hazardous, like hexavalent chromium, you may need to add a HEPA filter. These don’t have a MERV rating: their rating is usually between 99.95% and 99.99%.

So why not use HEPA filters for everything just to make sure? First, they’re expensive. Second, catching that dust size means that the filters have to slow down the air a lot and have a lot of resistance. This isn’t necessarily what you want happening in an industrial air filtration system. For most industrial applications, MERV 15 is efficient enough.


We’ve talked a lot about how the Shadow handles weld fumes and meets the need for a powerful, portable fume collector in weld shops. The Shadow can handle a lot more than just weld smoke, though. Here are some of the applications this versatile source capture collector can handle:


Welding Source Capture with the Shadow



Instead of a fume arm, the Shadow can easily have a hose that attaches to other metalworking equipment, such as a cutting table. In a bigger shop, a cutting table might have its own fume collector. If your shop is smaller or the cutting table doesn’t get used all the time, the Shadow might be a great solution. You could hook it up to the cutting table, then easily roll it to the welding area, put the fume arm back on, and use it there.



Do you do grinding work that gets dust all over your shop, but not enough to need a full-sized dust collector for it? The Shadow’s source capture arm doesn’t just have to go over a welder. It can also go over any other dust-producing work area, like grinding or sanding. The collector takes up minimal floor space, and when you’re not using it, it’s easy to roll it out of the way.



In a woodworking shop, you might have dust being produced at a lot of different places, depending what you’re working on. One big dust collector could handle it all, but maybe your shop doesn’t need something that big, or maybe you just need something to handle one spot that’s extra dusty. The Shadow can move around your shop to wherever you need it, and the source capture arm adjusts to go exactly where you need it.



OSHA’s new silica laws are very strict about controlling exposure to silica dust. If you have stone cutting or grinding going on, the Shadow can be moved wherever it’s needed for source capture of silica dust. Not all portable collectors are built strong enough to handle abrasive particles like this, but the Shadow is designed to work on almost any type of dust. It can go from stone cutting to woodworking to a cutting table, and it can do it as often as you need it to.



If you’re collecting metal fumes, wood dust, or other combustible materials, a plastic collector could have a serious problem. If a fire occurs, a plastic collector could end up as a charred, melted lump, but the Shadow’s sturdy metal design will still be standing strong. If you’re going to be rolling a collector all over your shop, a cheap design that can’t handle the stress isn’t the best value. The Shadow’s nanofiber filter works with everything from wood dust to weld fumes and pulses clean for low maintenance and high efficiency.