October 12, 2018
How to Test Your Range’s Ventilation System for Reliable Results
Like other technology in your range, such as your security and camera systems, you should regularly examine your ventilation system to ensure it is properly and efficiently functioning. The following provides an overview of this process.
Air Flow Speed
There are two points to consider when evaluating air flow speed on small arms indoor ranges. The first is the air flowing past shooters on the firing line. This should average 75 feet per minute (fpm), plus or minus 5 percent, and it should have minimal turbulence. The second point to be considered is the minimum air flow past the shooter’s respiratory zone — this can be anywhere the nose and mouth can breathe in contaminates, so you’ll need to consider prone and kneeling shooting positions as well as standing — which should be 50 fpm at any point.
These two rates are sometimes not fully understood by range designers, many of whom will design the average overall velocity at the firing line to be 50 fpm. But the intent is for the 50 fpm restriction to be the lowest velocity at any point. These two different velocities, suggested by the National Institute for Occupational Safety and Health (NIOSH), with air that is not turbulent, provide for exposures below OSHA’s allowable limits. The key phrase here is “not turbulent,” as turbulent air indicates varying air flow speeds, which could be lower than that 50 fpm rate.
Where and What to Test
The first places you want to test air flow velocities are at one, three and five feet above the floor in the center of each shooting stall. These positions equate to the respiratory zones of prone, kneeling and standing shooting positions, and the readings you get should meet the 75/50 fpm velocities as described above. The best instrument to use for these readings is the Shortridge Velgrid. If this is not available, any velocity measuring instrument that is calibrated to read velocities between 50 and 75 feet per minute can be used.
Pressure in the range, as referenced to the surrounding building area, is another element that needs to be measured. The range should be 0.05-inch water column negative (plus or minus 0.02-inch) as compared to adjacent spaces. This will prevent any contaminate created in your range from entering adjoining areas of the building where it can build up on surfaces (surface contaminate can be ingested).
Next, you’ll want to conduct a smoke test at the firing line. Light a smoke bomb and smoke each stall at its discharge side. All smoke should move downrange. If any smoke stands still or comes back into the get-ready area, modifications will need to be done to prevent contaminate created when shooting from flowing back into the respiratory zone. (Note: Before testing with a smoke bomb, clean the floor of the range to prevent the potential ignition of unspent gunpowder.)
You can also use a smoke bomb to test the direction of flow at the door/s into/out of the range. The smoke at the door/s should enter the range, and the smoke at the firing line should go downrange towards the bullet trap. You should self-test with a smoke bomb at least once per year, while your contractor or range ventilation specialist should perform a complete check of the system at least every two years. Watch a video of the smoke test here:
Other items to consider when evaluating your range’s air flow and pressure include:
- Shelves on your rear wall — These may create turbulence at the firing line. If you have turbulence issues and you have shelves:
- Remove the shelves and test to see if the turbulence is reduced.
- Replace the shelves with an open wire-type shelf that allows air to pass through it.
- Relocate the supply diffuser to an area in front of the shelves. (Note: there should be a minimum of 10 feet between the back of a radial diffuser and the firing line.)
- Material stored on the range — Brass barrels, garbage cans, target backers and other stored materials can create turbulence in the air flow. The area behind the firing line must be as free from obstruction as possible. If the smoke test shows turbulence, remove the stored materials and see if there is a better test result.
- Check for breaches in other areas — This should include looking for leaks around piping, door gaskets and sweeps and adjoining walls. We have seen many ranges where the juncture between the walls and the roof is improperly sealed. Breaches in your range walls may prevent you from maintaining the required negative pressure.
- Maintain equipment and filters — Keep proper tension on your belts, and change your filters at the recommended intervals. At some point, your filter loading can prevent your range from keeping its negative pressure.
About the Author
Bill Provencher has been a principal at Carey’s Small Arms Range Ventilation since early 1992. Carey’s systems provide customized air handling using top-grade filters and other components to expel airborne ballistic contaminants and evacuate smoke downrange. The company has designed and built hundreds of range ventilation systems, each of which is tested and guaranteed to meet OSHA, NIOSH and EPA requirements.