Evaluating Machine Shop Air Quality
May 7th, 2025 | Posted in Air Cleaners
There’s coolant mist in the shop air. There’s been coolant mist in the shop air since we’ve been using coolants and especially so now that high pressure coolants have become more common. Until now we haven’t thought much about it but if you’ve been reading the previous blogs on this site, you know that here are potential health hazards associated with many of the components of coolant mist. We have to wonder if there isn’t some relatively easy way to take a first cut at whether the coolant mist represents a health hazard. Yes, there is. There is a profession called Industrial Hygiene devoted to evaluating potential airborne health hazards among others. We can take advantage of the tools of the Industrial Hygienist (IH) to make an preliminary determination if there may be actual health hazard from the coolant mist. An initial screening can be made by measuring the respirable particulate (coolant mist is a particulate) in the shop air and you can do this yourself.
Usually, evaluation of shop air quality is done by an IH working as a consultant or working as a loss control specialist with your Worker’s Comp provider but there are circumstances that suggest the DYI approach. For example, consulting IH work can run a couple of thousand dollars a day and the company budget may not accommodate that expense. You can often find a consulting IH by going to the American Industrial Hygiene Association (AIHA) website at https://www.aiha.org/consultants-directory but the population density of IHs is quite low in many parts of the country and there may not be an IH in reasonable commuting distance. It may also be possible to make an arrangement with your Worker’s Comp loss control specialist to come to your shop and evaluate coolant mist concentrations but you may or may not be comfortable with that approach. Or, you may just prefer to do it yourself just to see what you find out.
Fortunately, evaluating respirable particulate is easy. The first step is contacting an AIHA-Accredited laboratory, open an account (we always have to do that!) and ask them to send you a calibrated pump and filter (called a “sample train”) for respirable particulate. This writer has worked with SGS GALSON (https://www.sgsgalson.com ) labs for a number of years and they have proven to easy to work with. You’ll get the pump and sample train in a tool box. Open it up, take out the sampling pump and sample train and put it in a location where it won’t be disturbed but will be representative of the air breathed by people in the shop. Avoid putting the sample train in the air flow from a shop fan or the exhaust from a mist collector – that high speed airflow will interfere with air flow into the sample train.
Next step is to turn the pump on (they are battery powered) at the beginning of the shift and record the start time. At the end of the shift turn the pump off, record the stop time and send the pump and sample train along with the start and stop times back to the lab for analysis. You’ll get the result by email.
This is a screening technique that measures “Particulates Not Otherwise Classified (PNOC) and does not identify specific coolant mist components. The OSHA Permissible Exposure Limit for PNOC is 5 mg/m3. It has been this writer’s experience that if the initial result at PNOC is above 1 mg/m3 and people in the shop still voice complaints it may be a good idea to investigate further and identify the specific components of the coolant and then re-evaluate with methods designed for those components. Some of these components have exposure limits well below 1 mg/m3. For example formaldehyde which off gases from some biocides when mixed with water has a ACGIH[1] Threshold Limit Value (TLV) of 0.37 mg/m3. If you get to this point it would be appropriate to consult with an Industrial Hygienist.
It should be noted that there is also a method and an ACGIH TLV of 5 mg/m3 for “Mineral Oil Excluding Metal Working Fluids.” The reason the ACGIH does not apply this TLV to coolant mist is given in the Documentation of the Threshold Limit Value for mineral oil:
“Although exposures to mineral oil aerosols in metal working industries are associated with respiratory symptoms and cross-shift declines in pulmonary function, additives and metal or microbial contaminants are present in the metal working fluids and it is unclear which components are responsible for the effects observed in epidemiology studies. Therefore, the TLV–TWA for mineral oil does not apply to occupational exposure to mineral oil aerosols encountered in metal working operations.”
In any case, the closer the results are to 5 mg/m3 the more obvious the need for coolant mist control.
In summary, the PNOC data can be used as a simple screening tool to indicate if further evaluation with the help of an Industrial Hygienist may be prudent. Monitoring for actual personal exposures requires a technique called “Personal Breathing Zone (PBZ) Monitoring.” There are important nuances involved in using the PBZ technique, e.g., determining exactly what chemical to monitor for and what sample media to use for those samples. Also, the area airs quality evaluation and the PBZ data must be made available to the monitored or affected worker(s) per 29 cfr 1910.20, Access to Medical Records and must kept in a file where it can be inspected by OSHA. Therefore, working with an IH professional is recommended to ensure quality results.
Also, if the PNOC data indicate a need for mist collection equipment, this method can be used as a “Before and After Installation” evaluation of the efficacy of mist collection equipment installation.
Air Quality Engineering offers a wide range of mist collection equipment utilizing impingers, electrostatic filters and media filters for nearly any application. If you would like to talk with an Industrial Hygienist about evaluating the coolant mist concentrations in your facility, Air Quality Engineering can put you in touch with this writer.