Spray Finishing

I find many construction-related companies who operate a spray booth at their shop. Many are used irregularity, depending on the project. As with most things that are used occasionally, they aren’t always in tip-top shape. Below are a few suggestions and questions for construction firms with these types of equipment.

  • Measure the airflow of your booth (there are various ways) but it should be 100 feet per minute. If it isn’t, you need to change something. The filter? the fan size? the exhaust duct size? the make up air (add more)? Please get someone to help you with this. Increasing the motor size is usually the knee-jerk reaction, but NOT usually the solution.
  • Make sure your manometer works. Is there a range written on the gauge for “operational”? see arrows at bottom of picture

  • Do your employees actually spray inside the booth? (seems like an obvious question but….)
  • Are your MSDS nearby?
  • Where do the employees mix the paint? (hopefully in a ventilated area)
  • Do the employees wear the correct PPE? What about during mixing? When the items are drying?
  • Are they covering their necks & arms when spraying? Do they need to? (check the MSDS)
  • What product do they clean their spray guns with?
  • What product do they thin the paint with?
  • Is there a functional eyewash station nearby?
  • Do you know the airborne level of exposures to employees?


When performing spray finishing activities with any product that contains isocyanates (diisocyanates, HDI, MDI, TDI) the minimum respiratory protection to be worn is a powered air supply respirator.

The reasoning is simple: isocyanates DO NOT have good warning properties.

Painters can usually tell when their cartridges are wearing-out, or getting “break through”. However, with isocyanates, the odor threshold is much too high to detect (it can be detected, but only at harmful levels).

In addition, isocyanates have a skin-notation, meaning that if the product gets onto the skin, it can be absorbed. As you can see, this employee was not wearing the proper PPE (personal protective equipment). However, when you’re a consultant, you have temper your comments. We did educate him and also told the general manager of our concerns and the reasoning.

On the plus-side, they had a manometer that was used and the employee knew when to change out the filters.  How this simple meter works is this:  A manometer measures the pressure differential between two different areas. In a paint booth it measures the pressure between each side of the air filters for the air coming into the booth. If the pressure gets too high, then the filters are clogged (or built-up). Notice the arrows on the bottom of the gauge to see when to service the filters. When the manometer (in this case) reads above 0.045 either the fan has to work harder, or the air escapes by the filter (in various ways- more information for another time)



To summarize,  there is no real quick-fix to this type of industrial hygiene assessment. Depending on what type of spray finishing you are performing- will depend on how to proceed. Here are some things to look during your assessments of these areas:

  • air flow across the face of the spray area should be at least 100 feet per minute
  • review the MSDS for the products you spray, and the solvents, thinners, and A+B parts-everything.
  • check the filters – are there scheduled changes? a manometer in place and used?
  • no flammables should be inside the booth area
  • watch the flow of work- usually there can be improvements- as well as lessons to learn
  • is the employees’ skin protected during spraying? (obviously not in the picture-right)
  • where does the waste (left over) spray product go?
  • ask employees about concerns and health issues

Typically respirators are worn in the spray finish areas. This list is not complete, but for starter, check:

  • what type of respirators are being worn? Are they protective enough?
  • what type of cartridges are used? Are they changed regularly?
  • are there scheduled change out times for their cartridges? where is that posted?
  • where are their respirators stored?