Paint Spray Booths

Downdraft booths offer the best protection.

Types

Spray painting should always be done in a well-ventilated spray booth - defined as a separate room with a ventilation system.

Manufactured spray booths can be purchased and installed, or booths can be custom made. Either type works well to protect workers and produce good painting jobs.

The type of ventilation makes the most difference in how well the booth works.

Priming in a prep station protects other workers and the paint job.

Priming is usually done by autobody technicians rather than painters and is often done on the shop floor. This practice can cause significant exposures to other technicians in the area!

Many shops have invested in prep stations for both sanding and priming. Prep stations are portable spray booths with ventilation and filtration of the exhaust air.

Downdraft

Spraying of sealer, basecoat, and clearcoat is almost always done in a spray booth to protect both the workers and the paint job. The most effective paint booths are downdraft booths which supply filtered air to the booth through its ceiling, and exhaust the chemical-containing air to the outside after it passes through filters below the grating on the floor. In these booths the air is directed downward, and the paint vapors and overspray are carried downward. So, they do not even pass by the painter’s breathing zone.

Semi-Downdraft

Semi-downdraft booths, in which the air either comes in through ceiling filters and goes out at the back of the booth, or comes in through the door and exhausts through the floor, can also be effective. In these booths the position of the painter is crucial. Whenever possible the painter should orient himself so that he is upstream from the paint being sprayed, aiming the paint gun in the direction of the exhaust and away from himself (and toward the car, of course).

Cross-Draft

Orientation is important for cross draft booths as well. These booths draw air in from the rest of the shop through the filters on the door and exhaust the air through filters at the back of the booth. The painter should again be as far as possible upstream of the surface he is painting.

Why should you use a booth?

To prevent breathing of solvents, coating aerosols, and particularly isocyanates, the spraying of primer, sealer, basecoat, and clearcoat should always be done in a spray booth by a worker wearing respiratory protection.

The booth isolates the more hazardous spraying operations from the less hazardous work being done nearby in the shop. A spray booth supplies clean filtered air to the worker in the booth and removes air contaminated with solvents and paint aerosols to the outdoors. This keeps contaminants from building up inside the booth and also keeps them from reaching and exposing other workers in the shop.

Tips for using a booth

When painting in a booth, it is important to follow a few basic practices to keep your exposure as low as possible.

  • Make sure the booth is operating correctly:
    • Check the air pressure gauge on the control panel - it should agree with the booth manufacturer’s recommendation.
    • Change filters regularly.
  • Before you spray, note the location of the air supply and exhaust vents. Air will flow through the booth between these vents. When spray painting, be sure you are closer to the air supply than the spray gun is - so the overspray will be carried away from you toward the exhaust. It’s a bad idea to spray into the wind!
  • Minimize overspray: 
    • Aim the spray gun perpendicular to the surface being coated and keep a distance of about 6 inches.
    • A laser attachment, called a laser gun training tool, is a great device that helps train new employees [see Specialized Products].
    • The use of a high volume, low pressure (HVLP) spray gun will also minimize overspray.
  • Never remove your respiratory protection or protective equipment until you have left the booth!

Painting outside the booth: While priming should be done inside a spray booth, we know this is not always possible. Priming is often done out on the shop floor which can expose all shop workers to isocyanates and solvents. If priming cannot be done in a booth, do it in a prep station, wearing nitrile gloves and your respirator. Remember, primer contains the same chemicals as the other paints. If priming is done on the shop floor, be sure to warn your co-workers working nearby so that they can wear their respirators, too. Set up the best ventilation you can to keep the paint aerosol and solvent vapors away from yourself and your coworkers and to clear them quickly. Aim the spray gun away from people.

Personal Protective Equipment (PPE)

Spray booths prevent isocyanates and solvents from contaminating the rest of the shop but do not sufficiently protect the painter. Therefore, the painter should wear coveralls (tyvek or nylon) and avoid exposing bare skin to the paint vapor or aerosol. The painter should wear nitrile gloves if the paint contains isocyanates. Most importantly, he must wear a respirator. A supplied air respirator (SAR) is usually recommended but recent evidence shows that cartridge respirators with organic vapor cartridges and pads for overspray, if properly fitted and worn, can also effectively prevent solvent and isocyanate inhalation. Read more…

Isocyanate levels when spraying in different types of booth

The following table shows results from autobody shops which participated in the SPRAY study. We tested the air flow in the booths and tested the air for isocyanates during paint spraying. Some things we noticed were:

  • Crossdraft booths on average had lower air flows, especially the homemade / custom booths. They also had higher air levels of isocyanate than downdraft or semidown draft booths.
  • Prep stations are usually used for smaller jobs so the median isocyanate air level is lower than other booths.
  • Painting outside the booth, on the shop floor, produces lower air levels because the jobs are almost always small (median paint applied was 46 ml vs. 169 ml for inside booths).
  • The last two columns show the percentage of samples that were above the regulatory guidelines for the British Health and Safety Executive (HSE) and the state of Oregon. These results demonstrate why painters should always wear respirators while painting, even in a booth!

Air Exchanges (air changes per minute-acm) and Airborne Isocyanate Concentration by Booth Type

Booth Air Flow (acm)
Air Concentration (ugNCO/m3)
Booth type
Number of booths
Median

25-75th %ile

Number of samples
Median

25-75th %ile

%>70 ugNCO/m3
%>220 ugNCO/m3

Crossdraft (all)

15

0.5

0.3-1.6

36

346

184-705

92

69

Cross draft
homemade

8

0.3

0.2-0.5

20

326

173-705

90

65

Cross draft
prefabricated

7

1.4

0.9-2.3

16

383

224-1060

94

75

Semidown-draft

8

2.0

1.6-2.6

27

271

61.2-563

74

52

Downdraft

17

2.7

2.2-3.4

62

206

81.8-604

81

48

Prep Stations

3

3.0

3.0-11.8

5

185

134 -302

80

40

Outside booth

 

 

 

33

148

34.6-335

67

27

From: Sparer J, Stowe MH, Bello D, Liu Y, Gore RJ, Youngs F, Cullen MR, Redlich CA, Woskie SR. “Isocyanate exposures in autobody shop work: The SPRAY study.” Journal of Occupational and Environmental Hygiene. September 2004: vol.1:page 577.

*Booth diagrams above from: William A. Heitbrink. A Control Matrix for Spray Painting at Autobody Repair Shops. May 1998. US Department of Health and Human Services, Public Health Service Centers for Disease Control and Prevention, National Institute for Occupational Safety and Health, Division of Physical Sciences and Engineering. See the article…