By Emily Refermat
Whether covered from head to foot in personal protective equipment painting a Cessna Citation in a cross-draft paint booth or wearing gloves and a respirator spraying a wheel in a well-ventilated area of the maintenance hangar, the same safety concerns exist - fire and personal safety.
According to Charles Pritchard and Rich Thelen from Global Finishing Solutions™, fire is public enemy No. 1. The National Fire Protection Association (NFPA) 33 (Standard for Spray Applications Using Flammable or Combustible Materials 2003 Edition) is the paint booth operator's bible. It tells you what you can and can not do in the enclosed area of a paint booth. The NPFA defines safety categories for the paint booth, the interior of which is Class 1 Division 1 which means any electrical device that goes in the booth needs to be rated appropriately from NFPA 70 (NEC) and according to Pritchard, NEMA (National Electrical Manufacturing Association) 7. Electricity is a problem because it introduces a high temperature (a spark) that might ignite the vapors in the booth. For this reason, pneumatic tools are used most often in the paint booth, which not only includes the spray gun and painting apparatus, but also pneumatic climbing/lift equipment.
The NPFA Chemical Hazard Label can, at-a-glance, help you disseminate the threat of the paint you are using. It is that diamond shaped label (see page 20), which has four diamonds inside it, each with a number corresponding to a certain level of toxicity. The top or red corresponds to flammability, blue or left to health, yellow or right to reactivity, and white or bottom to special such as water reactive, oxidizing agent, etc. MSD Sheets will also give you this information in more detail with specifics about product ingredients and identification, health hazards information, flammability information, precautions, transportation, stability/reactivity, etc.
Ventilation is an important step in the fight against fire in a paint booth. Pritchard says the air should be moving "typically 100 feet per minute" to capture the "overspray, airborne particulate" that doesn't stick to the piece being painted. The particulate gets pulled into a "wall of filters" that separates the work area from the exhaust area. Once the air has reached the exhaust chamber it is released back out as reasonably clean air.
Stuart Mack from Sherwin-Williams suggests designing any paint booth for its specific application. That way you can guarantee the airflow and exhaust systems will work effectively.
Besides the particulate from the paint, hydrocarbon solvent vapors more commonly referred to as volatile organic compounds (VOCs) can be an issue for paint booth operators. Pritchard says these vapors are usually only a problem in a large cubic area of exhaust and tend not to be filtered unless they are produced in a high volume or required by local law. He sights California as an example of where VOCs must be filtered out of the air no matter how small the paint booth. To filter VOCs is very expensive. It requires more airflow and two sets of charcoal/carbon filters (two so that when one is saturated it can be sent for cleaning and the other one used). Other systems are also available for large facilities that need to remove VOCs. For example Lockheed Martin's Wisconsin facility uses a centralized VOC abatement system, as Pritchard calls it, that pulls the air from the surrounding paint booths to a central incinerator to burn up VOCs. This high-volume system is quite expensive.
Personal safety generally refers to the use of personal protective equipment (PPE). Here is where the colored diamond NFPA chemical hazard label and MSDS will be invaluable. For the NFPA label it is the blue diamond that signifies health. A rating of 2 requires breathing apparatus and 3 requires full protective clothing. Since the type of PPE depends on the material being used, the labeling of the paint is extremely important. The ratings of hazardous materials can sometimes change, like maintenance manuals, so it may be a good idea to check periodically even if you work with these materials everyday.
Pritchard describes the most common PPE in an aviation spray booth as a "spacesuit," the nickname for Tyvek ® coveralls, gloves, boots, and a full head mask with air hoses for breathing. Mack also stresses the need for positive pressure, especially in the air hose so contaminated air can't get in.
Although there are face masks with various filters for less extensive painting or less toxic products, Mack warns that proper fit is always an issue. Operators with facial hair or with a face that does not conform to the one-size-fits-all mask will be breathing vapor and particulate unless they take other precautions.