Safety and regulatory overview for powder coating

Editor’s Note: This article is adapted from Michael Streepey, “Safety and Regulatory Guidelines for Powder Recovery Systems & Application Equipment,” presented at FABTECH^®, Nov. 11-13, 2014, Atlanta.

The powder coating process has been popular in the metal manufacturing sector for almost 30 years. Manufacturers can apply the coating efficiently, and the cured coating provides good corrosion protection while also being cosmetically attractive. In addition, because the process doesn’t produce any volatile organic compounds during application, manufacturers look at powder coating as an environmentally friendly finishing technology.

Having said all that, powder coating application and recovery is still a production process, and like anything in a manufacturing facility, safety should always be a top concern. Working with powder may look benign, but it still involves all the elements for potential combustion: the fuel in the form of the powder-to-air mixture from the application gun,

the ignition source that could result from poor grounding of the parts to the rack, and oxygen from the compressed air supply fed into the application booth.

This overview will provide fabricators with the information and tips they need to know to keep their powder coating lines functioning in a safe manner.

Who’s Watching the Manufacturer?

Anyone involved in any aspect of manufacturing knows that regulatory agencies are involved. They are particularly familiar with the Occupational Safety and Health Administration (OSHA), which is dedicated to protecting workers in manufacturing facilities, and the Environmental Protection Agency (EPA), which looks to protect the environment so that individuals can enjoy their surroundings without it adversely affecting their health.

Metal fabricators operating powder coating lines know that they need the appropriate personal protective equipment, such as respirators, for employees who manually apply powder. They also probably realize that powder coating keeps them out of the crosshairs of the EPA because the process doesn’t emit hazardous compounds into the air; in fact, many manufacturers actually reclaim excess powder and reuse it when possible.

But there is also another level of regulatory concerns that some metal fabricators may recognize, but a majority do not. For example, because of the potential fire hazard associated with powder coating, a company installing or operating a line has to ensure that the equipment meets local and state fire marshal expectations. This can prove tricky because individual fire marshal offices often select standards from various agencies to compose fire and workplace safety guidelines for their jurisdictions.

Manufacturers often can find refuge from these inconsistent expections from local officials by following the guidelines set by the National Fire Protection Association (NFPA), an international, nonprofit group with more than 75,000 members from 100 nations. Technical code and standards-development committees regularly meet to create new codes or revise existing codes, all with input from outside parties. All NFPA members then vote on these changes.

In the U.S., the Uniform Fire Code acts as another safety protocol. National Fire Protection codes are established to ensure public safety and fire prevention in and around a building constructed in accordance with the Uniform Building Code.

The American National Standards Institute, on the other hand, focuses more closely on establishing consensus standards that make equipment safe for operation according to the manufacturer’s recommendations. More than 1,000 companies, organizations, and government agencies have input from committees to develop standards that help to ensure end-user safety.

In summary, plenty of organizations have an influence on powder coating line design, installation, and operation. They have a collective heightened sense of safety, and metal fabricators should as well.

The Potential Danger in the Booth

As stated previously, all the elements for a potential fire in a powder booth are there. It is a fact that powder paints are considered to be nonflammable, but in an atomized state—which occurs during application from a gun—they can support a fire.

The conditions that lead to combustion can be hard to recognize. To avoid a potentially dangerous situation, manufacturers need to be vigilant.

For example, grounding of the part being powder-coated to the metal rack has to be complete. This obviously promotes better transfer of the electrostatically charged powder particles to the grounded metal part, but it also prevents a spark from being unleashed.

How does that happen? Ungrounded parts and equipment act as a capacitor when they are subjected to an electrostatic field. After the ungrounded object is saturated with the charge, it discharges the energy to ground, causing an arc or spark. If the arc or spark occurs in an area with the right powder-to-air mixture, the released energy becomes the ignition source that starts a fire.

NFPA 33, Chapter 12.5.2 covers the scenario: “All electrically conductive objects (including personnel) in the spray area, except those objects required by the process to be a high voltage, shall be electrically connected to ground with a resistance of not more than 1 megohm. ”To determine that grounding meets this requirement, powder coaters can use an instrument that applies at least 500 V to the circuit being evaluated; the resulting reading should demonstrate whether or not the ground is acceptable.

One of the best safety tips that can be offered to manufactuers is to regularly clean powder buildup from part fixtures and racks. Too much powder coating on the metal fixture or racks creates a resistance to ground.

Implementing such a cleaning schedule, whether it involves burnoff, blasting, or stripping, eliminates a huge risk of combustion in a powder coating booth—particularly considering that poor grounding is the No. 1 cause of fire in a finishing system.

But sparks can originate in other areas of the booth as well. That’s why NFPA 33, Chapter 12.3 covers hand-held equipment. The code states that the high-voltage circuits of the hand-held apparatus should be designed so that they cannot produce a spark that is capable of igniting the most hazardous powder-air mixture and so that they cannot result in an ignition hazard upon coming in contact with a grounded object under normal operating conditions. The code also adds that the hand-held electrostatic spray apparatus and devices should be listed with a third-party testing laboratory.

The third-party listing from a nationally recognized organization proves that the device has been tested and is approved for use. The organization’s mark then can be found on the device, signifying that it meets the appropriate safety requirements.

(It is noteworthy that “approved” isn’t the same thing as “listed.” NFPA defines “approved” as “acceptable to the authority having jurisdiction,” such as the local fire marshal. It is not the same thing as being listed with a third-party testing laboratory, which actually verifies how the equipment performs against industry standards.)

It makes sense for NFPA to cover equipment for automatic application as well as manual application. NFPA 33, Chapter 9 does just that.

The code is specific that automated powder application equipment (listed and unlisted) should be protected by listed optical flame detection, which in the event of ignition reacts to the presence of flame within 0.5 second. In this instance, conveyors into and out of the area automatically stop, and ventilation, application, transfer, and powder collection equipment turns off. Segregation dampers in ductwork are closed to interrupt airflow from the application equipment to the powder collectors.

Here is one last note that may surprise manufacturers: Sprinklers are required in a powder booth. OSHA requires the automatic sprinklers, and NFPA requires automatic fire suppression (sprinklers are used in most cases) and flame-detection equipment (for automatic systems only) inside booths. Sometimes local regulations go further. For example, Los Angeles requires flame-detection equipment in both manual and automatic systems.

Focusing on Air Movement

The proper airflow is needed to contain the powder air in a booth and minimize the risk for a combustible event. The proper airflow for a booth without inlet ductwork is figured using this equation:

Containment Airflow Required (CFM) =

Total Booth Opening Area (sq. ft.) x Face Velocity (FPM)

The NFPA does not publish minimum air velocity levels for booths without inlet ductwork. An average face velocity of 100 FPM is typically good enough to do the job for most booths. However, higher face velocities are required for tall booth openings greater than 6 ft. (120 FPM); heated parts greater than 120 degrees F (150 FPM); short part hooks less than 24 in. (120 FPM); and quick color change booths (140 FPM).

Regulations are more exact for airflow in booths with inlet ductwork. NFPA 33, Chapter 15 states that where nondeposited, air-suspended powder overspray is coveyed by ductwork to a recovery system, sufficient airflow should be provided to maintain the powder concentration in the ductwork at no more than 50 percent of the minimum explosive concentration (MEC) of the powder in use.

The MEC is not typically available from the manufacturers of powder coatings. If that specification is not available (or if the system is projected for use with a variety of powder coatings), a figure of 30 oz./1,000 ft.3 can be used.

To determine a suitable airflow for this type of powder application system with inlet ductwork, a manufacturer can use the following formula:

Safety Air Volume (CFM) = Maximum Gun Output x # of Guns 0.5 (Safety Factor) x MEC

In most of these booth designs, each gun usually requires 1,000 CFM of containment air when used with a remote after-filter.

So can the collection system influence the possibility for an explosion in a powder coating booth? No and yes.

Open collection systems, such as a cartridge-based design, do not require venting, and MEC requirements do not apply. This type of design has a large opening that prevents pressure from building up during a fire. Powder may burn in this type of collection system, but an explosion will not occur.

Closed collection systems have the potential for an explosion. To prevent this occurrence, these types of spray booths require explosion venting to an area outside the plant or explosion-suppression systems.

NFPA 33, Chapter 15 addresses this. It states that closed collection systems should be listed for the specific application or designed to resist the destructive effects of an internal deflagration. Any enclosure that is not so listed and is effectively “tight,” such as a spray booth, dust collector, powder recovery device, or other enclosure, should be provided with one of the following: deflagration venting or a deflagration suppression system that meets the requirements of NFPA 69, Standard on Explosion Prevention Systems.

A deflagration vent is an opening in an enclosure through which material expands and flows, which helps to relieve pressure. If enclosures with deflagration vents are located inside of buildings, companies are required to use ductwork to vent air from the enclosure to the outdoors. This approach is popular because it is relatively inexpensive, easy to install, and requires little ongoing maintenance. But the big disadvantage of this option is that it does not put out the flame should ignition occur. Flames, pressure, and unburned products will exit through the vent and may cause further damage or injury.

A suppression system immediately addresses the danger in the closed collection system. When combustion occurs, the heat generates pressure. The suppression system detects the pressure buildup and disperses a suppressant agent into the affected area. The flame is quenched, which eliminates any further pressure increase. The flame is contained inside the vessel. The response time for this type of system is in milliseconds.

Cleaning up the Dust

Dust that collects on a manufacturing facility’s floor might be considered normal. It also can be dangerous.

Dust, whether metal or some nonmetallic inorganic material, has the ability to catch fire and explode when mixed with air. These materials may not be considered combustible under normal conditions, but the right combination of particle size, concentration, and presence of an ignition can turn that dust into combustible dust.

NFPA 654, Chapter 6, which covers facility and systems design, states that portions of the process and facility interior where dust accumulations exist external to equipment in sufficient depth (0.0625 in. or 5 percent or more of the floor area) to prevent discerning the underlying surface color should be evaluated to determine if a dust explosion or hazard of flash fire hazard exists. The width of a dime is approximately the same thickness as 0.0625 in.

NFPA 654, Chapter 8 describes acceptable cleaning methods to control dust in a manufacturing facility. Vacuuming is the preferred method.

OSHA has made combustible dust part of its National Emphasis Program (CPL 03-00-008). More information can be found in the agency’s 29 CFR 1910 standard.

Of course, OSHA is just one resource. If a manufacturer has questions about powder coating equipment safety, it should consult local agencies governing fire, plant safety, and environmental requirements or check one of the following publications:

• NFPA 33
• NFPA 68
• NFPA 69
• NFPA 654
• UFC Part V, Article 45