Recent Changes in NFPA 33: Standard for Spray Application Using Flammable or Combustible Materials

Founded in 1896, The National Fire Protection Association (NFPA) is the recognized leader in developing and publishing safety standards. The Chemical Safety Board (CSB) identified 281 combustible dust incidents between 1980 and 2005 that killed 119 workers and injured 718, and extensively damaged industrial facilities.

The CSB found that the National Fire Protection Association (NFPA) has issued comprehensive standards to prevent and mitigate combustible dust explosions; the standards are widely recognized by experts as effective and authoritative. While the NFPA has issued several standards which cover combustible dust, NFPA 33: Standard for Spray Application Using Flammable or Combustible Materials is the standard written specifically for the spray application of powder coatings.

Initially published in 1921 as part of the Standard on Dip Tanks, which later became NFPA 34: Standard for Dipping, Coating, and Printing Processes Using Flammable or Combustible Liquids, NFPA 33 became a separate standard in 1926. As the name implies, NFPA 33 is written for both liquid and powder spray applications. While many system, application, and cure issues are shared between the two technologies, there are some significant differences. In an effort to reduce confusion and to make the standard easier for users, much of the information relating to powder application has been consolidated in Chapter 15.

There have been many revisions to the standard since 1926, each incorporating the latest updates and improvements in the spray finishing industry. Beginning after the 2011 revision of NFPA 33, the Technical Committee began making major changes. Within the Technical Committee, several task groups were formed to concentrate on particular areas of the standard. For the 2016 edition, two significant areas were addressed. The first was to address the growing need to standardize spray applications in membrane enclosures. These enclosures, some large enough to fit ocean going vessels, are made out of a disposable material. Concerns ranging from flammability of the membrane itself to ventilation and fire suppression were addressed. Field trips to installations, testing of membranes, and meeting with other NFPA standards committees were just part of the process of the writing of this new chapter. Presentations by interested parties, public input, and full Technical Committee discussions all came before the final vote to include the new Chapter 18.

Meanwhile, another task group worked on updating the powder application information and the information in the Annex. The ideas for changes began not long after the 2011 edition was published and have been incorporated in the 2016 and 2018 editions. As the powder coating industry continues to expand and technology develops, additional changes will be incorporated into future editions.

Since NFPA 33 is a standard on spray applications of both liquid and powder, it was written on the premise that each chapter would contain the information needed on a particular topic. For example, Chapter 3 is Definitions, Chapter 7 is Ventilation, and Chapter 9 is Protection. That only works as long as there are no differences in how to handle liquid and powder. But there are differences, and not everyone who reads and tries to interpret the standard are coating experts. This standard must be written so it can be understood by what we call Authorities Having Jurisdiction (AHJs). These include fire professionals, building inspectors, insurance agents, and OSHA inspectors, most of whom are not coatings experts. So, beginning with the 2016 edition, the NFPA 33 task group on powder began to revise the information in the standard. There is a great deal of information in the standard which can be shared between liquid and powder applications, and that information has been kept in the individual chapters of the standard. Information specific to powder was moved to Chapter 15 to eliminate confusion when liquid and powder technologies have differences.

While mixing rooms have been addressed in the NFPA 33 standard, rooms or areas where super sacks are stored, or powder dumping occurs were not addressed. In 2016, Chapter 15 was completely revised to incorporate operations such as bag dump stations, pneumatic conveying systems, and other operations that generate dust.

The Annex section of the NFPA standards are not part of the requirements of the standard but are included to provide additional information and explanation. Annex C provides information regarding ventilation and airflow for powder application systems. Included is a table listing combustibility test data of specific powders. The data prior to the 2016 edition was dated and questioned by some as to the accuracy. Epoxy, polyester, and epoxy-polyester hybrid coatings with differing levels of inert ingredients, along with several coatings containing blended and bonded aluminum pigments were tested. These powders verified the previous data and the table was expanded to include minimum explosive concentration (MEC), KSt and Pmax, and auto-ignition temperatures. With thousands of coating powders for sale, it is not reasonable to think all powders have been tested; therefore, Annex C also states: “If that specification (MEC) is not available (or if the system is projected for use with a variety of coating powders), a figure of 30 g/m3 (30 oz./1000 ft3) can be used.” The information included in this table is the type of data requested and used by AHJs and equipment manufactures to provide safe installations of powder equipment.

NFPA 33 changes for powder coating continued in the 2018 edition. Several sections in Chapter 6 – Electrical and Other Sources of Ignition, and many of the figures and diagrams were revised to eliminate any ambiguity from previous editions.

Chapter 9 – Protection, proved to be confusing. For example, in the case of a liquid fire, the exhaust should be kept running, which is just the opposite for a fire in a powder application. To help eliminate the confusion, Section 15.5 – Protection, was added under Chapter 15. A total of 27 items were moved from Chapter 9 and were updated and incorporated into Chapter 15. This information has greatly reduced the confusion between liquid and powder systems and makes the document more usable.

The next revision of the NFPA 33 standard begins when the Technical Committee meets in May. Revisions will be discussed, and task groups will be formed to work on proposed wording. If required, testing will be completed, and data gathered. Drafts will be published for public comment prior to a final draft. The entire process takes two to three years, but in the end, we will have a new and better standard.

The National Fire Protection Association has several standards on combustible dust. Some are written for specific industries or operations, such as NFPA 484: Standard for Combustible Metals, and NFPA 61: Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities. Other standards are more general, such as NFPA 654: Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, and NFPA 652: Standard on the Fundamentals of Combustible Dust. As mentioned earlier in this article, NFPA 33: Standard for Spray Application Using Flammable or Combustible Materials is the standard written specifically for the spray application of powder coatings.

AHJs serve us in an effort to keep our employees and facilities safe. They are not experts in powder coating operations. Not all AHJs use NFPA standards when rendering a decision about a powder application. They may be using a different set of standards, such as the International Fire or Building Code or a local building code. If you run into issues, reach out to your equipment and powder supplier for assistance. Together, they may be able to talk to the AHJ and provide additional information or help educate them on the issue at hand. Each situation is different, and while the discussion does not always result in a decision in your favor, in many cases the education provided is a benefit to all parties involved.

by Martin Korecky, member of the NFPA 33/34 technical committee 
and Chair of the Task Group on powder coating