Jupiter, FL (PRWEB) July 17, 2008
In 1994, CV Technology, Inc, a global leader in dust explosion protection and consulting, first introduced Quench Tubes to the North American Market. Developed in Europe, these devices have a proven track record of success for the passive protection of small to medium sized vessels inside occupied buildings. They free up floor space as well as offer the option to protect via explosion venting in locations where it is not possible to duct to the outside. They are reliable, require no routine maintenance and in consequence, have grown enormously in popularity during the past decade.
In 1998, the National Fire Protection Association included recommendations for their safe use in the NFPA 68, Guide for Venting of Deflagrations. The guide was revised in 2002, and then in 2007, NFPA 68 became the Standard on Explosion Protection by Deflagration Venting. Through all editions of NFPA 68, the requirements for their safe use have not changed. Paragraph 6.9 of the 2007 Standard is entitled "Venting with Flame Arresting and Particulate Retention." This wording is not ambiguous and makes clear that these devices must arrest flame AND retain dust.
In the past couple of years simpler and much less costly devices have been introduced that operate on the same principle as the quench tubes. The compromise is that these devices must either be much less efficient or more often, they must allow dust to escape through the mesh to function with reasonable efficiency.
So is it alright to allow a flame arresting only device for use inside an occupied building? Or even inside an un-occupied building? Some of these devices have been tested and approved in Europe and have ATEX Certification. Does that make it OK to use them in North America?
The Chairman of the Technical Committee posed this question to the NFPA Staff Liaison, here is his reply:
Dear Mr. Rodgers,
This is in response to your inquiry for clarification of the requirements within NFPA 68, Standard on Explosion Protection by Deflagration Venting (2007 edition), pertaining to venting systems when venting is intended to be located interior to a building.
As paragraph 6.9.1 notes, there are situations where external venting is not feasible, such as when equipment or an enclosure located indoors cannot practically be located adjacent to exterior walls or where the length of vent ducting is too long to be effective. In such cases, the standard recognizes an alternative technology, introduced into NFPA 68 first in the 1998 edition, which was then a guide. This technology is referred to as flame arresting and particulate retention and has been designed with the intent of providing a technology that can be located indoors.
The Committee on Explosion Protection Systems reviewed test data and reports provided as part of the listing for these devices. In all the discussions within the Committee, the devices were considered on the basis that they functioned to both arrest or quench flame and to also retain particulates. The Committee did not discuss any system that was intended to provide either function singly.
So, in response to your question, it is my opinion that paragraph 6.9.1 requires any device intended to satisfy this requirement to do both functions - provide flame arresting and particulate retention. Further, it is my opinion as Staff Liaison to the Committee that any device proposed that only achieves one of the two functions does not meet the intent of this requirement and thus should not be permitted to be used for venting indoors.
This response represents my opinion as Staff Liaison to the Committee and does not represent a formal interpretation of the Committee. It has not been processed through the Committee in accordance with the requirements for a Formal Interpretation. If you have other questions on this document, please contact me.
Guy R. Colonna, P.E.
1 Batterymarch Park
Quincy, MA 02169-7471
gcolonna @ nfpa.org
So the answer is clear that the Committee did not consider a device that would only arrest flame, but not retain dust to be suitable for use indoors. That is where the matter stands today and the use of devices that do not meet both requirements should be viewed as not in compliance with the Standard.
In view of several recent industrial dust explosions where fugitive dust was found to be a major component in these accidents it would seem clear that the Technical Committee insistence on requiring both flame arresting and dust retention was appropriate. There seems little ground for compromise on this critical requirement for safety.