by Ronald L. Allen, MS, PE, CSP, Senior Consulting Engineer, Fauske & Associates, LLC
Requirements, Risks and Incidents Associated With NFPA 652 Direction to Control Combustiblle Dust Hazards. Not all Enclosureless Dust Collectors (EDCs) are intended for combustible dust.
NFPA 652 – 2016, Standard on the Fundamentals of Combustible Dust, defines an enclosureless dust collector (EDC) as, “An air-material separator (AMS) designed to separate the conveying air from the material being conveyed where the filter medium is not enclosed or in a container”. Commodity-specific NFPA standards offer more detailed definitions. EDCs may also be known as Positive Pressure Open Dust Collectors.
Enclosureless dust collectors (EDCs) are commonly used in the woodworking industry and home woodworking shops. They are also present in other varied industries and applications – whether or not such applications are permitted by NFPA standards.
EDCs are available from a breadth of manufacturers. Designs vary considerably – from very simple to complex. Units are available with single or multiple filters (“bags”). Typically, EDCs are less expensive to purchase than traditional cartridge or baghouse style dust collectors. Not all EDCs are intended for combustible dust service. The sketch depicts a multiple filter EDC.
Deflagration Risks Associated with Enclosureless Dust Collectors
Some risks from traditional explosions are reduced with compliant EDCs since creation of projectiles would be limited given the fabric filter bags used in construction. Yet, deflagration and flash fires risks remain as discussed below.
NFPA Requirements for Indoor Use of Enclosureless Dust Collectors
Because of this blog’s space constraints, discussion is limited to indoor, prescriptive requirements for utilization of EDCs. NFPA 652 does not permit EDCs to be located indoors unless the appropriate industry or commodity-specific standards allow such installations. Only NFPA 664 - 2012, Standard for the Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities, and NFPA 654 - 2013, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, allow indoor use of the EDCs. Indoor use of EDCs is not permitted by inference when collecting combustible agricultural dust since they are not referenced in NFPA 61 - 2013, Standard for the Prevention of Fires and Dust Explosions in Agricultural and Food Processing Facilities (Note: performance based design option could be used to justify use of EDCs for some agricultural dusts). NFPA 484-2015, Standard for Combustible Metals) specifically bans the use of EDCs.
NFPA 664 states that explosion protection and isolation requirements do not apply to compliant EDCs and that compliant EDCs are permitted to exhaust into the buildings.
NFPA 654 warns that EDCs are not meant for use with most dusts created during the venting of process equipment or other aerated dust sources. The Standard indicates that fine dust will rapidly blind the filter, which results in reduced performance and a significant increase in deflagration hazards associated with the system operation and performance.
Requirements for indoor usage of EDCs vary somewhat between NFPA 654 and NFPA 664. Common and unique requirements appear below:
While automatic sprinkler protection is not required in EDCs, NFPA 664 recommends protecting EDCs with either an automatic sprinkler located above the unit or a spark detection and extinguishing system in the main duct, upstream of the unit.
C. NFPA 654 Requirements
Incidents Involving Enclosureless Dust Collectors
Deflagrations involving EDCs have been reported, but broad-based data is not readily available. Readers of this blog are encouraged to share their experiences. For more information on this and other Dust Hazard Analysis (DHA), contact Ron Allen at Allen@fauske.com, 608-698-6105 or 630-323-8750
 NFPA 664 allows for indoor locations of EDCs but highly recommends outdoor locations. NFPA 664 advises against locating dust collectors on the roofs of buildings.
 NFPA 664 permits shaking or pressure-pulsing if the fan is off.
 NFPA 654 interpretation: Dust must be removed daily and is limited a maximum of 22 lbs. (10 kg) per day.
 NFPA 654 interpretation: Enclosureless dust collectors are often manifolded into multiple bags (with collected material containers). Each such manifolded assembly must be separated by the required 20 ft. or 6.1 m.)