Dust Collection System Compatible with NFPA



Summary


In this article, we summarize and contrast the requirements of the National Fire Protection Association’s (NFPA) Standards 664 and 652 for on-demand dust collection control systems (generally - industrial exhaust ventilation systems).


A properly designed, installed, and calibrated Ecogate System fulfills NFPA 664 and NFPA 652 requirements for control systems (these standards are very complex, and requirements for control systems are only a very small part of the standards). Ecogate systems measure and regulate minimum air volume as well as minimum air velocity in the entire duct system which is a critical part of these standards.



NFPA 664 | NFPA 652


Please note that pressure regulated control systems (usually a pressure transmitter connected to the Variable Frequency Drive and set to regulate constant pressure in the main duct) cannot by itself fulfill NFPA 664 or 652 because they are regulating exclusively pressure, not air velocity and/or air volume.


An extreme example: If you will blank off the main duct, the pressure regulated system will happily regulate to set pressure, but there is no airflow, no minimum transport velocity. Technically put, the system is on the left side of the fan curve with no airflow at all.

As you probably know, according to the National Fire Protection Association’s Standard on the Fundamentals of Combustible Dust (NFPA 652), industrial facilities that handle combustible dust must have completed Dust Hazard Analyses (DHAs) by September 7, 2020. You can view these standards for free (just create an account) online at nfpa.org.


The NFPA standards become a law when they are included and referenced in an adopted code and/or are adopted on their own by a municipal jurisdiction. A code is a model and a set of rules that knowledgeable people recommend for others to follow. It is not a law but can be adopted into law. You can check if at your location these standards are adopted with your Authority Having Jurisdiction (AHJ). Another option is to check online at www.nfpa.org/Codes-andStandards and use “CodeFinder”. Some states, for example, Washington, extended NFPA 652 code effective date to February 1, 2021.


Listed below are ten different requirements of NFPA-664 and NFPA-652 for dust collection systems (design, specification of air volumes, system capacity, monitoring airflow, use of manually controlled gates, system start, system stop, maintaining minimum transport air velocities, warnings, and system design changes).


#1 Dust collection system design

NFPA-664-20

8.2.2.3.1.6 Where dumpers or gates are used for individual equipment, the volume, and velocity resulting from the operation of such dampers or gates must not reduce the system velocity below the design minimum. 8.2.2.5 Fans or Blowers shall be of appropriate type and sufficient capacity to maintain the required rate of airflow in all parts of the system.

NFPA-652-19

A.9.3.3.3 Systems with Variable-Speed Fans: For use as an add-on to existing dust collection systems, the duct system should be redesigned to comply with the requirements of this section. At full use, the smaller main ducts can produce significant pressure drops, therefore the fan should be sized appropriately to accommodate both minimum and maximum use conditions.


#2 Specification of required air volume for each point of use & dust collector, requirements to design system maintain minimum source point airflow

NFPA-664-20

8.2.2.1.4 Every section of the dust collecting system must be sized for not less than the minimum air velocity and volume required to collect and transport the material through the ducting and into collection equipment. 8.2.2.6 Dust Collectors. The system shall be provided with collection equipment size and capacity to maintain the required airflow and efficiently separate the wood dust from the air before the air is exhausted.

8.2.2.4.2 At each collection point, the system shall be designed to achieve the minimum velocity required for capture, control, and containment of the dust source. The minimum air volume should be documented (8.2.2.4.3).

NFPA-652-19

(1) The required air volume for each point of use and minimum velocity for each branch line and duct section between the points of use and the AMS (dust collector) should be specified. A.9.3.3.3.1: Proper dust collection design requires that a minimum air volume flow be maintained for each dust collection source point (hood). A.9.3.3.3.2: hood minimum design value must be documented to allow field-testing.


#3 System capacity

NFPA-664-20

8.2.2.3.1.5 A: The capacity of the system must be calculated on basis of all hoods and other openings connected to the system being open or equipped with means to ensure minimum convening velocity of 8.2.2.2.1.4 (Every section of the dust collecting system must be sized for not less than the minimum air velocity and volume required to collect and transport the material through the ducting and into collection equipment) in all sections of the system. 8.2.2.3.1.5 B: Floor Sweeps that are normally closed and opened only occasionally are excluded from airflow calculations for the system.

NFPA-652-19

(6) The fan package and AMS (dust collector) used in the system should be compatible with the full performance requirements of the system (all sources open to minimum sources open). Improper selection of these items can result in failure to maintain the required duct velocities.


#4 Monitoring minimum airflow at each drop/branch

NFPA-664-20

Not addressed.

NFPA-652-19

(2) Monitoring should be provided at each drop/branch to assure minimum design airflow is maintained when the branch is open. Also addressed in A.9.3.3.3.2: minimum design airflow value must be documented to allow field-testing.


#5 Use of manually controlled gates

NFPA-664-20

8.2.2.1.3 Once system airflow has been properly balanced, additional pickup points, duct modifications, and modifications of balancing damper settings shall not be made without ensuring that the remaining portions of the system still have sufficient capture and conveying air velocities for their intended function.

NFPA-652-19

A.9.3.3.3 Use of manual slide or “blast” gates is not recommended because it can lead to uncontrolled modification of the flow volumes for both a single line and the system as a whole and result in the improper balance as described above. Proper design methods inherently ensure minimum airflows and duct velocities without the use of manual slide or blast gates.


#6 System start NFPA-664-20

8.2.2.2.2 Startup: Pneumatic conveying, dust collection and centralized vacuum cleaning systems must be designed that on startup the system achieves and maintains design air velocity prior to the admission of material to the system.

NFPA-652-19

(5) All gates should be open at startup.


#7 System stop

NFPA-664-20

8.2.2.2.3.1 Pneumatic conveying, dust collection, and centralized vacuum cleaning systems must be designed that on a normal shutdown of the process the system maintains design air velocity until the material is purged from the system (does not apply during an emergency).

NFPA-652-19

Not addressed.


#8 Maintaining transport air velocities in the entire duct system

NFPA-664-20

8.2.2.4.2 At each collection point, the system shall be designed to achieve the minimum velocity required for capture, control, and containment of the dust source. The minimum air volume should be documented (8.2.2.4.3).

NFPA-652-19

(3) The design should ensure that the required velocity is maintained in all open branches and all duct sections under all use conditions. (4) The controller should automatically open additional points of use or balance air dampers as necessary to always maintain minimum air velocity in all sub-branches and the main duct.


#9 Warning when a system fails to provide the required performance

NFPA-664-20

Not addressed.

NFPA-652-19

(7) Alarms should be provided to alert the appropriate personnel when the system fails to provide the required performance.


#10 Changes of dust collection systems (branch line disconnected, blanked off, etc.), installation of additional branch lines for additional dust sources

NFPA-664-20

8.2.2.1.3 Once system airflow has been properly balanced additional pickup points, duct modifications, and modifications of balancing damper settings shall not be made without ensuring that the remaining portions of the system still have sufficient capture and conveying air velocities for their intended function.

NFPA-652-19

A.9.3.3.3.3: When a branch line is disconnected, blanked off, or otherwise modified it changes the airflows in all the other branches of the system. It can lead to an imbalance of airflows that result in flows below the minimum required. The use of manual gates is not recommended.

A.9.3.3.3.4: Installation of branch lines for additional dust sources to an existing dust collection system will result in lower air volumes and duct velocities for existing portions of the system.



Notes


The latest revisions are NFPA 664-2020 and NFPA-664-2019.


A.9.3.3.3 Systems with Variable-Speed Fans

For use as an add-on to existing dust collection systems, the duct system should be redesigned to comply with the requirements of this section. At full use, the smaller main ducts can produce significant pressure drops, therefore the fan should be sized appropriately to accommodate both minimum and maximum use conditions. The design should include the following elements, at a minimum:


(1) The required air volume for each point of use and minimum velocity for each branch line and duct section between the points of use and the AMS (dust collector) should be specified.


(2) Monitoring should be provided at each drop/branch to assure minimum design airflow is maintained when the branch is open.


(3) The design should ensure that the required velocity is maintained in all open branches and all duct sections under all use conditions.


(4) The controller should automatically open additional points of use or balance air dampers as necessary to always maintain minimum air velocity in all sub-branches and the main duct.


(5) All gates should be open at startup.


(6) The fan package and AMS (dust collector) used in the system should be compatible with the full performance requirements of the system (all sources open to minimum sources open). Improper selection of these items can result in failure to maintain the required duct velocities.


(7) Alarms should be provided to alert the appropriate personnel when the system fails to provide the required performance.



If you have any additional questions regarding how exactly these requirements are addressed in the Ecogate Systems please contact us. This might be addressed in a future article.



Author: Ales Litomisky

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