When is a Woodshop Dust Hazardous?

The F-1 rated building is a multi-activity building which the tasks are scattered from office to design to a basic woodshop. The woodshop is equipped with a vendor design/build dust collector.

This woodshop is designed for only creating certain components of their models and it is used intermittently. Each equipment has manual volume dampers on the dust collection system. Only few of the shop equipment will be functional at any given time.

Background and Code Information
Definition of Dust California Fire Code 2007

California Fire Code 2007 Chapter 13 (Combustible Dust-Producing Operations) defines the combustible dust as: Finely divided solid material which is 420 microns or less in diameter and which, when dispersed in air in the proper proportions, could be ignited by a flame, spark or other source of ignition. Combustible dust will pass through a U.S. No. 40 standard sieve.

Minimum Dust Concentration for Fire/Explosion Hazard
The TruWood Siding/Trim MSDS Wood Dust sheet addresses the unusual Fire and Explosion Hazards as following: “Depending on moisture content and more importantly, particle diameter, wood dust may explode in the presence of an ignition source. An airborne concentration of 40 grams (40,000 mg) of dust per cubic meter of air often used as the LEL for wood dust.

NFPA 70: California Electrical Code 2007
NEC 2005. (C) (1) Class II, Division 1 location is a location
(1) In which combustible dust is in the air under normal operating conditions in quantities sufficient to produce explosive or ignition mixtures, …

OSHA Standards: Electrical Classification
The facility analysis must identify areas requiring special electrical equipment classification due to the presence (or potential presence) of combustible dust. The OSHA Electrical standard (29 CFR Part 1910 Subpart S) contains general requirements for electrical installations in hazardous areas. Detailed requirements for equipment and wiring methods are in NFPA 70, the National Electrical Code®. However, NFPA 70 does not define combustible dusts.
Further guidance on area classification is contained in NFPA 499, Recommended Practice for the Classification of Combustible Dusts and of Hazardous (classified) Locations for Electrical Installations in Chemical Process Areas. This document uses the same definition of combustible dust as NFPA 484 and NFPA 654. The overall dust hazard designation for electrical requirements is Class II. This is further broken down into Divisions which represent the probability of dust being present at any given time. Additionally, each dust is assigned a group (E, F, or G), representing the dust types (metal, carbonaceous, and other, respectively) with different properties. For instance, group E dusts are electrically conductive and electric current can pass through a layer of such dust under favorable circumstances, causing short circuits or arcs.

OSHA Standard: Other Hazard Analysis Considerations
The amount of dust accumulation necessary to cause an explosive concentration can vary greatly. This is because there are so many variables – the particle size of the dust, the method of dispersion, ventilation system modes, air currents, physical barriers, and the volume of the area in which the dust cloud exists or may exist. As a result, simple rules of thumb regarding accumulation (such as writing in the dust or visibility in a dust cloud) can be subjective and misleading. The hazard analysis should be tailored to the specific circumstances in each facility and the full range of variables affecting the hazard.

Many locations need to be considered in an assessment. One obvious place for a dust explosion to initiate is where dust is concentrated. In equipment such as dust collectors, a combustible mixture could be present whenever the equipment is operating. Other locations to consider are those where dust can settle, both in occupied areas and in hidden concealed spaces. A thorough analysis will consider all possible scenarios in which dust can be disbursed, both in the normal process and potential failure modes.

After hazards have been assessed and hazardous locations are identified, one or more of the following prevention, protection and/or mitigation methods may be applied. The references and information sources at the end of this document will assist in the decision process for the methods suitable to specific work sites. Additional guidance and requirements may be available from local or state fire and building code officials as well as OSHA Area or Regional Offices.

Dust Control NFPA 654

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, contains comprehensive guidance on the control of dusts to prevent explosions. The following are some of its recommendations:
 Minimize the escape of dust from process equipment or ventilation systems;
 Use dust collection systems and filters;
 Utilize surfaces that minimize dust accumulation and facilitate cleaning;
 Provide access to all hidden areas to permit inspection;
 Inspect for dust residues in open and hidden areas, at regular intervals;
 Clean dust residues at regular intervals;
 Use cleaning methods that do not generate dust clouds, if ignition sources are present;
 Only use vacuum cleaners approved for dust collection;
 Locate relief valves away from dust hazard areas; and
 Develop and implement a hazardous dust inspection, testing, housekeeping, and control program (preferably in writing with established frequency and methods).
The OSHA ventilation standard, 29 CFR 1910.94, contains ventilation requirements for certain types of operations (such as abrasives, blasting, grinding, or buffing) which involve dusts, including combustible dusts. Additionally, 29 CFR 1910.22(a)(1) requires employers to keep work places and other areas clean, which includes the removal of dust accumulations.

Ignition Control NFPA 654

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, also contains comprehensive guidance on the control of ignition sources to prevent explosions. The following are some of its recommendations:
 Use appropriate electrical equipment and wiring methods;
 Control static electricity, including bonding of equipment to ground;
 Control smoking, open flames, and sparks;
 Control mechanical sparks and friction;
 Use separator devices to remove foreign materials capable of igniting combustibles from process materials;
 Separate heated surfaces from dusts;
 Separate heating systems from dusts;
 Proper use and type of industrial trucks;
 Proper use of cartridge activated tools; and
 Adequately maintain all the above equipment.
The use of proper electrical equipment in hazardous locations is crucial to eliminating a common ignition source. The classification of areas requiring special electrical equipment is discussed in the Facility Dust Hazard Assessment section above. Once these areas have been identified, special Class II wiring methods and equipment (such as “dust ignition-proof” and “dust-tight”) must be used as required by 29 CFR 1910.307 and as detailed in NFPA 70 Article 500. It is important not to confuse Class II equipment with Class I explosion-proof equipment, as Class II addresses dust hazards, while Class I addresses gas, vapor and liquid hazards.

The use of industrial trucks is regulated by OSHA’s Powered Industrial Trucks standard (29 CFR 1910.178). Hazardous atmospheres including dust concentrations are addressed in paragraph (c) of this standard.

Where coal-handling operations may produce a combustible atmosphere from flammable dust, employers covered by the Electric Power Generation, Transmission, and Distribution standard must eliminate or safely control ignition sources. See 29 CFR 1910.269(v)(11)(xii).

Damage Control NFPA 654

NFPA 654, Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids, contains comprehensive guidance to minimize the danger and damage from an explosion. The following are some suggested protection methods:
 Separation of the hazard (isolate with distance);
 Segregation of the hazard (isolate with a barrier);
 Deflagration venting of a building, room, or area;
 Pressure relief venting for equipment;
 Provision of spark/ember detection and extinguishing systems;
 Explosion protection systems (also refer to NFPA 69, Standard on Explosion Prevention Systems);
 Sprinkler systems; and
 The use of other specialized suppression systems.
Training

Employees

Workers are the first line of defense in preventing and mitigating fires and explosions. If the people closest to the source of the hazard are trained to recognize and prevent hazards associated with combustible dust in the plant, they can be instrumental in recognizing unsafe conditions, taking preventative action, and/or alerting management. While OSHA standards require training for certain employees, all employees should be trained in safe work practices applicable to their job tasks, as well as on the overall plant programs for dust control and ignition source control. They should be trained before they start work, periodically to refresh their knowledge, when reassigned, and when hazards or processes change.

Employers with hazardous chemicals (including combustible dusts) in their workplaces are required to comply with 29 CFR 1910.1200, the Hazard Communication standard. This includes having labels on containers of hazardous chemicals, using material safety data sheets, and providing employee training.

Management

A qualified team of managers should be responsible for conducting a facility analysis (or for having one done by qualified outside persons) prior to the introduction of a hazard and for developing a prevention and protection scheme tailored to their operation. Supervisors and managers should be aware of and support the plant dust and ignition control programs. Their training should include identifying how they can encourage the reporting of unsafe practices and facilitate abatement actions.

Analysis

Discussion and Analysis

A. The CEC 2007 requires Classification of the Woodshops if sufficient quantities of dust to induce explosion
B. As per R&D operation, the woodshop is only an R&D shop, the operation is intermittent as support for model group, and intermittent operation.
C. The facility is equipped with Dust Collector and will remove majority of the wood dust from the equipment.
D. As per R&D Shop must provide data: the amount of operation and amount of wood used at the shop will be less than 40 grams in meter cube (0.042 oz per cubic feet) and will not reach the explosion limits as indicated by the MSDS.
E. The most important component of the California Fire Code is “House Cleaning” or OSHA Standards as well as NFPA 654. Daily cleaning and house keeping is mandatory.
F. NFPA 654 standard further describes the activity for Dust Control, Ignition Control, the Damage Control, Training- Employees and Management.
G. The NFPA 654 Guidelines as well as a periodic House Keeping poster must be posted in clear view of the space with 16 point lettering Black on white background.

Conclusion and Recommendation

In conclusion, based on understanding and identifying the maximum level of wood powder density, and all other background and code research, the following conclusion can be achieved.

Based on best management practices and house keeping set forth by NFPA Standards, the level of operation of the shop, the frequency of the operation, and presence of the dust collector machine, the R&D wood shop located may not be rated per California Electrical Code in Class and Divisions.

The motor of the dust collector is not within the stream of the air flow.