Division of Labor and Industry


MOSH Instruction 08-05 - Maryland Occupational Safety and Health (MOSH)

Subject: National Emphasis Program (NEP) Combustible Dust
Effective Date: June 18, 2008
Issuance Date: August 7, 2008
Cancellation: MOSH Instruction 07-9
Purpose: This instruction provides notice of and instructions for MOSH’s participation in OSHA’s revised Enhanced Enforcement Program (EEP).
Scope: This instruction applies MOSH-wide
References: OSHA Directive CPL 03-00-008
See Appendix F for other references
(NOTE: CPL 03-00-008 is a new OSHA directive replacing the previously issued directive, OSHA Instruction CPL 03-00-006 issued on October 18, 2007, which described the policies and procedures regarding inspection of facilities that handle combustible dust. The directive does not replace the grain handling facility directive, OSHA Instruction CPL 02-01-004, Inspection of Grain Handling Facilities, 29 CFR 1910.272. In addition, the directive is not intended for inspections of explosives and pyrotechnics manufacturing facilities covered by the Process Safety Management (PSM) standard (1910.119). However, it does not exclude facilities that manufacture or handle other types of combustible dusts (such as ammonium perchlorate) covered under the PSM standard.)
Contact: Chief of MOSH Compliance Services
312 Marshall Avenue, Room 602
Laurel, Maryland 20707
(410) 880-4886 x312
By and Under the Authority of: Roger Campbell, Assistant Commissioner


OSHA reissued the directive on the Combustible Dust National Emphasis Program to increase its enforcement activities and to focus on specific industry groups that have experienced either frequent combustible dusts incidents or combustible dust incidents with catastrophic consequences. OSHA initiated its previous Combustible Dust National Emphasis Program on October18, 2007. As a result of a recent catastrophic accident involving a combustible dust explosion at sugar refinery, OSHA decided to intensify its focus on this hazard. The Agency will increase its activities in outreach, training, the creation and dissemination of guidance and educational materials and cooperative ventures with stakeholders as well as enhancing its enforcement activities through this amendment to the National Emphasis Program.

While MOSH is not initiating a state emphasis program on combustible dust, MOSH will participate in OSHA's Combustible Dust National Emphasis Program.

The purpose of this NEP is to inspect facilities that generate or handle combustible dusts which pose a deflagration or other fire hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape; deflagrations can lead to explosions. Combustible dusts are often either organic or metal dusts that are finely ground into very small particles, fibers, fines, chips, chunks, flakes, or a small mixture of these. Types of dusts include, but are not limited to: metal dust, such as aluminum and magnesium; wood dust; plastic dust; biosolids; organic dust, such as sugar, paper, soap, and dried blood; and dusts from certain textiles. Some industries that handle combustible dusts include: agriculture, chemicals, textiles, forest and furniture products, wastewater treatment, metal processing, paper products, pharmaceuticals, and recycling operations (metal, paper, and plastic).

In situations where the facility being inspected is not a grain handling facility, the lab results indicate that the dust is combustible, and the combustible dust accumulations not contained within dust control systems or other containers, such as storage bins, are extensive enough to pose a deflagration, explosion, or other fire hazard, then citations under 29 CFR 1910.22 (housekeeping) or, where appropriate, 29 CFR 1910.176(c) (housekeeping in storage areas) may generally be issued. Combustible dusts found in grain handling facilities are covered by 29 CFR 1910.272.

For workplaces not covered by 1910.272, but where combustible dust hazards exist within dust control systems or other containers, citations under Labor and Employment Article 5-104(a) (the General Duty Clause) may generally be issued for deflagration, other fire, or explosion hazards. National Fire Protection Association (NFPA) standards (listed in Appendix A of this directive) should be consulted to obtain evidence of hazard recognition and feasible abatement methods.

Other standards are applicable to the combustible dust hazard. For example, if the workplace has a Class II location, then citations under 29 CFR 1910.307 may be issued to those employers having electrical equipment not meeting the standard's requirements.


  1. MOSH compliance and consultation supervisors shall ensure that staff is made aware of the changes and trained on the contents of this instruction.
  2. The Assistant Commissioner or authorized representative shall ensure compliance with the attached guidelines for enforcement.

cc: J. Ronald DeJuliis, Commissioner, Division of Labor and Industry
Craig D. Lowry, Deputy Commissioner, Division of Labor and Industry
Jonathan R. Krasnoff, Deputy Counsel, Department of Labor, Licensing and Regulation
Office of Administrative Hearings


I. Definitions.

The following is a partial listing of definitions based on NFPA standards and 29 CFR 1910.399, the definitions provision of Subpart S-Electrical, that relate to combustible dust.

A. Class II locations. Class II locations are those that are hazardous because of the presence of combustible dust. The following are Class II locations where the combustible dust atmospheres are present:

Group E. Atmospheres containing combustible metal dusts, including aluminum, magnesium, and their commercial alloys, and other combustible dusts whose particle size, abrasiveness, and conductivity present similar hazards in the use of electrical equipment.

Group F. Atmospheres containing combustible carbonaceous dusts that have more than 8 percent total entrapped volatiles (see ASTM D 3175, Standard Test Method for Volatile Matter in the Analysis Sample of Coal and Coke, for coal and coke dusts) or that have been sensitized by other materials so that they present an explosion hazard. Coal, carbon black, charcoal, and coke dusts are examples of carbonaceous dusts.

Group G. Atmospheres containing other combustible dusts including flour, grain, wood flour, plastic and chemicals.

B. Combustible dust. A combustible particulate solid that presents a fire or deflagration hazard when suspended in air or some other oxidizing medium over a range of concentrations, regardless of particle size or shape.

C. Combustible Particulate Solid. Any combustible solid material composed of distinct particles or pieces, regardless of size, shape, or chemical composition.

D. Hybrid Mixture. A mixture of a flammable gas with either a combustible dust or a combustible mist.

E. Deflagration. Propagation of a combustion zone at a speed that is less than the speed of sound in the un-reacted medium.

F. Deflagration Isolation. A method employing equipment and procedures that interrupts the propagation of a deflagration of a flame front, past a predetermined point.

G. Deflagration Suppression. The technique of detecting and arresting combustion in a confined space while the combustion is still in its incipient stage, thus preventing the development of pressures that could result in an explosion.

Detonation. Propagation of a combustion zone at a velocity that is greater than the speed of sound in the un-reacted medium.

H. Dust-ignition proof. Equipment enclosed in a manner that excludes dusts and does not permit arcs, sparks, or heat otherwise generated or liberated inside of the enclosure to cause ignition of exterior accumulations or atmospheric suspensions of a specified dust on or in the vicinity of the enclosure.

I. Dusttight. Enclosures constructed so that dust will not enter under specified test conditions.

J. i The bursting or rupture of an enclosure or a container due to the development of internal pressure from deflagration.

K. Minimum Explosible Concentration (MEC). The minimum concentration of combustible dust suspended in air, measured in mass per unit volume that will support a deflagration.

II. Program Procedures:

A. Inspection Scheduling. Inspections conducted under this NEP will focus on general industry facilities where employees may be exposed to potential combustible dust hazards.

1. Using the most recently available Harris Directory employer list, the Chief of Compliance or designee will prepare a list (based on random number table (RNT)) of establishments in the SICs/NAICS codes in Appendices
D-1 and D-2 of this instruction [which list industries with an OSHA inspection history of combustible dust hazards]. Each establishment on the resulting establishment list will be assigned a sequential number, starting at the top of the list with number one. The Chief of Compliance or designee will then provide to each region a list of establishments in these SICs/NAICS codes within the Regional office's geographical jurisdiction.

2. Based on its familiarity with local industries, Regional Supervisors in conjunction with the Chief of Compliance or designee may then make appropriate additions and deletions to its list, (see Chapter 3 of the MOSH Field Operations Manual (FOM)).

  • Other facilities with a known pattern of combustible dust hazards (with SICs/NAICS other than the ones listed in Appendices D-1 and D-2) may be added, in alphabetical order, to the bottom of the list. The Regional Office shall document the basis for any such addition.
  • The Chief of Compliance or designee shall delete from the master list any facilities not likely to have combustible dust hazards, documenting the basis for such determinations.
  • The Chief of Compliance or designee, in conjunction with the Regional Supervisor, shall delete from the master list any establishments known to be out of business, documenting the basis for such determinations.
  • The Chief of Compliance or designee, in conjunction with the Regional Supervisor, may delete any establishment that has received an inspection addressing combustible dust hazards within the previous five Fiscal Years, provided either that no citations were issued for combustible dust hazards or that a citation(s) was issued but a follow-up inspection documented tangible appropriate and effective efforts to abate the serious hazards cited or MOSH received abatement verification that the dust hazards have been abated. An establishment with a pending contest of a citation related to combustible dust hazards will not be deleted, but the inspection will be deferred during the contest.

3. If additions and deletions are made, each establishment on the resulting establishment list will be assigned a sequential number, starting at the top of the list with number one. A random number table (RNT) (see Chapter 3 of the MOSH Field Operations Manual (FOM)), will then be applied.

4. MOSH shall conduct at least ten (10) NEP inspections from the list of establishments in the SICs/NAICS codes contained in Appendix D-1 and one NEP inspection from the list of establishments in the SICs/NAICS codes contained in Appendix D-2, in each Fiscal Year. Inspections will be scheduled in the order called for by the RNT.

5. Regional Offices will ensure that they schedule and conduct enforcement activities following the guidelines set forth in MOSH Instruction 98-3 Enforcement Exemptions and Limitations Placed on MOSH Activities by the Federal Labor/Health and Human Services Appropriations Act, using the NAICS codes found in the current Appendix, (see MOSH Instruction 07-12).

6. The establishment list generated under this NEP must be maintained by the Chief of Compliance or designee for a period of three years.

B. Scheduling and Resource Allocation.

1. Some establishments selected for inspection under this NEP also may be selected under the current Site-Specific Targeting (SST) Plan. Whenever possible, NEP inspections should be conducted concurrently with SST inspections. If this is not possible, the SST plan inspections have priority and are to be conducted prior to NEP inspections. Refer to MOSH Instruction 07-01, Site-Specific Targeting 2007 (SST-07), or subsequent implementing directive for later years.

2. If a formal complaint or referral is received related to a facility handling combustible dust, the complaint or referral item(s) shall be investigated in accordance with Chapter 3 of the Field Operations Manual (FOM) and an inspection as required by this NEP should be conducted if the Designated Assistant Chief determines that the facility has not already been inspected as per this instruction and resources are available to conduct the NEP inspection.

3. If a nonformal complaint is received related to a facility handling combustible dust, and if an inspection is conducted to investigate the complaint based on the criteria contained in Chapter 3 of the Field Operations Manual (FOM) then an inspection as required by this NEP should be conducted if the Designated Assistant Chief determines that the facility has not already been inspected as per this instruction and resources are available to conduct the NEP inspection.

4. Responses to accidents and catastrophes at facilities handling combustible dust shall follow the guidelines in Chapter 3 of the Field Operations Manual (FOM) and an inspection as required by this NEP should be conducted.

C. Opening Conference.

During the opening conference and after a preliminary walkaround of the facility, if the CSHO determines that the employer's operation does not have combustible dust explosion, deflagration, or other fire hazards, then the CSHO may terminate the inspection, or contact the Regional Supervisor on whether to continue the inspection. Additionally, if the CSHO determines that the facility has undergone a MOSH consultation visit in the past three years and verifies (through a basic walkaround and evaluation of any changes made by the employer) that the combustible dust explosion hazards have sufficiently been addressed by the employer, then the CSHO shall normally terminate the inspection.

During the opening conference, if the CSHO determines that the facility being inspected is covered under the grain handling standard (1910.272), then the CSHO shall not use the guidance provided in this instruction, but instead, shall use the guidance provided in OSHA Instruction, CPL 02-01-004, Inspection of Grain Handling Facilities, 29 CFR 1910.272, November 8, 1996.

D. Inspection Resources.

1. When possible, only CSHOs trained in recognizing the hazards associated with combustible dust shall be assigned to conduct inspections under this NEP. A training course offered by the OSHA Training Institute (OTI) in recognizing combustible dust explosion hazards may be one source of such training. The training at OTI covers various topics, including engineering controls and methodologies in preventing combustible dust deflagration, other fire, and explosion hazards. In addition the training covers several NFPA documents referenced in Section III of this directive, including NFPA 654, NFPA 68, and NFPA 69. (Note: CSHOs knowledgeable in recognition and control of combustible dust hazards and familiar with NFPA provisions need not undergo the training at OTI). The Designated Assistant Chief will ensure that an appropriate number of CSHOs trained in combustible dust hazard recognition are available for inspections under this NEP.

2. If appropriate, the Regional Supervisor in coordination with the Chief of Compliance or designee shall decide as soon as practicable whether or not expert services from outside MOSH (such as expert witnesses) will be needed to support a combustible dust case properly. If so, such services shall be requested from the Chief of Compliance at the earliest date practical.

3. To support inspections under this NEP, the MOSH library shall have industry reference documents available for CSHOs to use as a resource to support research and enforcement activities during the inspection.

Note: Related NFPA documents are available online in readable format, without charge.

At the above web address, the following steps will allow accessing a NFPA standard only in readable format: 1) select the standard, 2) click "Preview this Document", 3) agree to the disclaimer, and 4) open the standard.

4. CSHOs' Safety and Health.

CSHOs shall take appropriate precautionary measures for the particular hazards presented in facilities with combustible dust hazards.

a. Personal Protective Equipment (PPE): In addition to the normally required personal protective equipment, CSHOs shall wear non-spark-producing clothing such as natural fiber (e.g., cotton). It is also recommended that CSHOs be provided with flame-resistant clothing as appropriate.

b. Equipment: Cameras and video cameras shall be appropriate (for example, intrinsically safe) for the work environment. However, if such cameras are not available, then CSHOs shall take photographs or videos (using a telephoto feature) from locations within the plant that are not hazardous (classified) locations. Additionally, CSHOs shall take written statements from employees, and if possible from employers, regarding the hazardous conditions, including the alleged violative conditions (such as dust accumulations over 1/32 inch, explosion vents not directed to safe locations away from the employees working in the area, etc.).

c. Use safe practices when collecting samples, such as not generating a dust cloud while collecting a sample and using the right tools in collecting the samples. Additionally, if a means of safe access is not available, sample(s) should not be collected.

d. Equipment for collecting dust samples may include the following:

  • Natural bristle hand brushes for collecting settled dust.
  • Non-sparking, conductive dust pans (aluminum), for collecting settled dust.
  • Non-spark producing sample container.
  • Non-spark producing funnel for filling sample containers.
  • Non-spark producing scoops for removing dust from cyclone containers or other ventilation equipment.

e. Care shall be taken to ensure integrity of the sample.

E. Inspection and Citation Procedures

1. CSHOs should recognize that the following criteria must be met before a deflagration can occur:

a. The dust has to be combustible.

b. The dust has to be dispersed in air or another oxidant, and the concentration of this dispersed dust is at or above the minimum explosible concentration (MEC).

c. There is an ignition source, such as an electrostatic discharge, spark, glowing ember, hot surface, friction heat, or a flame that can ignite the dispersed combustible mixture that is at or above the MEC.

2. CSHOs should recognize that the following criteria must be met before an explosion can occur:

a. The above criteria for deflagration must be present.

b. The combustible mixture is dispersed within a confined enclosure (and the confined enclosure does not contain sufficient deflagration venting capacity to safely release the pressures) such as a vessel, storage bin, ductwork, room or building. It must be noted that a small deflagration can disturb and suspend the combustible dust, which could then serve as the fuel for a secondary (and often more damaging) deflagration or explosion.

3. CSHOs should be able to recognize the following conditions that may indicate that a potential dust deflagration, other fire, or explosion hazard exists:

a. Plant History of Fires: The plant has a history of fires involving combustible dusts.

b. Material Safety Data Sheets (MSDS): The MSDS may indicate that a particular dust is combustible and can cause explosions, deflagrations, or other fires. However, do not use MSDSs as a sole source of information because this information is often excluded from MSDSs.

c. Dust Accumulations: Annex D of NFPA 654 contains guidance on dust layer characterization and precautions. It indicates that immediate cleaning is warranted whenever a dust layer of 1/32- inch thickness accumulates over a surface area of at least 5% of the floor area of the facility or any given room. The 5% factor should not be used if the floor area exceeds 20,000 ft2, in which case a 1,000 ft2 layer of dust is the upper limit. Accumulations on overhead beams, joists, ducts, the tops of equipment, and other surfaces should be included when determining the dust coverage area. Even vertical surfaces should be included if the dust is adhering to them. Rough calculations show that the available surface area of bar joists is approximately 5 % of the floor area and the equivalent surface area for steel beams can be as high as 10%. The material in Annex D is an idealized approach based on certain assumptions, including uniformity of the dust layer covering the surfaces, a bulk density of 75 lb/ ft3, a dust concentration of 0.35 oz/ ft 3, and a dust cloud height of 10 ft. Additionally, FM Data Sheet 7-76 contains a formula to determine the dust thickness that may create an explosion hazard in a room, when some of these variables differ.

d. CSHOs should observe areas of the plant for accumulations of hazardous levels of dust (for example, greater than 1/32 of an inch, which is approximately equal to the thickness of a typical paper clip. Likely areas of dust accumulations within a plant are:

  • structural members
  • conduit and pipe racks
  • cable trays
  • floors
  • above ceiling
  • on and aroundequipment (leaks around dust collectors and ductwork.)

e. If CSHOs find that there are potential combustible dust hazards, dust samples must be safely collected. CSHOs shall use means of access to upper levels of a facility only when this can be done safely. Dust samples shall be submitted to OSHA's Salt Lake Technical Center (SLTC) for analysis. Locations from which to collect separate samples:

  • "High spaces" such as roof beams, open web beams, tops of pipes and ductwork, and other horizontal surfaces located as high in the overhead as possible. Note: These are the preferred locations; however, if a means of safe access is not available, sample(s) should not be collected.
  • Equipment and floors where dust has accumulated.
  • The interior (i.e., bins and/or bags) of a dust collector.
  • Within ductwork.

4. SLTC Tests. The following are a series of tests which may be performed at SLTC to determine the explosibility and combustibility parameters of the dust samples submitted.
Details on these tests are found in Appendix F.

  • Percent through 40 mesh
  • Percent moisture content
  • Percent combustible material
  • Percent combustible dust
  • Metal dusts will include resistivity
  • Minimum explosive concentration (MEC)
  • Minimum ignition energy (MIE)
  • Class II test
  • Sample weight
  • Maximum normalized rate of pressure rise (dP/dt) - Kst Test
  • Minimum ignition temperature

5. Sampling & Analytical Methods.

  • Air sampling is not necessary.
  • Bulk samples in 1-liter plastic bottles are preferred, because several tests are conducted at SLTC. Obtain samples from several locations so that the amount can be collected in a 1-liter plastic bottle. These bottles may be obtained from the SLTC or locally purchased.
  • Affix an official sample identification seal (OSHA 21) on the container. To seal the bottle correctly apply one end of the seal to the center of the lid. Then run the seal to the edge of the lid and as far down the side of the bottle as it will reach.
  • It is preferred that these sample materials not be collected in plastic bags because they cannot be sealed tightly enough to prevent sample leakage or moisture loss. Also, these bags have a bellows effect which can make the dust airborne when handling the samples.
  • CSHOs should take precautions not to contaminate the sample material. The presence of some contaminants in a sample may result in the tests' underreporting of the explosiveness of the dust being handled at the facility.
  • Document the description of the operation in block 18 of the OSHA 91A form, and indicate the tests to be done on block 30 of the OSHA 91A as follows:
    • When requesting analyses for fire or explosion hazards that may result from housekeeping or L&E Article 5-104(a) violations, write Kst.
    • When requesting analyses for Class II hazardous locations, write "Potential Class II Dust". This test must be done to support a citation for Class II hazardous (classified) locations, 1910.307. (Note: This test only applies to electrical ignition sources in Class II locations.)
  • Because of the resource intensive nature of the tests, MOSH requires the Assistance Chiefs (Health) approval for all combustibility and explosibility testing.
  • Place the prepared materials and required identification papers (including an MSDS) in a box, and ship them to SLTC, following the shipping instructions provided by the shipping company or the U.S. Postal Service. (Note: Normally, no special DOT shipping requirements apply; however, when shipping metal dusts (especially when dusts involve aluminum or magnesium), CSHOs should verify with the shipping company whether any special shipping requirements apply.)

6. Lab results. Lab results may contain some of the results listed below, but not all, depending on particular tests that are performed:

  • Mesh size
  • Moisture content
  • Percent combustible dust
  • Sample weight
  • Explosion severity
  • Kst Value
  • MEC
  • Resistivity for metal dusts

7. Dust collectors, ductwork, and other containers. CSHOs should also pay attention to the dust collectors and ductwork, as well as other containers, because they maintain a cloud of finely divided particles suspended in air. Because they maintain a cloud of combustible dust, CSHOs should determine whether the plant has a sound ignition control program that prevents introduction of ignition sources (including sparks from electrostatic discharge, open flames, or other similar sources) into them. Additionally, housekeeping problems may be exacerbated by the inefficient operation of dust collectors. As noted in NFPA 654, Annex D.2, dust collectors generally operate most effectively between limited pressure drops of between 3 inches to 5 inches of water. If the employer does not have a hot work permit system that addresses hot work on and around collection points and ductwork or in areas where hazardous levels of dust accumulations may occur, the CSHO should recommend that such a system be adopted expeditiously and rigorously implemented. In L&E Article 5-104(a) cases a hot work permit system may be noted as a feasible abatement method. For chemicals covered by 29 CFR 1910.119 (PSM), the standard requires a hot work permit system. See 29 CFR 1910.119(k).

8. CSHOs must gather information about the employer's efforts to abate the combustible dust hazard. This information will be helpful in determining some violations, as well as the employer's good faith, and a penalty factor. CSHOs should look at dust collectors, ductwork, associated equipment, and containers, like mixers or storage bins. The following information may be gathered during the course of the inspection:

  • Explosion prevention and mitigation controls such as the isolation or segregation of dust-generating processes, building damage-limiting construction, explosion venting for dust-processing areas; process equipment relief (see NFPA 68), and process isolation and explosion suppression (see NFPA 69).
  • The dimensions of the room as well as the areas of the dust accumulations of greater than 1/32-inch depth.
  • The design information on the dust collection systems, along with model numbers and serial numbers (located on the side of the equipment along with the manufacturer and phone numbers).
  • Size (volume) of dust collectors (Note: Dust collectors are referred to as "air-material separators" in NFPA 654).
  • Warning signs or alerts on the equipment referencing combustible dust.
  • Any sources of ignition in the area, such as welding, fork truck traffic, etc.
  • Information on whether the electrical equipment in the area is designed for use in a hazardous (classified) location. (Note: Do not open electrical boxes or disconnect electrical cords. Opening them could cause an electrical arc, especially in an area with metal dust.)

NOTE: Because of its spark-producing potential, no equipment, including cameras with electronic flashes or electrical equipment, shall be used in hazardous (classified) locations of the facilities, unless the equipment is intrinsically safe, approved, or safe, as defined in 29 CFR 1910.307(c), for use in these types of areas.

9. Citations.

a. Grain Handling Standard Violations. For violations at grain handling facilities (e.g., flour mills), citations under 1910.272 shall be issued. (See OSHA Instruction CPL 02-01-004, Inspection of Grain Handling Facilities, 29 CFR 1910.272).

b. Ventilation Standard Violations. If the facility's operations are covered by 1910.94, Ventilation, then any violations of the standard shall be cited. Paragraph (a) of the standard covers abrasive blasting; paragraph (b), grinding, polishing, and buffing operations;

c. Housekeeping Violations. If the facility being inspected under this NEP is not a grain handling facility, and the surface dust accumulations (i.e., dust accumulations outside the dust collection system or other containers, such as mixers) can create an explosion, deflagration or other fire hazard, then citations for violations of 29 CFR 1910.22 (housekeeping) shall be issued. The standard provides in pertinent part: "(a) Housekeeping. (1) All places of employment, passageways … and service rooms shall be kept clean… (2) The floor of every workroom shall be maintained in a clean…condition." Courts of appeals and the Occupational Safety and Health Review Commission have held that 1910.22 applies to the hazard of combustible dust. Con Agra, Inc. v. OSHRC, 672 F.2d 699 (8th Cir. 1982); Bunge Corp. v. Secretary of Labor, 638 F.2d 831 (5th Cir. 1981); Farmers Cooperative Grain and Supply Company, 10 BNA OSHRC 2086 (No. 79-1177, 1982).

  • Citations for violations of 1910.22(a)(1) shall be issued when the levels of dust accumulations (see sections II.E.3.c and d of this Instruction) exist in places of employment (except floors of workrooms and storage areas), passageways, and service rooms in such depths that then can present explosion, deflagration or other fire hazards.
  • Citations for 1910.22(a)(2) shall be issued when the levels of dust accumulations (see sections II.E.3.c and d of this Instruction) exist on the floors of workrooms in such depths that they can present explosion, deflagration or other fire hazards.

However, small amounts of dust accumulations in isolated spots of the floor or other areas would not normally be classified as a violation of the housekeeping requirement under this NEP. In order to substantiate housekeeping violations, CSHOs shall take representative measurements. Thickness measurements must be made at several locations within the sampling area. As a part of determining whether the housekeeping violation is serious, the CSHO should determine whether the dust is combustible or can cause deflagration by submitting the sample to SLTC and obtaining its analyses. [For a large area, a paint brush and dustpan can be used to collect the sample. For a small area, a high-volume pump pulling through a filtered cassette may be used to collect the sample.] In addition the CSHO should also document the heat and ignition sources.

In coal-handling operations located in electric power generation, transmission, and distribution facilities, 29 CFR 1910.22 shall not be cited for coal dust accumulations; rather 29 CFR 1910.269(v)(11)(vii) shall be cited. See subparagraph IX.E.9.f.

NOTE: This NEP should not be construed to interfere with the application of 1910.22 or other housekeeping standards to the uncleanliness of workplaces unrelated to the combustible dust hazard.

d. Housekeeping violations in storage areas. 1910.176(c) shall be cited for housekeeping violations in storage areas. The standard provides in pertinent part: "(c) Housekeeping. Storage areas shall be kept free from accumulation of materials that constitute hazards from …fire, explosion…" The criteria for the dust hazard applicable to 1910.22(a) violations under this NEP apply in determining 1910.176(c) violations. The CSHO must document whether a reasonable person would recognize a combustible dust hazard under the circumstances. NFPA standards may be relied upon in this regard. See, e.g., NFPA 654 (2006), Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. The CSHO must also document feasible abatement methods. See, e.g., NFPA 654.

e. Labor and Employment Article 5-104(a): general duty clause violations. A citation under Labor and Employment Article 5-104(a) may be issued for deflagration, explosion or other fire hazards that may be caused from combustible dust within a dust collection system or other containers, such as mixers. The NFPA standards, which represent the opinions of experts familiar with combustible dust hazards, are useful in providing evidence of industry recognition of the hazard. See, e.g., NFPA 654 (2006), Standard for the Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids. (See Kelly Springfield Tire Co., Inc. v. Donovan, 729 F.21 317 (5th Cir. 1984) (recognition of combustible dust hazard based on testimony of expert employed by dust collection equipment manufacturer.) CSHOs should also search for articles dealing with the combustible dust hazard in publications dealing with the employer's industry. CSHOs shall also look at the employer's safety manuals or other instructions to determine whether there is employer recognition of the combustible dust hazard. However, if such articles or employer documents are unavailable, CSHOs may rely upon the NFPA standards for evidence of recognition of the hazard. For evidence of feasible means of abatement, CSHOs should consult relevant NFPA standards. The essence of a L&E 5-104(a) citation is the hazard. A separate L&E 5-104(a) citation shall not be issued for a failure to use a particular abatement method. The Assistant Attorney General's Office should be consulted prior to issuing L&E Article 5-104(a) citations.

  • However, when inspecting bakery equipment in a bakery covered under 1910.263, general duty clause citations shall not be issued for fire and explosion hazards in connection with sugar and spice pulverizers, covered under 1910.263(k)(2).
  • Additionally, general duty clause citations shall not be issued with respect to explosion hazards from blower collection and exhaust systems in sawmill operations covered under 1910.265(c)(20)(i).

L&E Article 5-104(a) citations may be issued for deflagration and explosion hazards if SLTC finds Kst values of the submitted dust sample to be greater than zero. L&E 5-104(a) citations may also be issued for other fire hazards if SLTC determines that the dust is combustible. (See Appendix F.5 for more details on combustible dust tests, including the Kst test and its associated values relative to degree of explosion). General duty clause citations can only be issued if all elements of a L&E 5-104(a) violation can be documented. As a part of L&E 5-104(a) documentation, the CSHO should also document the heat and ignition sources.

The following are some conditions for which a general duty clause citation (See Appendix D for sample citations) may be issued:

  • Problems related to dust collectors, e.g., dust collection equipment located inside the building (however, there are some exceptions) and dust collectors returning air back inside the building.
  • Ductwork-related problems, e.g., the ductwork not being grounded and ductwork not constructed of metal.
  • Improperly designed deflagration venting (venting to areas where employees are likely to be exposed to explosion/deflagration hazards).
  • Processing and material handling equipment, such as, mixers, blenders, pulverizers, mills, dryers, ovens, filters, dust collectors, pneumatic conveyors, and screw conveyors, not protected by deflagration suppression systems.
  • Equipment connected by pipes and ducts not protected by deflagration isolation systems, such as flame arresters, flame front diverters, spark detection, spark extinguishing equipment, and rotary valves.

(Note: If all the elements of a L&E Article 5-104(a) violation cannot be documented for the hazards noted during an inspection, then a Hazard Alert letter shall be issued to the employer for such hazards. The letter is to be sent from the regional office signed by the Supervisor after consultation with the Chief.)

f. Housekeeping violations at coal-handling operations covered under 1910.269. If violations of 1910.269(v)(11)(xii) (sources of ignition not eliminated or controlled where coal-handling operations may produce a combustible atmosphere from fuel sources) are identified during an inspection of a coal-fired power plant, that provision shall be cited, not 1910.22 or section L&E 5-104(a).

g. Personal Protective Equipment (PPE) Violations. Citations under 1910.132(a) (the general requirement to provide and assure the use of protective equipment, including protective clothing) may be issued, if an employee exposure to potential burn injuries can be documented. For example, if employees are not wearing protective clothing, such as flame-resistant clothing, in areas of the plant (e.g., bagging areas) where employees may be exposed to potential flash fire hazards, then citations under 1910.132(a) may be issued. Another example where citations under 1910.132(a) may be issued would be a situation where employees (not wearing flame resistant clothing) cleaning out a piece of equipment containing combustible dust may be exposed to a flash fire propagated through the cleanout door. A citation may be issued whether or not an accident precipitated the inspection.

The CSHO shall document whether a reasonable person familiar with the circumstances would recognize hazards from combustible dust. NFPA standards may be used for this documentation. The CSHO shall also document whether there are feasible types of personal protective equipment to deal with these hazards. It has been recognized as industry practice to require flame-resistant clothing when employees may be exposed to flash fire hazards. National Fire Protection Association (NFPA) 2113, Standard on Selection, Care, Use and Maintenance of Flame-Resistant Garments for Protection of Industrial Personnel Against Flash Fire is a national consensus standard which applies to, among others, chemical, refining, and terminal facilities with flash fire hazards. Among other provisions, NFPA 2113 has requirements for when flame-resistant clothing must be used by industrial personnel exposed to flash fire hazards. See Chapter 4 of NFPA 1123 for a discussion on selection of flame-resistant clothing.

h. Process Safety Management. If the dust in question appears on the list of Highly Hazardous Chemicals (Appendix A to 29 CFR 1910.119) and is present in quantities greater than or equal to the listed threshold quantity, the PSM standard will apply. Citations under 1910.119 shall be issued for PSM violations.

i. Electrical Violations. If the laboratory analysis indicates that the submitted dust meets the criteria for Class II (See Class II Test methodology in Appendix F), and if the location where the dust was present falls under any of the Class II location definitions, then 29 CFR 1910.307 will apply. See the Class II definition in 29 CFR 1910.399. However, if violations involving Class I or III locations are found in the course of conducting an inspection under this NEP, citations shall be issued. See the Class I and III definitions in 29 CFR 1910.399.

Equipment, wiring methods, and installations of equipment in hazardous (classified) locations shall be: 1) intrinsically safe, 2) approved for the hazardous (classified) location, or 3) safe for the
hazardous (classified) location. The meaning of these terms is spelled out in 29 CFR 1910.307(c) If the employer chooses the third option of providing equipment that is "safe for the hazardous location," then the employer must demonstrate that the equipment is of a type and design that will provide protection from the hazards involved. Compliance with the guidelines contained in the National Electrical Code (NEC) constitutes one means, but not the only means, of demonstrating that the electrical equipment is safe for the hazardous location.

Citations issued for electrical violations must be adequately documented in the case file. Such documentation must include the location and type of potential electrical ignition sources, the type and condition of electrical equipment located in the area, and information indicating that the equipment is not approved or safe for the location. (See NEC and NFPA 499 for more details.)

j. Powered Industrial Trucks. For powered industrial truck violations, citations shall be issued under 1910.178(c)(2)(ii) and (vi)-(ix) and 1910.178(m)(11).

k. Welding, cutting, and brazing. For violations involving welding, cutting, and brazing operations, 1910.252 (general welding and cutting) (see, in particular, (a)(2)(vi)(C), prohibiting cutting and welding in explosive atmospheres, including mixtures of flammable dusts with air), 1910.253 (oxygen-fuel gas welding and cutting) (see, in particular, (c)(2)(ii) and (iv), and (f)(5)(i)(B)), and 1910.254 (arc welding) (see, in particular, (b)(2)(F)) shall be used.

l. Warning Sign Violations. If safety instruction signs are missing on equipment, or at the entrance to places where explosive atmospheres may occur, then citations under 29 CFR 1910.145(c)(3) shall be issued.

m. Hazard communication violations. The hazard communication standard, 29 CFR 1910.1200, requires all employers to provide information to their employees about the hazardous chemicals to which they are exposed, by means of a hazard communication program, labels and other forms of warning, material safety data sheets, and information and training. See "hazardous chemicals" definition in 29 CFR 1910.1200(c), which addresses physical hazards. The definition of physical hazards includes flammable solids (see the definition in .1200(c)), and employers who do not follow the requirements of this standard shall be cited with respect to chemicals which in the course of normal conditions of use could become combustible dusts. The standard requires chemical manufactures and importers to develop or obtain a material safety data sheet for each hazardous chemical they produce or import [29 CFR.1200(g)(1)].

CSHO's shall evaluate where there is compliance with 29 CFR 1910.1200(g)(2)-(5) by examining a sample of MSDSs. If MSDSs are not updated when new information becomes available, they are deficient [29 CFR 1910.1200(g)(5)]. If the MSDSs are found deficient with respect to the combustibility or explosibility of the dust being handled, CSHOs must refer to and follow the guidance provided in CPL 02-02-038, Inspection Procedures for the Hazardous Communication Standard.

n. Egress violations. Citations for violations of Subpart E -Means of Egress, Part 1910, particularly 29 CFR 1910.33-37, shall be issued where violations of these provisions are found.

o. Fire protection violations. Citations for violations of 29 CFR 1910.156 (fire brigades) and 1910.157 (portable fire extinguishers) shall be issued where violations of these standards are found. 1910.156 only applies in the context of this NEP if the employer has a fire brigade or industrial fire department. The fire extinguisher provisions of 1910.157 do not apply where the employer requires the evacuation of employees in the event of fire, has an emergency action plan meeting the requirements of 1910.38, and has a fire prevention plan meeting the requirements of 1910.39.

p. Bakery equipment violations. Citations for violations of 29 CFR 1910.263(k)(2) shall be issued for fire and explosion hazards in sugar and spice pulverizers.

q. Sawmill violations. Citations for violations of 29 CFR 1910.265(c)(20)(i) shall be issued in connection with defects in the design, construction, and maintenance of blower collecting and exhaust systems.

r. Agriculture. The only provisions discussed in this NEP which may be cited in connection with agricultural operations are the hazard communication standard (see 29 CFR 1928.21) and the general duty clause. Industries in SIC 0723, Crop Preparation Services for Market, Except Cotton Ginning, listed in Appendix E, are engaged in agricultural operations.

Because 29 CFR 1910.22(a) and 29 CFR 1910.176(c) do not apply to agricultural operations, the general duty clause may apply to hazards associated with surface dust accumulations outside and within dust collection systems and other containers.

F. Program Evaluation.

IMIS case files coded "DUSTEXPL" can be retrieved for program evaluation purposes by the Assistant Commissioner based on agency evaluation priorities. Case files will be requested from the Regional Offices by the Chief of Compliance as needed.

G. Outreach

MOSH Outreach will monitor the federal development of related materials for use within our jurisdiction.

H. IMIS Coding Instructions.

1. All enforcement activities (inspections, complaints, accidents and referrals) and compliance assistance (OSHA 55) conducted under this NEP must be coded with the NEP code "DUSTEXPL" entered in the appropriate NEP field/item number on the respective forms.

2. Enforcement activities related to dust hazards under other NEPs and/or LEPs must be coded for all the NEPs and LEPs. For example, combustible dust inspections conducted under Amputations NEP should be coded "AMPUTATE", as well as "DUSTEXPL.

3. All consultation activities (form 20, 30 and 66) conducted in response to this NEP must include "DUSTEXPL" in the National Emphasis Field on the forms as well.

III. Appendices: The following appendices are provided as guidance for the inspection of facilities handling combustible dust.

Appendix A: NFPA Publications Relevant to Combustible Dust Hazard Controls.

Appendix B: Sample Questions.

Appendix C: Sample Citations.

Appendix D: Industries that May have Combustible Dusts.

Appendix E: Combustible Dusts Test Conducted at SLTC.

Appendix F: References.

Return to top of page