Explosives and blasting definitions

A blasting agent is any fuel-and-oxidizer mixture intended for blasting whose ingredients are not classified as explosives and that cannot be detonated by a No. 8 test blasting cap when unconfined. This means the product is designed for blasting but will not detonate from a standard test cap when unconfined. See the definition at 1910.109(a)(1).

Practical tips:

• If an ingredient in the mixture is itself classified as an explosive, the finished product is not a blasting agent under this definition.
• Manufacturers or testing labs can confirm whether a No. 8 test blasting cap will detonate the finished product; a negative result supports classification as a blasting agent.
• For regulatory classification questions, rely on the manufacturer’s specifications and DOT classification guidance referenced in the explosives definitions.

An explosive is any chemical compound, mixture, or device whose primary purpose is to function by explosion — a substantially instantaneous release of gas and heat — and includes materials classified by DOT as Class A, B, or C. Common examples listed include dynamite, black powder, blasting caps, safety fuse, small arms ammunition, and smokeless propellant. See the definition at 1910.109(a)(3) and the related Class A/B/C descriptions at 1910.109(a)(3)(i) and 1910.109(a)(3)(ii).

Practical notes:

• If DOT already classifies a material (49 CFR), follow that DOT classification when applying OSHA definitions.
• “Commercial explosives” refers to explosives intended for industrial or commercial use.

Class A explosives are those that pose a maximum hazard (e.g., dynamite, lead azide, blasting caps), Class B explosives possess a flammable hazard such as some propellant explosives and photographic flash powders, and Class C explosives are manufactured articles that contain Class A or B components in restricted quantities. See the classifications at 1910.109(a)(3)(i), 1910.109(a)(3)(ii), and 1910.109(a)(3)(iii).

Key takeaways:

• Class A: highest detonation/detonability hazards — treat and store with the strictest controls.
• Class B: primarily flammable hazards (some propellants).
• Class C: articles that contain limited quantities of Class A/B explosive components and are treated differently for storage/transport considerations.

A magazine is any building or structure, other than an explosives manufacturing building, used for the storage of explosives. See the definition at 1910.109(a)(6).

Practical points:

• Magazines are specifically for storage, not manufacturing.
• Different magazine classes (Class I and II) are specified elsewhere in 1910.109(c) and determine construction and location requirements.

No; blasting caps, electric blasting caps, detonating primers, and primed cartridges must not be stored in the same magazine with other explosives. See the prohibition at 1910.109(c)(1)(ii).

Why this matters:

• Caps and primed devices are highly sensitive and present a much greater initiation risk, so OSHA requires separate storage to reduce accidental detonation risks.

You must keep the ground around magazines sloped for drainage and the surrounding land clear of brush, dried grass, leaves, and other materials for at least 25 feet. This requirement is stated at 1910.109(c)(1)(iii).

Practical steps:

• Grade the ground so water runs away from the magazine.
• Maintain a 25-foot clear zone free of combustible vegetation and debris to reduce fire and spread risks.

A Class I magazine is required where the quantity of explosives stored is more than 50 pounds; a Class II magazine may be used where the quantity stored is 50 pounds or less. See 1910.109(c)(1)(v).

Practical notes:

• Plan storage based on net weight of explosives to choose the correct magazine class.
• Class I magazines have stricter location and construction requirements (see 1910.109(c)(1)(vi)).

Separation distances for Class I magazines must follow the American Table of Distances shown as Table H‑21; the table specifies feet of required separation based on the pounds of explosives stored. See 1910.109(c)(1)(vi) and the Table H‑21 contained there.

Practical guidance:

• Identify the total pounds stored in a magazine, find the corresponding row in Table H‑21, and apply the listed separation distances to other magazines, inhabited buildings, railways, and highways.
• If magazines are closer together than the table’s “Separation of Magazines” distance, treat them as one magazine and use the combined quantity to determine required distances (see the note in Table H‑21 and 1910.109(c)(1)(vii)).

Yes, Class II magazines may be located in warehouses and in wholesale and retail establishments when placed on a floor with an entrance at outside grade level and the magazine is not more than 10 feet from that entrance; two Class II magazines may be in the same building if one is used only for blasting caps (≤5,000 caps) and a 10-foot distance is kept between them. For temporary storage at a blasting site, Class II magazines must be located away from other magazines. See 1910.109(c)(1)(vii) and 1910.109(c)(1)(viii).

Practical reminders:

• When storing in a warehouse, ensure the floor and outside-grade entrance condition are met.
• For on-site temporary storage, keep the magazine isolated from permanent magazines.

Paragraph (c) does not apply to: (a) stocks of small arms ammunition, propellant-actuated power cartridges, small arms ammunition primers in quantities less than 750,000, or smokeless propellants less than 750 pounds; (b) explosive-actuated power devices when under 50 pounds net weight of explosives; (c) fuse lighters and fuse igniters; and (d) safety fuses other than cordeau detonant fuses. See the list at 1910.109(c)(1)(ix).

Practical application:

• If your stock fits any of these categories and stays below the limits listed, the magazine construction/location rules in paragraph (c) do not apply.
• Keep documentation to show quantities and that an exemption applies in case of inspection.

If a Class II magazine holds more than 25 pounds of explosives, maintain at least 150 feet between the magazine and the work in progress; if it holds 25 pounds or less, maintain at least 50 feet. This requirement is in 1910.109(c)(1).

Practical points:

• Measure the net explosive quantity in the magazine before determining the required distance to active blasting or work areas.
• For temporary site magazines, also follow the separate temporary-location guidance in 1910.109(c)(1)(viii).

You must post the property upon which Class I magazines are located and property where Class II magazines are located outside of buildings with signs reading “Explosives - Keep Off.” See the signage requirement at 1910.109(c)(2)(iii).

Practical tips:

• Place signs where they are clearly visible to prevent unauthorized access.
• Keep signs maintained so they remain legible and present.

Magazines for storing explosives other than black powder, Class B, and Class C explosives must be bullet resistant, weather resistant, fire resistant, and ventilated sufficiently to protect the explosives for the specific locality. Magazines storing black powder, Class B and Class C explosives must be weather resistant, fire-resistant, and have ventilation; magazines for blasting and electric blasting caps must be weather resistant, fire-resistant, and ventilated. See 1910.109(c)(2)(ii).

Practical guidance:

• Use construction materials and ventilation appropriate to local conditions (humidity, temperature, precipitation).
• For higher hazard explosives, ensure bullet-resistant construction and documented design that meets the listed criteria.

Magazine heating systems must use hot-water radiant heating or air directed over hot water or low-pressure steam coils located outside the magazine; heating installations must prevent explosives or containers contacting radiant coils, must not direct hot-air discharge against explosives/containers, must have controls preventing magazine ambient temperature from exceeding 130 °F, and magazine heating fans or pumps must be mounted outside and grounded. These requirements are found at 1910.109(c)(2)(iv) and 1910.109(c)(2)(v), including subparts (a)–(d) at the same location.

Practical checklist:

• Keep heating coils separated from explosives so nothing can contact the coils and airflow can circulate.
• Orient ducts so hot air does not blow directly onto explosives or containers.
• Install temperature controls that cap ambient temperature at 130 °F.
• Mount and ground fans/pumps outside the magazine wall.

OSHA prohibits storing, handling, or transporting explosives or blasting agents when those activities create an undue hazard to life — meaning conditions that pose an unreasonable risk of injury or death to employees or the public. This general prohibition is stated at 1910.109(b)(1).

How to apply this practically:

• Evaluate whether storage location, quantities, construction, separation distances (see Table H‑21), signage, and handling procedures create unacceptable risk.
• Mitigate undue hazards by reducing quantities, moving magazines, improving construction/ventilation, increasing separation, or using administrative controls and training.
• Document hazard assessments and corrective actions to demonstrate due diligence in reducing risks.

Yes — storing pre-charged air conditioners or heat pumps in one location where the aggregate weight of a Category 1 flammable gas meets or exceeds 10,000 pounds triggers coverage under OSHA’s Process Safety Management standard for a covered process. The Letter of Interpretation explains that storage and on-site movement of pre-charged units constitute a "process" under the PSM rule when the threshold quantity is met. See the June 6, 2024 Letter of Interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06 and the general PSM application discussion in that letter. Also see OSHA’s general rule collection at 1910 for context.

Practical actions employers should take:

• Inventory and aggregate the total refrigerant weight on-site to determine if the 10,000 lb threshold is reached.
• If covered by PSM, implement required PSM elements (process safety information, hazard analysis, operating procedures, training, emergency response, etc.) as described in PSM guidance.
• Consult the referenced Letter of Interpretation for rationale and examples to help determine coverage.

If crane operators are exposed to potential head injury from falling objects (for example from an overhead load), employers must ensure operators wear protective helmets that meet OSHA’s head protection requirements. The June 6, 2024 Letter of Interpretation states that 29 CFR 1910.135(a)(1) applies when there is a potential for head injury while operating cranes. See the Letter of Interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-06-06-2 for details.

Practical steps:

• Perform a hazard assessment under 29 CFR 1910.132(d)(1) to determine if head hazards exist.
• Provide helmets that comply with ANSI Z89.1 consensus standards as required by 29 CFR 1910.135(b)(1).
• Require and enforce helmet use wherever overhead hazards are present.

When temporary re-energization for testing or positioning is necessary, the employer must follow the sequence in 1910.147(f)(1): clear tools/materials, remove employees from hazardous areas, remove the lockout/tagout devices as specified, energize the machine while using effective employee protection during testing/positioning, then de-energize and reapply energy control measures if further servicing is needed. This procedure and sequence are explained in the October 21, 2024 Letter of Interpretation at https://www.osha.gov/laws-regs/standardinterpretations/2024-10-21 and reference 1910.147 requirements noted in that letter.

Practical reminders:

• Limit the energized period strictly to the time needed for testing or positioning.
• Use guarding or barriers to protect employees if they must be near energized equipment during testing.
• Document the steps and the authorized employees performing them to maintain compliance.

The heating device used in connection with a magazine must have controls that prevent the ambient building temperature from exceeding 130 °F. See 1910.109(c)(2)(v)(c).

Practical notes:

• Install reliable temperature controls and alarms to prevent overheating.
• Verify and log temperatures periodically, especially in cold climates where heating runs continuously.

A semiconductive hose is defined as a hose with electrical resistance low enough to drain static to ground but high enough to limit stray current: not more than 2 megohms resistance over its entire length and not less than 5,000 ohms per foot meets the requirement. See the semiconductive hose definition at 1910.109(a)(12).

Practical guidance:

• Use hoses that meet the specified resistance range when transferring fuels or explosive-sensitive materials to control static charge.
• Periodically test hoses for resistance to ensure ongoing compliance and safety.

Electrical switch gear must be located at least 25 feet from the magazine, and electric fan motors and controls for electrical heating devices used for heating water or steam must have overloads and disconnects that comply with subpart S.

• See the requirement in 1910.109(c)(2)(v)(e).
• For the referenced electrical equipment requirements, consult 1910 (subpart S) for applicable overload and disconnect rules.

The heating source for water or steam must be separated from the magazine by at least 25 feet when electrically powered and at least 50 feet when fuel fired; the area between the heating unit and the magazine must be cleared of all combustible materials.

• See the separation and clearance requirements in 1910.109(c)(2)(v)(f).

Explosives and their containers must be stored to allow uniform air circulation so product temperature uniformity can be maintained.

• See the storage ventilation requirement in 1910.109(c)(2)(v)(g).

When lights are necessary inside the magazine, only electric safety flashlights or electric safety lanterns shall be used.

• See the lighting requirement in 1910.109(c)(2)(vi).

Class I magazines may be masonry, wood, metal, or combinations, and masonry units must be at least 8 inches thick; hollow masonry units required to be bullet resistant must have hollow spaces filled with weak cement or well-tamped sand.

• See the Class I construction rules in 1910.109(c)(3)(i).

Magazine floors and roofs may be of wood construction; wood floors must be tongue-and-groove lumber with a nominal thickness of 1 inch.

• See the flooring and roofing allowance and wood floor specification in 1910.109(c)(3)(ii).

Roofs required to be bullet resistant must be protected by a sand tray at the line of eaves covering the entire area except ventilation openings, with sand maintained at a depth of not less than 4 inches.

• See the sand-tray requirement in 1910.109(c)(3)(iii).

All exterior wood of magazines, including eaves, must be covered with black or galvanized steel or aluminum metal of at least No. 26 gauge; all nails exposed to the interior must be well countersunk.

• See the exterior covering and nail requirements in 1910.109(c)(3)(iv).

Foundations must be of substantial construction and arranged to provide good cross ventilation; magazines must be ventilated sufficiently to prevent dampness and heating of stored explosives, and ventilating openings must be screened to prevent entrance of sparks.

• See the foundation requirement in 1910.109(c)(3)(v) and the ventilation rule in 1910.109(c)(3)(vi).

Openings to magazines must be limited to what is needed for placing and removing explosives; doors for Class A magazines must be bullet resistant, and doors for non-bullet-resistant magazines must prevent unauthorized entry. Stocks of explosives must not be piled directly against masonry walls, brick-lined or sand-filled metal walls, or single-thickness metal walls, though whatever protection is used must not interfere with interior ventilation.

• See opening and door design rules in 1910.109(c)(3)(vii) and the piling/clearance rule in 1910.109(c)(3)(ix).

Class II magazines may be wood or metal; wood magazines must have 2-inch hardwood sides, bottom, and cover, be well braced and fully covered with sheet metal not less than No. 20 gauge, and metal magazines must be lined with 3/8-inch plywood or equivalent with metal cover edges overlapping at least 1 inch. Covers must have substantial strap hinges and locking means; magazines must be painted red and bear white lettering at least 3 inches high saying "Explosives - Keep Fire Away."

• See the Class II construction and marking requirements in 1910.109(c)(4)(i)–(iv).

Packages of explosives must be laid flat with the top side up, corresponding grades and brands stored together with marks visible, piled stably, and when removed for use the oldest explosive of that kind must be taken first (first-in, first-out). Black powder stored with other explosives must be stored separately, and kegs of black powder have special positioning rules.

• See the storage and rotation rules in 1910.109(c)(5)(i).

Explosives packages shall not be unpacked or repacked inside a magazine, within 50 feet of a magazine, or in close proximity to other explosives.

• See the unpacking/repacking prohibition in 1910.109(c)(5)(ii).

Tools used inside magazines for opening packages must be made of nonsparking materials (metal slitters allowed for fiberboard); brooms and cleaning utensils must not have spark-producing metal parts; magazine floors must be kept clean, dry, and free of grit, paper, empty packages, and rubbish, and sweepings must be disposed of properly.

• See the tool and cleaning rules in 1910.109(c)(5)(iii) and 1910.109(c)(5)(iv).

If an explosive has deteriorated to an unstable or dangerous condition or nitroglycerin leaks from explosives, the person in possession must immediately destroy the explosive following the manufacturer's instructions, and only experienced persons should perform the destruction.

• See the requirement to destroy deteriorated explosives in 1910.109(c)(5)(v).

When inside repairs are needed, all explosives must be removed and the floors cleaned; for outside repairs that might cause sparks or fire, explosives must be removed and either placed in another magazine or at a safe guarded distance until repairs are complete.

• See the repair and removal rules in 1910.109(c)(5)(vi).

Smoking, matches, open flames, spark-producing devices, and firearms (except those carried by guards) are prohibited inside or within 50 feet of magazines; the land surrounding a magazine must be cleared of combustible materials for at least 25 feet, and combustibles shall not be stored within 50 feet.

• See the prohibitions and clearing distances in 1910.109(c)(5)(vii).

A competent person must be in charge of the magazine at all times and is responsible for enforcing all safety precautions related to magazine operations.

• See the requirement for a competent person in 1910.109(c)(5)(viii).

Explosives recovered from blasting misfires must be placed in a separate magazine until competent personnel consult the manufacturer on disposal; caps recovered from misfires must not be reused and should be disposed of per the manufacturer's recommendations.

• See the misfire recovery rules in 1910.109(c)(5)(ix).

Employees in or near motor vehicles transporting explosives may not smoke, carry matches or other flame-producing devices, or carry firearms or loaded cartridges; explosives shall not be transferred between vehicles within a jurisdiction without informing the fire and police departments, and blasting caps may not be transported on the same vehicle with other explosives unless packaged, segregated, and transported under DOT Hazardous Materials Regulations (49 CFR parts 177–180).

• See the general transportation provisions in 1910.109(d)(1)(i), 1910.109(d)(1)(iii), and 1910.109(d)(1)(iv).

Vehicles must be strong enough for the load and in good mechanical condition; if the vehicle body is open, it must be covered with a flameproof and moistureproof tarpaulin or equivalent, have tight floors, and any exposed spark-producing metal inside must be covered with wood or other nonsparking materials; packages must not be loaded above the sides of an open-body vehicle.

• See vehicle condition and loading requirements in 1910.109(d)(2)(i) and the open-body protection rule in 1910.109(d)(2) (see paragraph on open body).

Vehicles carrying explosives must display markings or placards: "Explosives A" for Class A (red letters on white background) and "Explosives B" for Class B (red on white); oxidizing materials of 1,000 pounds or more must be marked "Oxidizers" (yellow letters on black background). Placards must be displayed at the front, rear, and each side while the vehicle contains specified quantities, and when a vehicle contains more than one kind of explosive plus an oxidizer totaling 1,000 pounds or more the vehicle must be marked "Dangerous" as well as the appropriate explosive marking.

• See the marking and placarding rules in 1910.109(d)(2)(ii)(a), display locations in 1910.109(d)(2)(ii)(c), and combined-load marking in 1910.109(d)(2)(ii)(d) and 1910.109(d)(2)(ii)(e).

Each motor vehicle used to transport explosives must be equipped with a minimum of two extinguishers, each rated at least 10-BC, and extinguishers must be listed or approved by a nationally recognized testing laboratory as defined in 1910.155(c)(3)(iv)(A) and the laboratories are defined in 1910.7. Extinguishers must be filled, ready for immediate use, located near the driver's seat, and examined periodically by a competent person.

• See the vehicle extinguisher requirement in 1910.109(d)(2)(iii), suitability and listing in 1910.109(d)(2)(iii)(a) and definitions in 1910.155(c) and 1910.7.

Before transporting explosives, the vehicle must be inspected to ensure fire extinguishers are filled and working; all electrical wiring is protected and securely fastened; chassis, motor, pan, and underside are clean and free of excess oil/grease; fuel tank and feedline are secure with no leaks; brakes, lights, horn, windshield wipers, and steering function properly; tires are checked for inflation and defects; and the vehicle is otherwise in proper condition for handling explosives.

• See the required inspection items in 1910.109(d)(2)(iv) and its subparagraphs (a)–(g) for details.

A vehicle transporting Class A or Class B explosives is considered "attended" only when the driver or attendant is physically on or in the vehicle, or has the vehicle within his field of vision and can reach it quickly, and is awake, alert, and not engaged in other duties that would divert attention (with narrowly defined exceptions). See 1910.109(d)(3)(iii)(a).

• Exceptions where limited absence is allowed include necessary communication with public officers or carrier/shipper/consignee representatives, and short absences to obtain food or provide for physical comfort.
• If you must leave an explosives-laden vehicle unattended, it may only be left in a securely fenced or walled area with all gates locked or at an authorized magazine site; see 1910.109(d)(3)(iii)(b).
• Practical steps: ensure drivers/attendants are trained about the cargo and dangers, stay alert while attending the vehicle, and avoid activities that divert attention from the vehicle.

Except under emergency conditions, a vehicle transporting explosives may not be parked on a public street adjacent to or in proximity to a place where people work before reaching its destination, even if it is attended. See 1910.109(d)(3)(ii).

• Plan routes and delivery schedules so stopping in public streets near workplaces is avoided.
• If stopping is unavoidable due to an emergency, document the reason and follow any local authority requirements; otherwise use authorized magazines, locked fenced areas, or designated safe parking per 1910.109(d)(3)(iii)(b).
• Employers should train drivers on parking restrictions and emergency procedures to reduce public risk.

You must not carry spark-producing metal, spark-producing metal tools, oils, matches, firearms, electric storage batteries, flammable substances, acids, oxidizing materials, or corrosive compounds in the body of a vehicle transporting explosives unless loading those items with the explosives complies with U.S. Department of Transportation regulations. See 1910.109(d)(3)(iv).

• If you believe an item is necessary to carry (for example, as required by DOT packaging or transport rules), verify compliance with the applicable 49CFR requirements before loading.
• Best practices: remove or segregate prohibited items from the cargo compartment, use approved containers/magazines for detonators and explosives, and document DOT approvals when exceptions apply.

The blaster must notify the appropriate representatives of gas, electric, water, fire alarm, telephone, telegraph, and steam utilities at least 24 hours in advance of blasting, specifying the location and intended time; verbal notice must be confirmed in writing. See 1910.109(e)(1)(vi).

• Provide the exact blast location, planned start time, and any staging or access information so utility representatives can take precautions.
• Keep copies of the written confirmations and records of notifications as part of your blasting pre-job documentation.
• When blasting close to utilities, also follow other precautions in 1910.109(e)(1) such as warning signals and public protection measures.

When loading blasting agents pneumatically over electric blasting caps, you must use semiconductive delivery hose and ensure the equipment is bonded and grounded. See 1910.109(e)(3)(iii).

• Semiconductive hose prevents static buildup in the delivery line; bonding and grounding equalize electrical potential between equipment to prevent stray currents or sparks.
• Practical steps: inspect hose conductivity before use, attach bonding clamps per manufacturer guidance, connect ground to a verified earth ground, and document inspections and maintenance of bonding/grounding systems.

If a misfire occurs when using cap and fuse, all persons must remain away from the charge for at least 1 hour; if electric blasting caps are used, the waiting period may be reduced to 30 minutes. After a misfire, misfires must be handled under the direction of the person in charge, all wires should be traced carefully, and a search made for unexploded charges. See 1910.109(e)(4)(vi) and 1910.109(e)(4)(vii).

• Only authorized personnel should approach or attempt to deal with misfires, and they should follow an established misfire procedure directed by the person in charge.
• When testing charged holes, use only blasting galvanometers designed for the purpose (see 1910.109(e)(4)(vii)).
• After dealing with a misfire, return all excess caps and explosives immediately to their separate storage magazines as required by 1910.109(e)(3)(vii).