Temporary heating device safety

Fresh air must be supplied in sufficient quantities to maintain the health and safety of workers, and mechanical ventilation must be provided where natural fresh-air supply is inadequate. See the ventilation requirement in 1926.154(a)(1).

• "Sufficient quantities" means providing enough outside air (or equivalent mechanical ventilation) so combustion is complete and workers are not exposed to harmful gases, oxygen depletion, or unsafe heat levels.
• If natural ventilation isn’t adequate, install mechanical ventilation and document the method used to show compliance.

You must provide special care to ensure enough ventilation for proper combustion, to protect workers’ health and to limit temperature rise when heaters are used in confined spaces. See 1926.154(a)(2).

• Provide continuous make-up air so the heater has adequate oxygen for complete combustion.
• Vent combustion products (CO, CO2, NOx) to the outside or use rated exhaust systems; monitor air with CO and oxygen sensors when workers occupy the space.
• Limit temperature rise with ventilation or by selecting lower-heat output units.
• Ensure personnel trained in confined-space hazards perform and document hazard assessments (see OSHA PPE hazard-assessment guidance: LOI 2024-03-28).

Minimum clearances depend on heater type: for a circulating room heater the minimum clearances are 12 inches to the sides, 12 inches to the rear, and 18 inches to the chimney connector; for a radiant room heater the minimum clearances are 36 inches to the sides, 36 inches to the rear, and 18 inches to the chimney connector. See 1926.154(b)(1) and Table F-4 in that section.

• Keep clearances at or beyond the table values unless the appliance is specifically listed for smaller clearances (see 1926.154(b)(2)).
• Measure clearances from the hottest part of the heater to combustible material.

Yes — a temporary heating device that is listed (approved) for installation with lesser clearances may be installed according to its listing or approval instead of the Table F-4 distances. See 1926.154(b)(2).

• Keep and follow the manufacturer’s installation instructions and the listing documentation that authorizes the reduced clearances.
• Maintain documentation (listing/certification) on site to show why you used smaller clearances.

No — heaters not suitable for use on wood floors must not be set directly on wood or other combustible materials; they must rest on suitable heat-insulating material or at least 1-inch concrete (or equivalent). See 1926.154(b)(3).

• The insulating material must extend at least 2 feet beyond the heater in all directions.
• "Suitable heat insulating material" means a material that prevents heat transfer and ignition — retain supplier/manufacturer specs to document suitability.

Heaters must be located at least 10 feet from combustible tarpaulins, canvas, or similar coverings, and those coverings must be securely fastened to prevent ignition or the heater being upset by wind. See 1926.154(b)(4).

• Fasten coverings so wind cannot blow them onto the heater or tip the heater over.
• If work conditions make a 10-foot separation impossible, stop and re-evaluate heater placement or use a different heating method that reduces ignition/upset risk.

Heaters must be set horizontally level when in use unless the manufacturer's markings or instructions permit otherwise. See 1926.154(c).

• Follow the manufacturer’s orientation instructions exactly; if the unit is tipped or not level it may not operate safely.
• Use level surfaces or secure mounts to prevent accidental tipping.

No — solid fuel salamanders are prohibited in buildings and on scaffolds. See 1926.154(d).

• Do not use wood-, coal-, or other solid-fuel salamanders in these locations; select compliant heating options (oil-fired, gas, or electric heaters that meet installation requirements).

Flammable liquid–fired heaters must have a primary safety control that stops fuel flow in the event of flame failure; barometric or gravity oil feed does not count as a primary safety control. See 1926.154(e)(1).

• Acceptable primary safety controls include automatic shutoff valves or other approved devices that actively stop fuel delivery when the flame goes out.
• Do not rely on passive gravity or barometric feed as the sole safety measure.

Heaters designed for barometric or gravity oil feed may be used only with their integral tanks. See 1926.154(e)(2).

• Do not connect those heaters to remote or separate supply tanks unless the heater is specifically designed and approved for that arrangement (see 1926.154(e)(4)).

Only heaters that are specifically designed and approved for use with separate supply tanks may be directly connected for gravity feed or by an automatic pump from a supply tank. See 1926.154(e)(4).

• Verify the heater’s approval or listing that authorizes an external tank connection and document that approval on site.
• If the heater is not so approved, use the integral tank or an approved fuel-delivery system.

The employer (or the party controlling the worksite) is responsible for ensuring temporary heating devices are installed to meet the clearance and mounting requirements in 1926.154(b).

• Employers should perform a hazard assessment before using heaters, select appropriate heaters, and document compliance with clearances and mounting requirements; OSHA guidance on employer hazard assessments and PPE selection is helpful (LOI 2024-03-28).
• Keep manufacturer instructions, listing approvals, and on-site measurements available to demonstrate proper installation.

You should monitor for combustion hazards (at minimum carbon monoxide and oxygen levels) and use appropriate ventilation controls whenever combustion heaters are used in confined or occupied spaces, as required by 1926.154(a)(2).

• Install continuous carbon monoxide (CO) monitors with alarms and portable or fixed oxygen monitors where combustion and fresh-air supply may be limited.
• Document the monitoring plan and results as part of the job hazard assessment; OSHA’s PPE/hazard-assessment interpretation explains employer responsibilities for hazard assessments (LOI 2024-03-28).

Temporary heaters may be used on scaffolds only if they comply with the general clearance and mounting rules in 1926.154(b), but solid fuel salamanders are expressly prohibited on scaffolds by 1926.154(d).

• Ensure the heater used on a scaffold is rated for that use, positioned level, meets the required clearances from combustibles, and rests on noncombustible or insulating support as required by 1926.154(b)(3).
• Avoid heaters that can tip or spill fuel; follow manufacturer’s scaffold-use instructions and keep documentation on site.

The required minimum clearance to a chimney connector is 18 inches for both circulating room heaters and radiant room heaters. See 1926.154(b)(1) and Table F-4.

• Verify chimney connectors and venting meet the 18-inch clearance and follow manufacturer venting instructions if they allow different clearances (see 1926.154(b)(2)).

If the heater is listed and approved for installation with smaller clearances, you may follow the manufacturer’s listing and approval instead of Table F-4. See 1926.154(b)(2).

• Maintain the listing/approval documentation and the manufacturer’s installation instructions to show why the reduced clearance was used.
• Do not rely on verbal manufacturer guidance—use the formal listing or approval paperwork.

Heaters not suitable for wood floors must rest on suitable heat-insulating material or at least 1-inch concrete (or equivalent), and the insulating material must extend at least 2 feet beyond the heater in all directions. See 1926.154(b)(3).

• "Suitable heat-insulating material" should be selected based on manufacturer guidance or vendor specifications showing it prevents heat transfer to combustibles.
• The protective base must extend a minimum of 2 feet beyond the heater footprint on every side.

Coverings must be securely fastened so wind cannot blow them onto or otherwise upset the heater, and heaters must be located at least 10 feet from the coverings, per 1926.154(b)(4).

• Use ties, anchors, or rigid supports to prevent flapping or displacement of tarps and canvas.
• Re-locate the heater or the covering if secure fastening cannot prevent contact or tipping under expected wind conditions.

Heaters designed for barometric or gravity oil feed must be used only with their integral tanks and barometric/gravity feed is not considered a primary safety control; heaters that require connection to separate tanks must be specifically designed and approved for that configuration. See 1926.154(e)(1), 1926.154(e)(2), and 1926.154(e)(4).

• Do not rely on barometric/gravity feed as a safety shutoff; use heaters with active primary safety controls that stop fuel if the flame fails.
• If you wish to use an external tank, confirm the heater’s approval for separate supply tanks and keep that approval documentation available.

Yes — employers must assess the workplace for hazards associated with temporary heating (ventilation needs, combustion byproducts, heat stress, fire risk) before selecting controls and PPE, consistent with 1926.154(a) and OSHA’s hazard-assessment interpretation (LOI 2024-03-28).

• The hazard assessment should identify air contaminants (CO), oxygen deficiency, ignition/fire hazards, and heat stress, then select controls (ventilation, safe heater type/placement) and any necessary PPE.
• When PPE is required, employers must document the hazard assessment and provide appropriate PPE at no cost per OSHA guidance.