Temporary Heaters

Temporary heaters keep work going in winter and help concrete cure, but they start fires and produce carbon monoxide in enclosed areas. Heater fires and CO poisonings on construction sites often happen overnight, when no one is there to notice. Choosing the right heater, setting it up correctly and watching it every hour it runs prevents most of these incidents.

• Construction

Types of temporary heaters

What OSHA says

OSHA’s temporary heating rules for construction are in 29 CFR 1926.154, and rules for liquefied petroleum gas (LPG) are in 1926.153. Highlights in plain language (check the standards for full detail):

• Fresh air: enough fresh air must be supplied to maintain the health and safety of workers. Where natural ventilation is not enough, mechanical ventilation must be provided.
• Clearance: heaters must be installed with the clearance from combustible material shown on the manufacturer’s approval plate or listing.
• Tarps and coverings: heaters near tarpaulins, canvas or similar coverings must be placed a safe distance from them (OSHA specifies a minimum distance, such as 10 feet), and coverings must be securely fastened so they can’t ignite or fall onto the heater.
• Solid-fuel salamanders are prohibited in buildings and on scaffolds.
• Heaters must be stable, with a means to prevent them from tipping or upsetting, and set on a firm base.
• Fuel-fired heaters need safety controls, such as a flame failure shutoff and a means to stop the flow of fuel, as the standard describes.
• Liquid fuel heaters must be refueled with the heater off and cool and kept away from ignition.
• LPG containers and connections must be protected and positioned as the LPG rules and the maker direct. See Propane and Compressed Gas Cylinders.

Set-up

• Use heaters approved and listed for construction use, following the manufacturer’s clearance distances
• Keep them away from tarps, wood, insulation, fuel and other combustibles, including temporary protection materials, plastic sheeting and stacked materials
• Set on a level, noncombustible surface. Protect wood floors per the manufacturer.
• Provide ventilation in enclosed or tented areas, and monitor carbon monoxide
• Propane cylinders positioned and connected per the manufacturer, outside the heater’s heat path, and secured upright
• Fire extinguisher nearby. See Fire Extinguishers (PASS)
• Flame-retardant tarps and enclosure materials, and openings for intake and exhaust air
• Hoses and regulators protected from damage, with connections tested for leaks using soapy water, never a flame

Rules

• Don’t use solid-fuel salamanders (burning wood or coal) inside buildings or on scaffolds.
• Don’t leave heaters running unattended unless designed for it.
• Don’t refuel kerosene or diesel heaters while running or hot.
• Don’t use them to dry clothing or gloves.
• Don’t use a heater inside a tent, trailer or room with no ventilation, and don’t block the air intake or exhaust.
• Don’t use gasoline in a heater made for kerosene or diesel, or the wrong fuel for any heater.
• Don’t move a heater while it’s running or hot, or leave it on a scaffold plank or unstable spot.
• Don’t run a cord or hose where it can be damaged, or overload circuits with electric heaters. See Extension Cords and Temporary Power.

Carbon monoxide in more detail

• CO is a colorless, odorless gas that blocks oxygen in the blood. OSHA’s permissible exposure limit is 50 parts per million averaged over 8 hours, and much lower levels cause symptoms over time. Higher levels can kill in minutes.
• Symptoms: headache, dizziness, nausea, weakness, confusion, shortness of breath, drowsiness. Workers may mistake it for the flu or tiredness, and people can pass out and die without noticing.
• Use CO monitors with alarms in areas with fuel-burning heaters, and check that they work and are calibrated. See Gas Detectors.
• Ventilate with fresh air and exhaust. Make sure fresh air intakes aren’t near exhaust. Prefer indirect-fired heaters vented outdoors, or electric heaters, in enclosed areas.
• If an alarm sounds or anyone has symptoms: shut off the heater, open doors and windows, get everyone to fresh air, and call 911. Don’t send people back in until the air tests safe.

Fire prevention

• Watch the surroundings: sawdust, plastic sheeting, insulation, paper, tarps and building materials can ignite from radiant heat or direct flame. Keep a clear zone around the heater.
• Keep fuel safe: store fuel and cylinders outside, away from the heater, and secure them upright. Don’t refuel inside the enclosure. See Fuel Storage Tanks on Jobsites and Flammable Liquids.
• Plan for the night. Many fires start overnight. If a heater must run unattended, use a heater designed for it with automatic safety shutoffs, put someone on fire watch, or shut it down at the end of the shift, as your plan and the fire marshal allow.
• Set up heated enclosures and tents with flame-retardant material, exits and vents. See Jobsite Fire Prevention and Exit Routes.
• Check for tip-over switches, flame sensors and thermostats before use. Test them regularly.
• Know where the fuel shutoff is. If a heater catches fire, shut off the fuel if you can do so safely, use an extinguisher on a small fire, and evacuate and call 911 for anything larger.

Heating concrete and winter work

• Heaters help concrete cure in cold weather. Direct-fired heaters can cause surface problems in fresh concrete from carbon dioxide, and they create CO hazards in enclosures, so use indirect-fired heaters or vented systems where possible.
• Cold weather brings other hazards: ice, slips and cold stress. See Cold Stress and Slips, Trips & Falls.
• Heaters near scaffolds and tarped structures need a competent person’s review. See Scaffolds in Wind, Rain & Ice.

Electric heaters

• Plug into circuits sized for the load, and use heavy-duty extension cords rated for the amperage, as short as possible, fully uncoiled. Don’t daisy-chain cords or use damaged ones.
• Use GFCI protection. See GFCI.
• Keep electric heaters clear of combustibles and don’t cover them.

Training

Anyone who sets up, fuels or works near temporary heaters should know the hazards, the clearances, the shutoffs and the CO warning signs. See Training Requirements and Emergency Action Plans.

Heater checklist

• Heater is listed for construction use and set up at the required clearances
• Tarps and combustibles are well away; enclosures use flame-retardant material
• Ventilation is adequate; CO monitor is working
• Fuel and cylinders are stored and connected as required and leak-tested
• Extinguisher in place; fire watch or shutdown plan for after hours
• No salamanders inside buildings or on scaffolds; no refueling while hot

Last updated: October 4, 2026