Portable generator carbon monoxide controls on a jobsite

Treat exhaust as a life-threatening hazard

Portable generators burn fuel and produce carbon monoxide (CO), a colorless, odorless gas that can overcome workers without warning. Construction sites create common exposure conditions: temporary enclosures, winter weatherproofing, basements, garages, crawl spaces, partially completed buildings, and generators placed near an air intake. CO can accumulate even when a door is open or a room appears ventilated. Smell is not a reliable warning, and headache or dizziness may be mistaken for fatigue.

OSHA advises that portable generators never be used indoors or in enclosed spaces such as garages, crawl spaces, or basements. Use them outdoors and keep them away from doors, windows, and ventilation openings where exhaust can enter. OSHA’s generator alert recommends at least 3 to 4 feet of clear space on all sides and above the generator for ventilation; always follow the machine manufacturer’s instructions and local fire requirements as well.

Choose the location before starting the generator

Locate the generator outside the building footprint, with exhaust directed away from workers and occupied areas. Consider wind direction, neighboring structures, courtyards, loading docks, air intakes, windows, and temporary plastic walls. A generator placed outside can still send exhaust into a building through a door or mechanical intake. Reassess the location if the wind changes, the enclosure is tightened, or temporary partitions are added. Do not place a generator in a loading bay and assume the large opening provides adequate dilution.

Keep the required space around the generator clear of combustible materials and obstructions. Protect the unit from rain using only approved arrangements that do not trap exhaust or block cooling airflow. Refuel outdoors after shutdown and cooling, and store fuel in approved containers in the designated area. Keep the generator dry, inspect it for damage or loose fuel lines, and operate it according to its manual. Carbon monoxide control does not replace electrical safety, grounding, GFCI, or fire prevention requirements.

Avoid running fuel-powered equipment inside

Generators are not the only CO source. Gasoline-powered saws, compressors, pumps, forklifts, heaters, and other combustion equipment can expose workers in semi-enclosed areas. Whenever practical, choose electric or battery-powered equipment for indoor work. If combustion equipment must operate, the employer needs an effective ventilation and exposure-control plan appropriate to the space and equipment. Opening a window or rolling up a door is not a substitute for evaluating airflow and exposure.

CO monitors with audible alarms can provide another layer of warning where a potential hazard exists, but they do not make an unsafe generator location acceptable. Select and place monitors according to their instructions and the site hazard assessment. Assign someone to respond to an alarm, evacuate affected workers, and prevent re-entry until trained and properly equipped personnel determine the area is safe. Never send an unprotected coworker back inside to rescue someone overcome by CO.

A monitor should be selected for the exposure conditions and used according to its maker’s guidance; one detector at a distant entrance may not represent air where workers are cutting or operating equipment. Decide who checks alarms, how the crew accounts for everyone, and which safe exterior assembly point to use. Never silence or relocate an alarm because it disrupts the task. If a detector alarms or a worker becomes symptomatic, stop the source only from a safe location and call trained responders.

Recognize symptoms and respond immediately

Early symptoms of CO exposure can include headache, dizziness, weakness, nausea, vomiting, chest tightness, and drowsiness. Confusion, collapse, loss of consciousness, and death can follow severe exposure. If a worker develops symptoms, move the person to fresh air immediately if it is safe to do so, call emergency services, and obtain medical attention. Do not re-enter the area to retrieve equipment or help another worker unless the rescue team is trained and equipped for the atmosphere.

A symptom report should trigger a work-area response, not just a rest break. Shut down or isolate the fuel source only if that can be done without entering the hazardous area. Evacuate workers, identify other potentially exposed people, and have the area assessed. Because CO has no odor, an area that seems normal after the generator stops may still need to be checked. Document the event, the generator location, ventilation conditions, monitoring results, and corrective actions.

Plan for temporary power and building phases

Temporary-power plans should identify generator locations, cord routes, protected receptacles, fuel storage, exhaust direction, and fire access. Coordinate generator placement with site logistics so it is not moved into an enclosed area as work progresses. Before installing temporary walls, shrink wrap, or winter enclosures, review whether existing combustion sources remain outside and whether air intakes could draw in exhaust. Include subcontractors who bring their own generators; the hazard crosses trade boundaries.

During renovation, occupied areas need special attention. An exterior generator can contaminate return air, a vestibule, or a loading door. Coordinate shutdown and relocation when the building’s air-handling pattern changes. Keep a reliable communication plan so workers know the generator location, alarm response, evacuation route, and emergency contact. A brief pre-task review is particularly important when a generator powers equipment inside a basement or near an enclosed work area.

Example: winter interior demolition

A crew uses a portable generator to power tools in a basement during winter. The basement door is propped open, but the generator sits on the landing just outside it and its exhaust drifts down the stairwell. This is not a safe indoor-use workaround. Move the generator well outdoors, away from doors and air openings, or switch to electric power supplied from a safe external source. If workers experienced symptoms, evacuate, call emergency services, and have the area evaluated before returning.

A simple generator-control checklist

• Place the generator outdoors, away from openings and air intakes; direct exhaust away from people.
• Keep 3 to 4 feet clear around and above the unit, or follow greater manufacturer clearance.
• Inspect for damage and leaks; refuel only after shutdown and cooling.
• Use CO monitoring only as an added control, with an alarm-response plan.
• Prefer electric or battery-powered equipment indoors.
• Evacuate and seek emergency help for suspected exposure; do not re-enter without assessment.