Petrol, diesel and LPG generators can provide essential power during an outage, on a construction site, at an event or in a remote location. However, every generator powered by a combustion engine produces exhaust gases containing carbon monoxide.

Carbon monoxide, commonly shortened to CO, is a highly poisonous gas. It has no colour, smell or taste, which means people cannot rely on their senses to detect it.

A generator should never be operated inside a house, garage, shed, warehouse, tent, caravan, vehicle or other enclosed or partly enclosed space. Carbon monoxide can accumulate rapidly and may cause serious illness, permanent injury or death.

Opening a window, lifting a garage door or using a domestic fan does not make indoor generator operation safe. The generator must be positioned outdoors where its exhaust gases can disperse and cannot enter an occupied building.

This guide explains how generator carbon monoxide is produced, where the main risks occur, how to position a generator safely and what action to take if exposure is suspected.

What Is Carbon Monoxide?

Carbon monoxide is a poisonous gas produced when carbon-based fuels do not burn completely.

Fuels capable of producing carbon monoxide include:

Petrol
Diesel
LPG and propane
Natural gas
Coal
Wood
Charcoal
Heating oil

A generator engine burns fuel to produce mechanical power. The engine turns an alternator, which produces electricity. Exhaust gases created during combustion are then discharged through the generator’s exhaust system.

Even a correctly maintained generator can produce carbon monoxide during normal operation. Carbon monoxide safety is therefore not limited to old, damaged or badly running machines.

Why Is Carbon Monoxide Dangerous?

When carbon monoxide is breathed in, it interferes with the blood’s ability to carry oxygen around the body.

The brain, heart and other organs can quickly become deprived of oxygen. Exposure may cause illness before the affected person realises that carbon monoxide is present.

The seriousness of exposure depends on factors including:

The concentration of carbon monoxide
The length of exposure
The person’s activity level
The size and ventilation of the area
The person’s age and general health
Whether the person is asleep

High concentrations can cause collapse or death very quickly. Lower concentrations may cause symptoms over a longer period.

Why Generators Create a Particular Carbon Monoxide Risk

Generators are often used when normal services are unavailable, such as during storms, flooding, power cuts or emergency building work.

In these situations, users may be tempted to place the generator somewhere they believe is protected from weather or theft.

Dangerous locations can include:

Inside a garage with the door open
Inside a shed
Under a carport
Inside a loading bay
Inside a warehouse doorway
Under a gazebo with side panels
Inside an awning
Inside a tent or marquee
Inside a van or trailer
In a basement or below-ground area

These spaces may appear ventilated but can still allow exhaust gases to collect or enter nearby occupied areas.

Do Petrol Generators Produce Carbon Monoxide?

Yes. All engine-driven petrol generators produce carbon monoxide in their exhaust gases.

Small portable petrol generators can be particularly dangerous when used incorrectly because they are easy to carry into garages, sheds, workshops and other enclosed spaces.

Their compact size does not make them safe for indoor use. A small engine can still produce a dangerous concentration of carbon monoxide in a confined area.

Do Diesel Generators Produce Carbon Monoxide?

Yes. Diesel generators also produce carbon monoxide and other harmful exhaust emissions.

Diesel exhaust may have a strong smell, but smell is not a reliable indication of carbon monoxide concentration. Carbon monoxide itself cannot be seen or smelled.

Portable and industrial diesel generators must be positioned so that exhaust gases cannot collect or enter occupied buildings.

A permanently installed diesel generator may use a professionally designed exhaust system, but the complete installation still requires suitable ventilation, cooling airflow and safe exhaust discharge.

Do LPG Generators Produce Carbon Monoxide?

Yes. An LPG generator can still produce dangerous carbon monoxide.

LPG may burn more cleanly than some other fuels, but this does not make an LPG-powered generator suitable for indoor use.

Carbon monoxide can be produced whenever fuel is burned. Poor ventilation, incorrect combustion, damaged equipment or restricted airflow can increase the risk further.

Do Inverter Generators Produce Carbon Monoxide?

Yes. Inverter generators powered by petrol or another combustion fuel produce carbon monoxide in the same way as conventional engine-driven generators.

Their quieter operation can create an additional risk because people may underestimate the danger or forget that the generator is running.

An inverter generator must remain outdoors even when it is:

Small
Quiet
Operating in eco mode
Running at a low load
Fitted with an enclosed casing

Do Silent Generators Produce Carbon Monoxide?

A silent generator is not emission-free.

The word silent normally refers to an acoustic enclosure designed to reduce engine and exhaust noise. It does not mean that the generator produces no exhaust gases.

Acoustic enclosures contain carefully designed cooling-air and exhaust routes. These must not be blocked or modified.

Silent generators must still be installed outdoors or within a purpose-designed generator room that has been professionally engineered for ventilation, cooling and exhaust extraction.

Are Open-Frame Generators More Dangerous?

An open-frame generator is not automatically more poisonous than an enclosed generator, but its exposed engine and exhaust can make correct positioning especially important.

Open-frame models are commonly used on construction sites, farms, workshops and for emergency backup.

They should never be moved indoors simply to reduce noise, protect them from rain or prevent theft.

Can a Three-Phase Generator Produce Carbon Monoxide?

Yes. The electrical output does not affect whether an engine produces carbon monoxide.

A three-phase generator powered by petrol, diesel, LPG or natural gas produces combustion exhaust in the same way as a single-phase generator.

Larger three-phase generator sets may produce a substantial volume of exhaust gas and heat. Their installation may require:

A professionally designed exhaust system
Mechanical ventilation
Cooling-air calculations
Fire-resistant materials
Carbon monoxide detection
Safe discharge away from building openings

Can I Run a Generator in a Garage With the Door Open?

No. A generator should not be operated inside a garage, even when the main door is fully open.

Exhaust gases can remain trapped inside the structure, spread into the connected property or be drawn through doors, windows and ventilation systems.

Wind direction can also push fumes back into the garage or house.

A partially open garage door, side door or window does not provide reliable protection.

Can I Run a Generator in a Shed?

A portable generator should not be operated inside an ordinary garden shed, storage shed or workshop.

Opening the shed door is not enough to guarantee safe ventilation. Carbon monoxide and heat can still accumulate.

A shed can also create additional hazards, including:

Fire from hot exhaust components
Ignition of stored fuel
Engine overheating
Restricted cooling airflow
Damage to the generator
Exhaust gases entering nearby buildings

Can I Use a Generator in a Warehouse or Workshop?

A generator should not be operated inside a warehouse or workshop simply because the building is large.

Carbon monoxide can accumulate in local areas, particularly where doors are closed, air movement is poor or exhaust gases collect around workstations.

HSE guidance warns that petrol-powered equipment can create dangerous carbon monoxide levels within minutes when used indoors or in enclosed spaces.

Where a commercial operation genuinely requires a combustion engine within a structure, the risk must be professionally assessed and controlled using purpose-designed ventilation or extraction. Normal doors, windows and domestic fans should not be relied upon.

Can I Run a Generator Under a Canopy?

A generator requires protection from unsuitable weather conditions, but a canopy must not create an enclosed or poorly ventilated area.

Avoid structures with side panels, walls or low roofs that could trap exhaust gases or redirect them towards people and buildings.

Any weather cover should:

Be specifically suitable for generator use
Provide unrestricted cooling airflow
Keep exhaust gases clear of the enclosure
Use heat-resistant materials
Maintain safe clearances from the exhaust
Not allow fumes to collect underneath

Do not place a plastic sheet, tarpaulin or improvised box directly over a running generator.

How Far Should a Generator Be From a Building?

The generator should be positioned outdoors and well away from:

Doors
Windows
Air bricks
Extractor fans
Boiler flues
Roof vents
Mechanical air intakes
Neighbouring buildings

There is no single distance that guarantees safety in every location because the correct position depends on the generator, building design, wind direction and surrounding structures.

Follow the generator manufacturer’s minimum-clearance instructions and increase the distance where practical.

The exhaust outlet should face away from occupied areas and building openings.

Why Wind Direction Matters

Exhaust gases do not always travel in a straight line away from the generator.

Wind can:

Carry fumes towards an open window
Blow exhaust under a canopy
Push gases into a garage or doorway
Cause fumes to collect behind a wall
Move gases towards neighbouring properties

Generator positioning should be checked whenever weather conditions change.

Do not assume that a position is safe simply because the exhaust appeared to travel away from the building when the generator was first started.

Can Exhaust Enter Through Closed Windows?

Closed windows reduce direct airflow but do not necessarily create an airtight barrier.

Exhaust gases may enter through:

Window seals
Air vents
Extractor-fan openings
Doors
Roof spaces
Wall cavities
Service penetrations

The safest approach is to position the generator well away from the building rather than relying on closed windows alone.

Can I Use a Fan to Remove Generator Fumes?

A normal domestic or workshop fan does not make indoor generator use safe.

A fan may move exhaust gases unpredictably, spread them into other rooms or fail if the generator stops supplying power.

Purpose-designed mechanical extraction may be used in specialist commercial generator installations, but it must be professionally calculated and installed.

Portable generator users should place the generator outdoors rather than attempting to ventilate an unsuitable indoor location.

Can I Smell Generator Exhaust Before It Becomes Dangerous?

Generator exhaust may have a noticeable smell, but carbon monoxide itself is odourless.

The strength of the exhaust smell does not indicate whether the carbon monoxide concentration is safe.

A person may also become less aware of a smell after being exposed to it for a period of time.

Never use smell as a substitute for safe positioning and a working carbon monoxide alarm.

Symptoms of Carbon Monoxide Poisoning

Carbon monoxide poisoning can be difficult to recognise because early symptoms resemble flu, tiredness, a viral illness or food poisoning.

Possible symptoms include:

Headache
Dizziness
Feeling sick or vomiting
Weakness
Unusual tiredness
Confusion
Shortness of breath
Chest pain
Stomach pain
Loss of coordination
Visual problems
Collapse
Loss of consciousness
Seizures in severe cases

Symptoms may become worse while a person is inside the affected area and improve after going outdoors.

More than one person becoming unwell at the same time is an important warning sign. Pets may also show symptoms before humans.

Who Is Most at Risk?

Carbon monoxide can affect anyone, but some people may be more vulnerable to its effects.

Higher-risk groups can include:

Babies and young children
Pregnant women and unborn babies
Older people
People with heart conditions
People with breathing conditions
People who are asleep
People carrying out physical work

A sleeping person may not recognise early symptoms or hear activity associated with the generator.

What Should I Do If I Suspect Carbon Monoxide Poisoning?

If a carbon monoxide alarm sounds, anyone develops possible symptoms or generator fumes may be entering a building:

Move everyone into fresh air immediately.
Leave the affected building or enclosed area.
Do not delay evacuation to investigate the source.
Call 999 where anyone has collapsed, is unconscious, has difficulty breathing or is seriously unwell.
Seek urgent medical advice and state that carbon monoxide exposure is suspected.
Do not return until the source has been made safe and professional advice confirms that it is safe.

Switch off the generator only when this can be done safely from fresh air without delaying evacuation or placing anyone at further risk.

Symptoms may improve after leaving the area, but medical advice should still be obtained because carbon monoxide exposure can cause serious effects.

Do I Need a Carbon Monoxide Alarm When Using a Generator?

A working audible carbon monoxide alarm provides an important additional warning if exhaust gases enter an occupied building.

An alarm does not make it safe to operate a generator indoors, in a garage or close to a window.

Safe generator positioning remains the primary protection.

A suitable alarm should:

Be audible
Meet the appropriate recognised standard
Be obtained from a reputable supplier
Be positioned according to the manufacturer’s instructions
Be tested regularly
Have its batteries replaced where required
Be replaced at the end of its stated service life

Alarms for caravans, boats and similar leisure accommodation may require certification to a standard suitable for those environments.

Where Should a Carbon Monoxide Alarm Be Positioned?

Follow the alarm manufacturer’s installation instructions because positioning varies according to the alarm type and room.

The alarm should be located where it can be heard by occupants, including people who are asleep.

Do not place an alarm:

Where furniture or curtains block it
Inside a cupboard
Immediately beside a ventilation opening
In an unsuitable damp or dusty position
Outside its approved temperature range

A carbon monoxide alarm should never be placed outdoors beside the generator as a substitute for alarms protecting occupied areas.

Will a Smoke Alarm Detect Carbon Monoxide?

A standard smoke alarm does not detect carbon monoxide unless it is specifically described as a combined smoke and carbon monoxide alarm.

Smoke and carbon monoxide are different hazards and require suitable detection technology.

Check the alarm label and instructions rather than assuming that any audible household alarm provides carbon monoxide protection.

What Should I Do If the Carbon Monoxide Alarm Sounds?

Never ignore or silence a carbon monoxide alarm without taking action.

If the alarm sounds:

Move everyone into fresh air immediately.
Call emergency services if anyone is unwell.
Stop using the generator when it is safe to do so.
Do not re-enter the affected area merely because the alarm stops.
Have the source and affected building assessed before further use.

Do not assume that the alarm is faulty because you cannot smell fumes.

Can I Run a Generator Overnight?

A generator should only run overnight when it is suitable for extended operation and has been positioned safely outdoors.

Overnight operation creates additional concerns because:

Occupants may be asleep when fumes enter
Wind direction may change
Fuel or mechanical faults may go unnoticed
The generator may be left unattended
A carbon monoxide alarm must be loud enough to wake occupants

Before overnight operation, confirm that:

The generator is well away from buildings
The exhaust faces away from occupied areas
Suitable carbon monoxide alarms are working
The generator is protected from unauthorised access
The unit is suitable for the expected running period
Fuel capacity is sufficient
The generator will not require hot refuelling

Can I Use a Generator Near a Tent or Caravan?

Generators should be positioned well away from tents, awnings, caravans, motorhomes and boats.

These spaces may have openings close to sleeping areas, and fabric structures offer little protection against exhaust gases.

Never operate a generator:

Inside a tent
Inside an awning
Inside a caravan
Inside a motorhome
Inside a boat cabin
Under attached fabric shelters

Position the generator so that prevailing winds cannot carry fumes towards neighbouring pitches or accommodation.

Carbon Monoxide Safety at Events

Events may use generators close to marquees, food stalls, stages, temporary buildings and public walkways.

Event planning should consider:

Exhaust direction
Distance from tents and marquees
Changes in wind direction
Public access
Staff work areas
Ventilation around catering units
Carbon monoxide alarms
Emergency shutdown arrangements

A generator should not be placed behind a stall or inside a catering tent simply to hide noise or prevent theft.

Carbon Monoxide Safety on Construction Sites

Construction work can involve generators, cut-off saws, pumps and other petrol-powered equipment.

Carbon monoxide risks may arise in:

Buildings under construction
Basements
Excavations
Trenches
Temporary enclosures
Containers
Partly completed rooms

A space does not need to be completely sealed for dangerous carbon monoxide concentrations to develop.

Where possible, use mains-powered, battery-powered or hydraulically powered equipment instead of a combustion engine within an enclosed work area.

Employers must assess and control exposure risks and may require specialist ventilation, monitoring and supervision.

Carbon Monoxide Safety During Flood Recovery

Generators are sometimes used to power pumps, heaters and dehumidifiers after flooding.

The generator itself must remain outdoors even when the equipment being powered is inside the property.

Use suitable outdoor-rated cables and ensure that electrical connections remain protected from water.

Never place a generator inside a damaged or unoccupied property on the assumption that no one will be exposed. Exhaust gases can enter neighbouring buildings or affect workers who later enter the area.

Can Generator Exhaust Be Extended With a Hose?

Do not attach an improvised hose or pipe to a portable generator exhaust.

An unsuitable exhaust extension can:

Leak carbon monoxide
Create excessive back pressure
Overheat
Cause a fire
Damage the engine
Redirect fumes unpredictably

Exhaust extensions should only be used where they form part of a system designed or approved by the generator manufacturer and installed by a competent professional.

Does Generator Maintenance Reduce Carbon Monoxide?

Correct maintenance helps the engine operate as intended, but it does not eliminate carbon monoxide production.

Maintenance should include:

Checking and changing engine oil
Cleaning or replacing air filters
Inspecting the exhaust system
Checking fuel systems
Maintaining the correct engine speed
Checking cooling-air passages
Following manufacturer service intervals

Stop using the generator if the exhaust system is damaged, loose or leaking.

Black smoke, poor running or unusual exhaust deposits may indicate a fault, but the absence of visible smoke does not prove that the exhaust is safe.

Can I Leave a Generator Unattended?

Portable generators should be checked regularly during operation.

Inspections can identify:

Changes in wind direction
Exhaust leaks
Blocked cooling openings
Fuel leaks
Overheating
Movement caused by vibration
Unauthorised interference

A fixed standby generator may be designed for automatic operation, but it still requires professional installation, maintenance and routine testing.

Generator Placement Checklist

Before starting a generator, confirm that it is:

Outdoors
Well away from doors and windows
Clear of air intakes and vents
Positioned with its exhaust facing away from buildings
Not inside a garage, shed or warehouse
Not under an enclosed canopy
Standing on a stable surface
Protected from unsuitable weather without restricting ventilation
Clear of dry vegetation and combustible materials
Protected from children and unauthorised users

Recheck the position if wind direction or site conditions change.

Generator Carbon Monoxide Safety Checklist

Read the manufacturer’s operating instructions
Never operate a fuel-powered generator indoors
Never use a generator in a partly enclosed area
Keep the generator well away from occupied buildings
Point the exhaust away from doors, windows and vents
Install suitable audible carbon monoxide alarms
Test alarms according to their instructions
Do not rely on smell to detect carbon monoxide
Do not use domestic fans as exhaust extraction
Do not improvise an exhaust extension
Maintain the generator correctly
Stop using equipment with a damaged exhaust
Move into fresh air immediately if exposure is suspected
Call 999 where anyone is seriously unwell, unconscious or has collapsed

Choosing a Safer Generator

No combustion-engine generator is safe for indoor operation, but certain features can help improve safety when the unit is used correctly.

Useful features may include:

Automatic carbon monoxide shutdown technology
Low-oil shutdown
Overload protection
Clearly directed exhaust outlets
Suitable weather protection
Remote monitoring on standby models
Automatic fault shutdown

Carbon monoxide shutdown technology is an additional safety feature. It does not permit the generator to be operated indoors or close to occupied buildings.

Can a Battery Power Station Be Used Indoors?

A battery power station does not burn petrol, diesel or LPG during operation and therefore does not produce engine exhaust or carbon monoxide.

For small indoor loads, a suitable battery-based system may provide a safer alternative to operating a combustion generator nearby.

Battery systems still require correct charging, ventilation where specified, electrical protection and compliance with the manufacturer’s instructions.

When Should Professional Advice Be Obtained?

Professional advice is recommended where a generator will:

Be permanently installed
Operate close to a building
Use an extended exhaust system
Be installed inside a purpose-built generator room
Supply a business or industrial facility
Operate automatically without supervision
Power an event or public area
Be used within a complex construction environment

The installation may require assessment by generator engineers, ventilation specialists, electrical contractors and fire-safety professionals.

Conclusion

Every petrol, diesel and LPG generator produces carbon monoxide in its exhaust gases.

Carbon monoxide cannot be seen, smelled or tasted, and dangerous levels can build quickly in enclosed and partly enclosed areas.

A portable generator must never be operated inside a house, garage, shed, warehouse, tent, caravan, vehicle or other enclosed structure. Opening doors and windows or using a fan does not make indoor operation safe.

Position the generator outdoors, well away from doors, windows, vents and occupied areas. Point the exhaust away from buildings and reconsider the position whenever wind conditions change.

Install suitable audible carbon monoxide alarms as an additional warning, but never use an alarm as a substitute for safe generator positioning.

If an alarm sounds or carbon monoxide exposure is suspected, move everyone into fresh air immediately, seek medical help and call 999 where anyone is seriously unwell, unconscious or has collapsed.

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