Carbon monoxide alarms and gas detectors are often mentioned in the same breath when it comes to home safety, and it is easy to assume that one device might do both jobs. In fact they detect entirely different hazards and use different sensor technologies. Having a carbon monoxide alarm does not protect you against a gas leak, and a gas detector does not protect you against carbon monoxide poisoning.

What Carbon Monoxide Detectors Detect

Carbon monoxide, or CO, is a colourless, odourless gas produced when fuels are burned incompletely. It is generated by boilers, gas fires, cookers, wood burners, open fires, and petrol or diesel engines when they are malfunctioning, poorly ventilated, or have blocked flues. A carbon monoxide alarm is specifically designed to detect the presence of CO in the air and trigger an alert when the concentration reaches a dangerous level.

Carbon monoxide is produced by the combustion of a fuel. Natural gas or LPG that leaks from a pipe or appliance without being ignited does not produce CO. A gas leak and CO poisoning are therefore two separate hazards with separate causes.

What Natural Gas and LPG Detectors Detect

A natural gas detector, sometimes called a gas leak detector or combustible gas detector, is designed to detect the presence of methane, which is the primary component of natural gas, or propane and butane, which are the components of LPG. These detectors alert you to a gas leak before the concentration in the air becomes high enough to ignite. Natural gas and LPG are both highly flammable and create a risk of fire or explosion if they accumulate in an enclosed space and reach an ignition source.

Natural gas has an odorant, mercaptan, added to it specifically so that leaks can be detected by smell. LPG similarly has odorant added. However, not all people can reliably detect small or gradual leaks by smell, particularly in large or well-ventilated spaces, which is why gas detectors add an objective level of protection.

Combination Detectors

Some devices are marketed as combination alarms that detect both carbon monoxide and natural gas or combustible gases in one unit. These use different sensor technologies within the same housing and provide both types of detection. If you want a single device to cover both hazards, look specifically for a combination CO and gas alarm rather than assuming that either type of single-function alarm covers both.

Where to Position Each Detector

Carbon monoxide is slightly lighter than air, but the difference is small and CO detectors are generally positioned at head height or higher, at least a metre from any fuel-burning appliance, and in the room where the appliance is situated and in sleeping rooms. Natural gas, being lighter than air, tends to accumulate near the ceiling. Natural gas detectors should therefore be positioned higher up, near the ceiling, in rooms containing gas appliances or where gas pipework runs.

What to Do If Either Alarm Triggers

If a carbon monoxide alarm sounds, stop using all fuel-burning appliances, open windows and doors, leave the building immediately, and call the Gas Emergency Service on 0800 111 999 if the alarm is related to a gas appliance, or seek medical advice if anyone is showing symptoms of CO poisoning including headache, dizziness, or nausea. If a gas leak detector sounds, do not operate any electrical switches, open windows and doors, leave the building, and call the Gas Emergency Service from outside the building.

Summary

Carbon monoxide detectors do not detect natural gas or LPG leaks. They detect CO, which is a combustion byproduct produced when fuels burn incompletely. Gas leak detectors detect flammable gas in the air before it reaches ignition concentration. Both hazards are serious but distinct, and protecting against both requires appropriate detectors for each. Combination units that detect both CO and gas are available and provide comprehensive coverage in a single device.