Are your carbon monoxide alarms protecting you enough? How I discovered a carbon monoxide leak that monitors missed

A recent visit to a friend's home reminded me that while we all put confidence in our carbon monoxide and smoke alarms alerting us to danger, the reality is they may not be quite as effective as we think.

So what levels should they be detecting, and how can you make sure yours are working as they should?

Using my real-life experience of what happens when carbon monoxide is leaking into a home I explain what you really need to consider when purchasing, installing and maintaining your carbon monoxide and smoke alarms.

How I knew something was wrong

I recently visited a friend's home and after a few hours I started feeling a headache coming on. I went outside for fresh air and it cleared. An hour or so later it came back.

I thought it might be dehydration, but once again when I went outside it cleared which made me curious. I went to the car and got my air quality analyser as I often keep various tools in the car, even when I am not at work in my role as a renewables and ventilation installer.

I tested the air in the living room, and the carbon monoxide (CO) reading was 47ppm (parts per million). To put this into context, while the ideal number is zero, the World Health Organisation (WHO) recommends maximum levels of 9 – 10 ppm over an eight-hour period.

What carbon monoxide levels mean

CO is often referred to as the ‘silent killer’ because it is completely invisible, has no smell or taste, and can cause severe poisoning or death before a person even realises it is there. CO enters the blood through the lungs and stops oxygen from reaching vital organs like the heart and brain.

The levels the monitor was reading in the home I was visiting were clearly above the recommended standard, but what do the levels mean and what can you expect to happen if you are in an environment where they are higher?

• 0 – 9ppm: Normal background levels, deemed safe for continuous exposure
• 10 – 35ppm: Elevated level. Prolonged exposure can cause mild headaches or fatigue in sensitive people
• 50 – 100ppm: Maximum safe working levels for short periods. Can cause headaches and nausea after a few hours
• 200ppm: Severe headaches, dizziness and fatigue after 1 – 3 hours exposure
• 400ppm: Frontal headaches after 1 -2 hours exposure. Can be fatal after 2 – 3 hours exposure

The Health and Safety Executive (HSE) recommends a maximum of 20ppm over a prolonged period but some organisations only recommend a maximum of 35ppm Time Weighted Average (TWA) over an eight-hour period.

How should alarms react to increased levels?

The main problem I can see with levels and alarms is that British Standards (BS 50291) does not require a CO alarm to sound until the levels are over 50ppm for prolonged periods, usually between 60 and 90 minutes of continuous exposure. If the levels drop during this period the time starts again.

Alarms made to this standard therefore operate as follows:

• 50ppm – alarm sounds between 60 to 90 minutes of continuous exposure
• 100ppm – alarm sounds between 10 to 40 minutes of continuous exposure
• 300ppm – alarm sounds after three minutes of continuous exposure

So, while I was clearly reading, and reacting to raised levels of CO, the level of 47ppm measured in the living room would never trigger the alarm. And, on checking the alarms – one was in the living room and another one near the gas boiler – both were installed in the correct position, working and well within date. And yet my physical reaction and the readings meant there clearly was an issue.

A bit of detective work ensued and I was able to establish that the problem was originating from the boiler. When I measured the boiler room the level was 69ppm but this was dropping. However, when I turned the boiler on, the level rose to 117ppm.

The boiler was a combi-boiler so only ran while water was being drawn off, and the people who lived in the home would only really run hot water for around 5 – 10 minutes each time. This meant the alarm would likely not sound until levels got to over 300ppm as the exposure was not continuous.

When the boiler was turned off the levels would drop again due to natural adventitious ventilation in the home, but only to around 47ppm, meaning that the occupants of the home were being continuously exposed to low levels of CO poisoning.

On inspection I found a small leak in the boiler flue, which was easily remedied, but this story could have had a very different outcome. Although the CO alarms were new, functional and doing exactly what they are designed to do, I believe it is not enough.

On my recommendation the homeowners have now changed the alarms to ones with a digital readout that, although won’t sound the alarm if a similar situation occurs, will show the real time CO levels on the display that they can monitor. I actually keep one with me when I stay in hotels, and especially when on holiday in a holiday park or caravan.

Air quality monitors, such as this Aranet4 HOME Monitor tested by one of the Homebuilding & Renovating team can also be a good addition to a standard CO alarm, providing you with constant real-time air quality readings in your home, including CO levels.

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Do other alarms have similar flaws?

CO alarms are not the only alarms in the home where some extra vigilance won't go amiss. Most homes have smoke or fire alarms, yet it surprises me how many people have removed the battery from their alarms due to nuisance alarms or the intermittent beep noises when the battery is low.

These noises are not a problem with the alarm – they are a user issue.

There are three main types of smoke alarm. Older smoke alarms were known as ionization alarms, these were very sensitive to steam and cooking smells, leading to them going off more frequently than you needed them to, hence why many people would simply remove the battery.

If you still have these in your home, it is best to understand how to properly fireproof your home and replace them with optical (photoelectric) alarms. These have a light beam shining into a sensor. Smoke scatters the light which then triggers the alarm.

They are very good at detecting very slow, smouldering burns from soft furnishings or overheated wires, and should ideally be used in bedrooms and living areas where there is a possibility of this type of fire.

However, they should not be placed in a kitchen as they do not go off if there is a very hot fire. In kitchens you need a heat alarm which has a thermal sensor that triggers when the room reaches a specific temperature (usually around 58˚C) – but it won't detect smoke, so you can rest assured the odd bit of burnt toast won't set it off.

Another good location for heat alarms is in garages as it will help avoid nuisance triggers from exhaust fumes.

The third type, multi-sensor (combination) alarms have a heat sensor and an optical smoke sensor. These are best for hallways, escape routes and general living areas where a heat fire, or a smouldering fire could happen, but not in an area where nuisance triggering is likely.

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How you can avoid similar problems

As with many technical appliances, it is best to stick with reputable brands, make sure that the battery backup is routinely tested and that the alarm is fit for purpose. After all, it is there for one purpose only and you want to be sure that it does its job if required.

Tethering (linking) alarms is also an additional safety feature to consider. This means the alarms are all designed to be linked together either via wires, or wirelessly in an existing home where installing wires would be very disruptive. These alarms will all sound if one of them triggers, so if you are asleep in a bedroom at the opposite end of the home and the heat alarm in the kitchen activates, then the smoke alarm in the bedroom will also sound to make sure that you can hear it and wake up.

Some products can also be linked to smart home controls, or your phone, to alert a third party if the alarm is triggered. This is particularly useful if an elderly person or someone hard of hearing lives on their own, perhaps in an annexe, and they may not hear the alarm. Someone in the main home, family member, friend, or a security company, can then go and check on them.

Safety alarms are there for a reason and we need to be sure that they are fitted correctly, are fully functional and keep you safe. Not all homes are the same and not all alarms are the same. Do your homework and get the best system for you and your family. This is not one of those areas where you should be penny-pinching.

If you're embarking on a self-build and need to make sure your home will be equipped with the right alarms, our guide to Part B: Fire Safety Regulations of the Building Regulations will help you understand what's required. And, for advice on the air inside your home in general, find out how to improve the air quality so that you can be confident it's as clean as it can be.