carbon monoxide alarms

[Peter Taylor]

The RYA has just sent out a "Be Alarmed" email about fitting CO alarms so I thought I would share my recent experiences in fitting an alarm in my BC20. I am using a single burner Origo spirit stove burning bio-ethanol mounted in gimbals in a home made wooden unit. It can be moved into the cockpit for cooking but for making an early morning cup of tea the unit gets used slotted into holders at the side of my sink (see photo). I therefore installed a "Firehawk CO78" CO alarm in the cabin.

In a small boat it is impossible to mount a CO alarm the stipulated distance from the potential CO source,  "doors and draughts", "ceilings", sinks, etc. etc. Perhaps for that reason, as soon as I lit the stove the alarm always went off. I was fairly sure I was not dying so in the end the alarm got permanently switched off - which rather defeated the objective!

After a conversation from a neighbour who lives aboard his boat I bought a First Alert CO410 alarm (photo). This has a digital display of CO concentration and integrates your exposure level before sounding its alarm. Boiling a single cupful of water in the closed (but ventilated) cabin gradually raises the CO level to a peak of 100 - 120ppm. This is not enough to trigger the alarm which is specified to sound after 10 to 40 minutes exposure to 100ppm. As a guide, the alarm instructions say that 100ppm for 20 minutes should not affect average, healthy adults but may cause headaches after 4 hours. Experimenting with larger amounts of water in the kettle showed that, with my arrangement of stove and ventilation,  the alarm actually triggers at around 20 minutes by which time the CO level is around 140ppm. For comparison, exposure to 400ppm can cause headaches after 35 minutes and kill in 2 hours.

My conclusions:
(1) I was actually surprised that the stove was producing detectable CO since the bio-ethanol burns with a blue, almost invisible flame and does not soot up the bottom of the kettle. It was not obviously deprived of oxygen. I may try watering down the fuel which is supposed to help although I'm not sure why. Boiling a cup of tea within the cabin is OK but cooking should definitely be done outside.

(2) Clearly some sort of CO alarm is vital. However an on/off type of alarm proved too sensitive to be useful in the confines of a small boat. I would definitely recommend installing an alarm with a digital display (I didn't shop around but paid just under £30 in Wickes).

Peter

[Tony]

Hi, Peter.
Only just come across your post.
Couldn't agree more about using stoves in a small cabin. To make sure that CO does not build up to an unfortunate level the ventilation must be so thorough that you might as well cook in the cockpit in the first place!
Any naked flame is going to generate a percentage of CO along with the CO2 whichever hydrocarbon you use and however efficient the burner is claimed to be. To add to the unpleasantness of stoves in confined spaces is the amount of water released during combustion. This condenses on any cold surface it finds (eg cabin sides, bilges, my bald head) making life miserable. (Getting a faceful of spray is one thing, finding an unexpected puddle forming under my sleeping bag is quite another!)
By the way, if you need to warm the air in your cabin on a chilly evening try a couple of good, oldfashioned hot water bottles strategically placed (and another in the sleeping bag er.. if you have nothing better available. )

[Peter Taylor]

Hi Tony,

I think my BC20 cabin might be a bit big for warming with a hot water bottle. I did mention the cabin heater I plan to use in the BC20 in a different thread. It is designed to exhaust the stove gases to the outside. It worked well in my shed but has had a mixed performance in a couple of trials in the boat and may need a fan installed in the outlet pipe. Given the warm winter I haven't pursued the problem but I'll report back when I do.

The main purpose of my post was to recommend the digital CO alarm over other types. I must admit I like to be able to brew a cup of tea within the cabin in a morning so a CO alarm is needed - but yes it will certainly increase condensation! I try to minimise the latter effect by starting with a flask of hot water prepared previously so it only needs to be briefly reheated within the cabin. When sailing, hot water from a flask reheated in the cockpit using an electric one-cup immersion heater is a viable method - as long as the water is reasonably hot to start with... heating water from cold using 12v is not a good idea!

Peter