Carbon Monoxide alarm - genuine or not?
A few months back I put my boat ashore into its cradle for the winter, and plugged the mains cable into the nearby supply. On my B36 with the mains breaker onboard switched to on, the domestic and engine batteries began recharging, and all was well with the world.
I intended to stay onboard that night, and in due course turned in. The only circuits energised at the time were those for the cabin lighting, the domestic water pump and the battery charger which was still working. But at around one in the morning a Carbon Monoxide detector I'd installed a couple of years earlier, went into alarm. After opening all the hatches and waiting for a while in the open air of the cockpit, the alarm reading which had registered around 70ppm dropped to 10 or 15, and the alarm noise had stopped. While outside I'd been trying to think what could possibly have caused the production of carbon monoxide, and had drawn a blank. There were no heating appliances running, despite the cold, and the gas oven and hob were all off and the gas isolating valve was shut. There were no evident problems with lighting circuits or from the water pump, and that only left the batteries which continued to be trickle charged. The batteries consisted of two 140ah domestic and one 100ah engine start battery. All batteries were of the lead acid variety, and of which the domestics were known to be getting rather old and which tended to loose their charge quite quickly. As a result charging during the day had not reached the point where the charger might have gone into floating mode.
During charging, it is known that lead acid batteries do give off some hydrogen gas, and the older and less reliable the battery becomes, the more gas it tends to give off.
Once back home I did an Internet search and found several references to CO detectors going into alarm when in the vicinity of lead acid batteries in process of being charged, including an excerpt from an article where the writer had learned of the following substances, all of which would have an effect on the readings shown on a CO detector, and note the third and the penultimate entries:-
Aerosols ? (hair sprays, deodorizers, Lysol, etc?)
Cleaning supplies ? (Clorox, Bleaches, etc?)
Gas from charging batteries
Paints
Stripping chemicals
Varnish
Silicon glue or compounds
Alcohol
Methane
Toluene
Acetone
Nail polish
Nail polish remover
Sulfur compounds
Sewer gas
Vapors from baby diapers
Car exhaust fumes
Cigarette smoke
Incense smoke
Ammonia
Carpet cleaning solutions
Sealant
Freon from air conditioners
Hydrogen
Nitroglycerin (usually from heart medication)
The guy writing the article had hesitated to publish the list above since some of the items do contain CO and he did not want to give the impression that there are so many substances that interfere with a CO detector that it might be better not to have one.
His other concern, and mine, was whether the hydrogen level was high enough to create an explosive or flammable environment. He went on to say that he was relieved to read of a case where the fire department ?Using a cross-sensitivity table supplied by one of the CO sensor manufacturers, showed that 80 ppm on the CO sensor meant that there was approximately 200 ppm of hydrogen present. This is well below hydrogen Lower Explosive Limit (LEL) of 4 percent (40,000ppm)? Note my CO monitor was reading 70ppm by the time that I got to looking at it, or 140ppm of hydrogen, and this would have been hugely below the point at which the boats LPG gas detector would have picked up the presence of flammable gas.
Hydrogen gas is not poisonous, and should not be detrimental to health other than that it might in sufficient quantity result in suffocation, or in sufficient quantity reach the flammable level.
A few days later, and again while staying onboard overnight with the mains cable plugged in and the batteries being charged, the same thing happened again.
Initially the obvious thing to do was not to leave the batteries on charge overnight if I wanted to get any sleep, but a problem onboard my B36 (2002) was that there was no isolating switch for the "Quick" battery charger that would allow it to be turned off. Instead, it was hard wired direct to the incoming mains, and that meant the mains would have to be shut off, or the batteries would continue to charge and emit hydrogen gas that would in turn trigger the CO alarm.
Since then I've installed an illuminated switch similar to the one used for the calorifier, and which now permits the battery charger to be switched on or off independently of the rest of the 220volt circuits, and I've also replaced the old domestic batteries for new ones which charge and allow the battery charger to go into float mode.
The moral of the story being that if a carbon monoxide alarm goes off, get yourself and others out into fresh air as fast as you can, but be aware that it may not actually be carbon monoxide that triggered the alarm.
As always, never underestimate the danger that carbon monoxide represents, but when it's safe, to do your best to try to determine the cause of the alarm, keeping in mind that there are a number of other substances, the presence of which can also be detected by a CO detector, causing it to register an apparently dangerous condition.
