On two consecutive mornings this week, the carbon monoxide gas alarm was sounding when I got to Hali. On the first morning, the propane gas detector was also sounding. In each case, the boat had not been used, and the engine had not been run, since the night before. The boat was relatively buttoned up, with only the vent hatches in the head and the aft cabin having been left open. The CO monitor read-out was in the 80-90 ppm range but subsided to zero within about five minutes after the hatches and port lights were opened. There was no noticeable smell (such as of propane or sewer gas) in the boat.
On the third and fourth mornings, in similar conditions except apparently one, no alarm was sounding. The exception is that the night before the third day, a co-owner checked the propane tank valve and found she could tighten it somewhat more firmly.
Recent work on the boat had included replacing the two 4D house batteries (the new batteries have removable cell caps whereas the old ones apparently didn't) and putting a marine "no odour" product into the shower sump drain and toilet-waste line-holding tank.
The carbon monoxide gas detector is surface mounted on the starboard side of the engine box in the aft cabin about a foot from the floor. It is a Kidde (3 AA battery operated) Carbon Monoxide Alarm with digital display and peak level memory Model KN-COPP-BCA Assembly 900-0146 manufactured on October 23, 2006. It has a five year warranty. Its User’s Guide says it was “not designed to detect smoke, fire or any other gases.” It is an electrochemical device. A note in the User’s Guide says, “The following substances an affect the sensor and may cause false readings: Methane, propane, iso-butane, ethylene, benzene, toluene, ethyl acetate, hydrogen sulphide, sulfur dioxides, alcohol based products, paint thinners, solvents, adhesives, hair sprays, after shaves, and some cleaning agents.” The unit had been powered up in March or April, 2007, and not re-powered or "peak display" tested since then. When the “Peak Level Display” button was pressed and held (which results in the display showing the highest CO reading recorded since the last peak level test or power-up) the reading given was 159. This was after the second morning.
I read at the Centres for Disease Control website that the "Occupational Safety and Health Administration (OSHA) has two permissible exposure limits (PELs) for CO exposure. Exposures may not be over 35 ppm averaged over 8 hours and may never be over 200 ppm."
The propane gas monitor on Hali is surface mounted within 6" of the cabin sole at the base of the galley isthmus and is a hardwired 12 volt model GS/3 manufactured by Electro Systems Inc. in June, 2002. I haven't checked yet whether it is out of warranty. It was sounding an alarm (occasional beeping) that does not appear to be consistent with the presence of propane (but whether it would be consistent with the presence of some other gas hasn't been ascertained yet).
Nonetheless, a check on the propane gas line is in order...but hasn't been done yet.
Hali is docked in a marina. A powerboat across the finger from Hali was gone on the first morning that the alarms were sounding...and possibly had left shortly beforehand but that is not know yet. No nearby boat seems to have departed or been run on the second morning.
I understand that while carbon monoxide is generally only associated with incomplete combustion, it is at least theoretically possible for carbon monoxide to be produced when hydrogen sulphide (sewer gas) comes into contact with hypochlorite, an ingredient of bleach.
http://web.bsu.edu/IEN/archives/111607.htmMy current theories are:
- there was a propane leak
- there was carbon monoxide, probably produced from a nearby boat but possibly built up the evening before when Hali was run but which caused the CO alarm to sound only after its time sampling was sufficient (after we left) and which continued until the next morning
- the most unlikely theory is that the CO was produced in Hali's drain or waste line
- the new batteries are throwing off a gas that is tripping the alarms
- more than one of the above (and therefore a gumption trap)
Comments and suggestions would be appreciated.
See a fascinating posting by sailingdolphin about CO poisoning at
http://c34.org/bbs/index.php/topic,2874.msg15204.html#msg15204.