Some context might be needed here: For the last 32 months I have been running a tugboat company. I intend to write more about that at some point.
We operate a fleet of four tugboats and associated barges, smaller boats, and other equipment. Our tugboats are equipped with, among other safety equipment, carbon monoxide (CO) detectors in interior spaces. Last week, two CO detectors started sounding. It was important that we determine the source of the carbon monoxide as it might harm crew. The obvious concern was that there was some leak in the exhaust system.
An aside for those who might not be familiar with the chemistry: Internal combustion engines that burn hydrocarbons such as gasoline or diesel consume oxygen (from the air) and hydrocarbons (fuel in the form of a hydrocarbon such as gasoline or diesel) and emit various waste gases and particulates, including carbon monoxide (CO), carbon dioxide (CO2), nitrogen monoxide (NO), nitrogen dioxide (NO2), sulfur dioxide (SO2), and unburned hydrocarbons. The most dangerous of these is carbon monoxide as it is poisonous, flammable, colorless, odorless, tasteless, and slightly less dense than air. This latter attribute can lead to it collecting in spaces. The biggest concern is that it might build up where crew are sleeping and kill or injure them (brain damage is one possible injury for those not killed by CO poisoning).
This particular tugboat has two main diesel engines for propulsion and two diesel generators, which power all other systems. At the time that the detectors started sounding alarm, the boat was idle at a dock, so only one generator was running.
Carbon monoxide in air is measured in parts per million (PPM). Normal air should contain no more than 5 PPM CO. 50 PPM and above is dangerous.
To test, we opened all of the doors and ran the generator while a crewman walked around inside the compartments with a handheld CO monitor. Our intent was to find where in the exhaust system we were leaking carbon monoxide. This inspection yielded confusing results at first. We found no emissions at the generator and 17 PPM in the wheelhouse. This was confusing because the exhaust system does not run through the wheelhouse. Inspection of other areas (bunk rooms, importantly) found no emissions.
The crewman kept poking around and found that the CO monitor was reading 62 PPM around a lead-acid battery in the wheelhouse under the helm. There is a larger bank of batteries down below that serves engines and generators. The battery in the wheelhouse is in a circuit used just for the 12V electronics (e.g., radar, VHF radio). It is kept charged by a 110V battery charger that is powered by the generators. Such configurations are common in boats like this. This allows one to use radios to call for help even if all engines are inoperable and under water.
But why would a battery be emitting CO? It does not. Lead-acid batteries can emit hydrogen (H, which immediately binds into H2) when failing or when the charger is overcharging. Some carbon monoxide detectors will register hydrogen as carbon monoxide (“Cross-sensitivity between carbon monoxide detectors and hydrogen gas is well documented and publicized.“) Our crewman found an article that explains similar findings by firemen (they found a golf cart battery charger in a garage emitting enough hydrogen to set off a carbon monoxide alarm).
This changes the concern. We do not appear to have a carbon monoxide leak at all. We appear to have a buildup of hydrogen. This is still dangerous as collecting hydrogen in an enclosed space could lead to an explosion or fire.
We are investigating and remediating the battery problem now, which should be trivial. Maybe the battery needs to be replaced, maybe the charger is broken. We might relocate the battery out of the wheelhouse.
The interesting lesson to me is that CO alarms might not mean CO at all.