Spurious Gas Alarms

[aardvarkinvader]

Ok chaps, a biff at the keyboard with a problem. My yacht is a Southerly 115 and having witnessed HMSTC Lord Trenchard blow up in Poole a few years ago am a little paranoid about gas various. I have a gas alarm fitted and carbon monoxide and smoke detectors in the sleeping cabins. Gas locker is sealed and drains overboard.
After a pleasant sail and about 15 minutes under motor, I moored at Poole Quay, and set to some maintanance. About an hour later the gas alarm sounded, a quick look on deck revealed the wife, who had not sprayed any expensive muck on herself, so I checked very thoroughly over the boat. Gas was still off at the bottle (has not been on for a couple of months), bilges dry and no smell of gas anywhere. Left hatches open, pumped bilges and did all the good stuff. About an hour later it repeated, as did I, again nothing found. This went on for a few hours before I disabled it.
Head down after supper, fast asleep untill the CO alarm in the aft cabin went off at 0400. Checked all over the boat, could find nothing hot or smouldering, it is now hours since the engine has run and we have not cooked anything. Gas is still shut off tight and there are no funny smells. Like the gas alarm earlier, it repeated several times. We slept the rest of the night with all hatches open and ear plugs.
A very thorough look over everything the following morning revealed nothing out of the ordinary except 2 cells in one of the service batteries needed topping up.
In the 3 years we have owned her, nothing like this has happened before, what on earth could have set both the gas and the CO alarm of repeatedly on the same day? Help

 

[saltylegs]

any chance that the batteries were "gassing" while charging, this would also result in low fluid levels in the batteries?

 

[makingplansfor]

Last season I had the gas alarm go off - checked the gas system confirming all was ok. Looked close to the sensor and found liquid in the bilge - this was found to be a pretty good Chablis which had drained into the bilge from the cool box after the bottle had broken. Although it seemed unlikely that wine would trigger the alarm, it only cleared after the clear up!! Doesn't however go anywhere close to explaining the CO alarm.

Given that it was both alarms, could it be that large transients on the power supply could have triggered them e.g. frrom pumps or other electric motors running, suggesting that suppressors may have failed (a little knowledge being dangerous here - not even sure whether boat electrics have such suppressors - if I have them, don't know where they are!!)

 

[prv]

Can't provide a neat solution, just observing that the gas alarm went off on the boat that nearly sank under us. There was quite a lot of oil in the water from the engine bilge; we weren't sure if it was this or just the water itself that set off the alarm.

Could the sensor have got wet or oily?

Pete

 

[aardvarkinvader]

Thanks chaps, some interesting ideas, in particular a nice drop of chablis. The two sensors are low in the bilges but both bilge and sensors are (and were) clean and dry. Batteries gassing is an interesting possibility, is it Hydrogen which is given off from Lead Acid? And does anyone know if that will set off both gas and CO alarms?
Thanks again

 

[VicS]

Any flammable vapour will set off the gas alarm I think you will find.

I dont know how the CO sensors work

 

[greenalien]

The gas alarm will only react to hydrocarbons - butane and petrol fumes, for example - but not, as far as I know, to hydrogen - which is, in any case, being lighter than air, pretty unlikely to accumulate in the bilges.

CO detectors are specific to CO. They have a limited life, depends on the model but it's only something like 3 years, after which they need replacing. Not sure what the point is of having the detector in the bilge for this, as it's the breathable air that needs sampling for CO content, so I'd expect the detector to be in the saloon. I suppose it could be to detect an exhaust leak, depends on where the exhaust pipe is routed.

 

[VicS]

The gas alarm will only react to hydrocarbons - butane and petrol fumes, for example - but not, as far as I know, to hydrogen - which is, in any case, being lighter than air, pretty unlikely to accumulate in the bilges.

The old type of sensors did. We used to use one for finding hydrogen leaks.

 

[aardvarkinvader]

The gas alarm sensors are in the bilges, but the CO detectors are mid height in the 3 sleeping cabins. The one in the aft cabin sits above the bunk under which the exhaust pipe runs, but it had been about 10 hours since the engine had run though. They are just over 2 years old so I think I will change them just in case.
Thanks again.

 

[greenalien]

The other things that could set a CO alarm off are using a gas cooker with inadequate ventilation, or a faulty gas water heater.

 

[StugeronSteve]

Two possibilities:-

We have a gas sensor under the cooker and have had alarms after wiping round with cleaning agents (bleach type wet wipers), so could a bottle of something have leaked, or vented into the bilge?

Second possibility is, as has been mentioned, battery gas. We had a couple of calls from the marina to say that our gas alarm had been sounding and yet when they investigated they had found the gas isolated and no worrying smells. A few weeks later I found that our batteries had boiled dry. New batteries, no subsequent probs!

 

[beebok]

we had this problem a couple of years ago it was the batteries overcharging because one of the batteries was faulty.highly inflamable gas so take care.

 

[saltylegs]

CO detectors are specific to CO. They have a limited life, depends on the model but it's only something like 3 years, after which they need replacing. Not sure what the point is of having the detector in the bilge for this, as it's the breathable air that needs sampling for CO content, so I'd expect the detector to be in the saloon. I suppose it could be to detect an exhaust leak, depends on where the exhaust pipe is routed.[/QUOTE]

They are designed to be CO specific but most flamable gasses, aerosols and even thinners will set them off, you will find this described in the small print usually in the fault finding section of the instructions.

A good CO detector has a 5 year life and at the end of 5 years will make such an annoying constant chirp that you have to throw it away and get a new one.

 

[Stoaty]

I dont know how the CO sensors work

I was relying on Vic for an explanation about this.

All I know about the CO alarms is they have a radioactive element to them that lasts about 7 years.

Now when my battery charger decides it need to go into equalising mode. That means a long charge at high voltage (32V), lots of fizzing and me having to top up the batteries at the end of it. It sets of the CO alarm.

Now it's been 40 years since my chemistry A level but I am almost certain that CO is not given off by the batteries when charging, so something else must be going on. The wife reckons she can smell a faint odour of hot plastic when the batteries go into equalising mode and they are quite warm to touch in this mode. So I am leaning towards something leaching out of the battery casings, especially as my neighbour's CO alarm goes off when he forgets to take his batteries off charge for a week. That's on the weeks when he hasn't run them completely flat. He has different batteries, different charger and different CO alarm. In my mind there has to be a link between battery charging and CO alarms going off.

 

[VicS]

I was relying on Vic for an explanation about this.

All I know about the CO alarms is they have a radioactive element to them that lasts about 7 years.

Now when my battery charger decides it need to go into equalising mode. That means a long charge at high voltage (32V), lots of fizzing and me having to top up the batteries at the end of it. It sets of the CO alarm.

Now it's been 40 years since my chemistry A level but I am almost certain that CO is not given off by the batteries when charging, so something else must be going on. The wife reckons she can smell a faint odour of hot plastic when the batteries go into equalising mode and they are quite warm to touch in this mode. So I am leaning towards something leaching out of the battery casings, especially as my neighbour's CO alarm goes off when he forgets to take his batteries off charge for a week. That's on the weeks when he hasn't run them completely flat. He has different batteries, different charger and different CO alarm. In my mind there has to be a link between battery charging and CO alarms going off.

I have come across nothing to suggest carbon monoxide alarms contain a radioactive isotope. But cannot find much info on how they do work.

One of the types of smoke detectors OTOH contains a small amount of americium 241 which is an alpha emitter with a half life of over 400 years.

Unlikely I would have thought that carbon monoxide would be given off by a battery unless the case was almost on fire.

 

[nigelmercier]

The two sensors are low in the bilges...

The manufacturers of both gas alarms I have owned (Plastimo and Pilot) both stated categorically that the sensors must NOT be placed in a damp or wet area. When I queried this, they both advised NOT to fit them in the bilge.

 

[Stoaty]

This is how they work but no reference to any isotopes so I must be confused somewhere. Think mine is a metal-oxide type.

 

[VicS]

This is how they work but no reference to any isotopes so I must be confused somewhere. Think mine is a metal-oxide type.

Thanks I'd not found that page. Thats the best explanation i've seen.

I wonder how specific the metal oxide types are. Will they also respond to hydrogen. After all that too will reduce metal oxides to the metal!

 

[thalassa]

The clue is possibly in the text:
'.......converting itself into carbon dioxide, turning the metal oxide into pure metal, and producing heat at the same time. An electronic circuit monitors the temperature inside the chamber and sounds the alarm if too much heat is produced too quickly.'

I once had a call from the owner of the boat next to ours on the pontoon. He said he 'went mad from the alarms from your boat'. So I went to check. It was a hot summer and the temperature inside the cabin had risen to 33 degrees. In the end, I reluctantly had to disable the CO-alarm as well as the smoke alarm.
Mmm... not likely at this moment in 'summer'...
Will

 

[VicS]

The clue is possibly in the text:
'.......converting itself into carbon dioxide, turning the metal oxide into pure metal, and producing heat at the same time. An electronic circuit monitors the temperature inside the chamber and sounds the alarm if too much heat is produced too quickly.'

I once had a call from the owner of the boat next to ours on the pontoon. He said he 'went mad from the alarms from your boat'. So I went to check. It was a hot summer and the temperature inside the cabin had risen to 33 degrees. In the end, I reluctantly had to disable the CO-alarm as well as the smoke alarm.
Mmm... not likely at this moment in 'summer'...
Will

Being very sensitive to temperature you'd expect some form of reference measurement so that allowance was made for changes in ambient temperature.