gas alarm problems

[mldpt]

Hi I am having problems on board. If I run my mains charger for extended amount of time (12 hours) and the boat is closed up, there is ventilation in the roof, my gas alarm goes off, as this is located in the lowest part of the bilge how is the Hydrogen vented from the batteries getting down there, has anybody had this problem. I have changed my alarm twice now the last one was withdrawn by the makers SF distribution and replaced free of charge by an Amos L/P/G gas alarm has any body had this problem.
Regards Mike

 

[Eeyore]

A friend in the marina here has a similar problem. If the shore power goes off for any reason, then comes back on......his batteries tend to 'over-gas' and the gas alarm goes off. It's a bit of a pain when thunderstorms cut the power several times during the night! I don't know the solution, but I'll draw his attention to your post and see what results you get.

 

[pyrojames]

From memory most gas detectors do not detect hydrogen. The technology ofr H2 detection is different to CH. I'd doubt very much whether your alarm is going off because of hydrogen. Maybe HCl or H2S? I am not familiar enough with the IR bands for these to know whether there is a likely overlap with the CH lines.

 

[VicS]

Interesting slant you have put on things by suggesting that simple gas detectors are based on Infra red spectra. Gas concentration measuring instruments for specific gases may be (some are UV as well I think) but aren't these simple ones flammable gas monitors just thermal detectors that respond to any flammable gas. Some good few years since I have done any of this sort of work i must admit but in the days when I was using flammable gas meters they where based on a hot wire, although i realise thermistors replaced those.

I would not be entirely surprised by hydrogen from a gassing battery being detected by a monitor in the bilges. it may be light but it also diffuses very quickly and will soon become detectable throughout the space into which it is released.

 

[pvb]

Reckon you're right, Vic, that simple pellistor-based gas detectors will react to any flammable gas including hydrogen.

 

[Robin]

Ours went off on our last boat when a battery charger failed and the batteries were gassing, fortunately when we were on board and could sort it out promptly. The one on our current boat went off after I used Evostik contact adhesive to stick back a lining in a locker near the sensor, strong smell of solvent. We also met a couple on a large yacht with a gas sensor that automatically shut down the gas system which it regularly did, the cause was leaking Freon from the fridge so they had no ice or hot tea.

 

[pyrojames]

I stand corrected. /forums/images/graemlins/smile.gif

 

[NorthUp]

Hydrogen will not lie in your bilges, unless you first invert the boat...

 

[pyrojames]

But it has a very high diffusion rate, so if the batteries are in the bilge space, hydrogen at the sensor is not unlikely.

 

[VicS]

[ QUOTE ]
But it has a very high diffusion rate

[/ QUOTE ] As I had already said.

It is also demonstrated in school science lessons.

A gas jar is filled with hydrogen and inverted over another containing only air.

Later in the lesson the gas in both jars is tested, in the usual way for hydrogen, with a lighted splint. And what to we find? A similar explosive pop from each jar showing that the hydrogen has diffused from the upper jar in to the lower jar and as far as a simple experiment of that nature can show that the concentration is the same in both jars. Clearly a gas alarm in the bottom of the lower jar would have sounded within a very short time.

 

[Mariner69]

I was down in Hasler, Gosport and noted the gas alarm on one of the yachts was sounding. I mentioned it to the security guards who explained that the alarms are supposed to be switched off when the boats are left unmanned as the alarms react to the methane released at low water. It seems it is a common problem there.

 

[mldpt]

I know that Hydrogen is lighter than air therefore must be vented out of the boat but what other reason is there that could cause the alarm to go off when the mains charger is charging, and the boat is closed up, I can only imagine that the boat is full therefore it would get into the Bilge. I have just installed a solar powered ventilator so will see what effect that has. I am not sure if a LPG sensor will detect Hydrogen anyway, but there is deffinetly no LPG gas in the bilge.
Regards Mike

 

[Miker]

Interesting. I have virtually given up on my fixed gas alarm which goes off even if I have no gaz bottles aboard. And at times the hand-held one goes off even outside the boat in the marina. I had put it down to the nearby fish dock but I suppose that it could be methane.