Gas alarm - CO detector or not what'ya reckon?

[AntarcticPilot]

I can also smell butane or propane, but that doesn’t mean that I will always smell a gas leak. That’s because, being heavier than air, it will sink to the bilges where it will be below the level of my nose.

The stink that is put in gas is detectable by a normal sense of smell at gas concentrations far below an explosive mixture. I've never encountered it, but I understand that explosive gas concentrations smell badly enough to cause nausea; always provided that the person concerned has a normal sense of smell. Think how you can easily smell the tiny amount of gas released when you are a bit slow lighting the cooker! In my bilges, which are very shallow (less than a foot below the cabin sole at the deepest point), a concentration of gas even at a low level would result in an easily detectable smell, as diffusion would ensure that the smell spread (think how you can easily smell even a small amount of diesel in the bilges - and that is much heavier and far less smelly than odorized Butane or Propane).

The problem you note would exist in deep bilges closed off from the rest of the cabin; of course in such a situation, a gas detector would be a sensible precaution, as it is for those persons whose sense of smell does not operate for the stink in gas fuel. I fully understand that situation; I happen to be unable to detect ammonia until it is strong enough to make me cough!

 

[lw395]

I can also smell butane or propane, but that doesn’t mean that I will always smell a gas leak. That’s because, being heavier than air, it will sink to the bilges where it will be below the level of my nose.

That's not entirely true.
Gas is a gas not a liquid. Gases mix, the air is 20% oxygen at both floor and ceiling level.

A CO detector is a good idea on any vessel with more than just a basic gas cooker.
I would get a cheap one of good brand, e.g. Kidde and replace it frequently as they are hard to test.
Gas detectors can be tested using a squirt from a lighter.
Remember the Lord Trenchard had gas detectors!

The moist atmosphere inside a yacht is not good for things like sensors and unsealed electronics. Gas detectors mounted in the bilge are especially doomed. I would only have faith in something either new or tested, preferably both.

 

[Angele]

That's not entirely true.
Gas is a gas not a liquid. Gases mix, the air is 20% oxygen at both floor and ceiling level.

Gases do mix, and so do many (but not all) liquids. But, if the air is static (such as in the locker below my oven, where the gas tap is located) then heavier gases (butane) will tend to concentrate at the bottom and lighter gases (nitrogen and oxygen) will tend to rise. From the bottom of that locker, which is open at the rear, it is entirely possible for those heavier gases to sink down into my bilges.

Oxygen is only slightly heavier than nitrogen - hence why the concentration is relatively constant at different heights. Butane is twice the mass.

A CO detector is a good idea on any vessel with more than just a basic gas cooker.
I would get a cheap one of good brand, e.g. Kidde and replace it frequently as they are hard to test.

Agreed, I bought one at Argos on Saturday - the type with a digital display - now all I need is to find a dodgy setup so that I can test it!

The instructions say that it is designed to self destruct after 7 years, although it has a printed label that says manufactured in August 2010 and expiry August 2018. So, I've been slightly shortchanged in not getting the full seven years. But, at around £5 per annum, I'm not going to quibble.

The moist atmosphere inside a yacht is not good for things like sensors and unsealed electronics. Gas detectors mounted in the bilge are especially doomed. I would only have faith in something either new or tested, preferably both.

Agreed. My current gas sensor is only 7 years old and it is not working. I have no idea how long it is has been non-functioning. And, to my knowledge it has never got wet. I understand that is almost guaranteed to finish one off.