Gas safety - am I fooling myself

[tillergirl]

First of all, I know other things are preferable to gas and it should really be sitting on the aft deck... However, I have two gas bottles sitting in the port cockpit locker. So a number of years ago, I made a watertight locker, which I hope is also gas tight and connected a drain (with seacock) venting portside. Now the fall from bottom of locker to skin fitting is not much and the pipework (owing to poor design - me) is not the fairest of runs. Hence I worry about how much split gas would actually vent. I know the locker is watertight because if I sail with the seacock open, it fills up with water so I have a regime of seacock on and off before and after sailing. But to help any split gas to escape, I have added a watertight plug to the lid of the locker which fits the inflater for the dinghy. So now everyso often, I plan to remove the plug, and pump fresh air into the locker thereby forcing any gas through the vent at the bottom (always remembering to open the seacock first!).

Am I deluding myself? Am I just swirling any gas that might be there around?

 

[kds]

Why don't you get your man to suck on the outboard end of the pipe - so long as he doesn't smoke !
Ken

 

[boatone]

Two things here....1. Keeping all the connections gas tight so there are no leaks and...2. Making sure that any gas that does leak can escape safely and not build up a dangerous concentration.
You seem to be concentrating more on 2 than on 1 ! If everything is gastight there will be minimum risk of a build up but.......
The gas is heavier than air so will lie in the bottom of the locker unless it can escape through a skin fitting. This must be lower than the bottom of the locker (only just though...doesnt have to be much lower)but if the outlet is below the waterline the water will effectively block the escape of the gas.
Have you thought of installing a gas alarm in the locker which will alert you to a build up? Alternatively, your idea of forcing air thru the locker seems a good one as long as you overcome the backpressure of any water in the outlet pipe.
As a matter of interest, do you have a gas alarm in the cabin/worry about leaks from the appliances etc?

 

[Sixpence]

you don't say if you have a gas detector fitted ( no I don't mean your nose ) I have been on the recieving end of a catastrophic gas leak and subsequent fire so I am more cautios than most .
Dave

 

[Plum]

You have already had some good advice, but may I just add that the airtight hose/pipe from the bottom of the gas locker to overboard should be at least 1/2 inch bore and be down-hill all the way to ensure no water traps which will effectively block or restrict the pipe. If this is not the case, then your idea of pumping air into the top of the locker may, if the top of the locker is not completely gas-tight, actually force any gas out the top of the locker and into the boat.

Hope this helps.

 

[tillergirl]

Oh dear, I should have delivered a full spec to save you all some time. Yes, all the connections are gas tight and tested. Yes, I have a minimum of 1/2" bore and its at the bottom of the locker and the skin fitting is above the waterline. Defects - the fall from bottom of locker to skin fittings is pretty slight (but there wasn't any other way to do it). The lid is designed to be air tight but I confess I didn't get it pressure tested.

I haven't got an alarm because the last one used to go off when there wasn't a leak and didn't go off when there was one!

I think the point about water in the pipe is a good one and pretty difficult to assess without poking something down the pipe, which means opening the lid which means that the contents might overspill - bit tricky that! Perhaps I do need a man to swim alongside and occasionally suck on the skin fitting!!!!

Thanks all

 

[boatone]

I think you are worrying unduly. If the skin fitting outlet is above the waterline and even marginally below the bottom of the locker any gas in the locker will drain. Ok, if you heel over and water enters the pipe it will temporarily block escape but hey, u surely arent saying theres a continuous leak are you????

 

[tillergirl]

No I'm not saying there's a continuous leak. But if the box is watertight and therefore gastight and the lid is tight, will the gas actuall fall out?

 

[boatone]

I'd be surprised if the lid is airtight so yes, i would expect any gas to drain away. One way to test....put some water in the locker and see if it drains away when you replace the lid.

 

[MacW]

Latest regs actually call for the lid to be vented. If the locker is sealed up tight, except for the drain, then you are correct - the gas can`t drain out cos it would leave a vacuum.LPG is very much a `searching` gas and will find its way out of the drain no problem.
cheers
Pete

 

[tillergirl]

Thank you for that

 

[MacW]

Further to last post, no point in sealing lid anyway, as it would have to be opened frequently to turn on or off the gas AT THE CYLINDER everytime you use the cooker, heater or water heater, unless you have a remotely operated solenoid gas valve in the cylinder locker.

 

[tillergirl]

Yes I know and it isn't sealed.

 

[Talbot]

If you had vented through the stern, you would have had less trouble with the heeling.

 

[tillergirl]

Not possible. No room behind the transom, poor access to the rear transom area and the skin fitting would go under water under power. Where it is, is the best compromise that reduces pipe runs and has the highest freeboard. The theory is that if I have a gas leak underway - I hope with all the other precautions, only a minor leak, then the gas will be contained in the locker until I open up the seacock when at the destination.

 

[Peterduck]

I'm probably an old Luddite, but I'd be a bit distrustful of an electric solenoid gas valve. I'd much sooner have a manually operated valve somewhere [inside, in case it's raining cats and dogs!]. at least then if it sticks or fails to close for some reason, I know about it.
Peter.

 

[boatone]

I still think you are going way OTT with this.
Provided the path from the hole in the base of the locker to the overside outlet is marginally downwards and the locker is not absolutely airtight then any gas accumulaing in the base of the locker WILL drain away whenever the outlet is 'free to air'..ie not blocked by water due to adverse heeling.
You seem to be worrying about a catastrophic leak of gas and you can avoid that by shutting off the gas AT THE BOTTLE when underway and only turning it on when in port.

 

[tillergirl]

How do you cook while underway or make hot drinks? I was worried about the accumulation of small escapes but you've satisfied me on that point.

 

[boatone]

If you have a well installed system then I dont think you need to worry about this as much as you seeem to. Have you ever had your gas sytem checked by a competent corgi installer? They will test for leaks and ensure the system is gas tight at all unions.
You could even have a primary gas stopcock installed just inside the cabin so that you can easily isolate the appliances with a single valve and leave the bottle valve open. Alternatively just lift the lid and turn it on and off in the locker when you need it.

(I am on the inland waterways where the Boat Safety Scheme requires the gas system to be pressure tested for leaks. Its quite unnnerving to sit there watching a mercury anemometer to see if the instrument shows pressure loss !)

 

[Talbot]

sounds like a recipe for disaster to me. There is no way that your locker could contain a gas leak - sooner you than me, and would prefer you not to raft up to me!

Notwithstanding this, it is still better than some peoples concept of gas safety