Gasoline Vapor

[Gary Gover]

My greatest engine safety concern is for the possible accumulation of explosive vapor in the bilge. If I remember right, an ounce of gasoline properly mixed with air has the explosive power of a quarter pound of TNT.

The Atomic 4, being a marine engine, has features to manage the risk, such as are built into the carburetor and fuel pump, and I've taken some some additional measures. I've installed extra 'natural' ventilation for the bilge. I use an electronic gasoline vapor detector in the engine space. I run the bilge blower all the time the engine is running. I always run the bilge blower for five minutes before starting the engine and run it for ten minutes before starting after fueling. I close the boat up tight during fueling. I keep the bilge fairly dry to keep the vent ducting open and free of water.

Specially, because crankcase vapors contain unburned fuel and because the crankcase of the Atomic 4 is not sealed at the forward end of the crankshaft and because the engine's means of crankcase scavenging thru the carburetor flame arrester is so weak, I have ducted the crankcase vent pipe overboard and fitted that duct with an exhaust blower.

I annually carefully inspect using a checklist the fuel tank and all its lines and fittings to see that everything remains is good condition, tight and leak free. I have replaced any nylon fuel fittings with bronze fittings and any old flexible fuel lines with modern approved fire resistant lines.

An explosion onboard is my top engine safety concern, followed closely by similarly rooted risks of fire involving fuel or oil or risks of accumulation of engine vapors inboard.

[Don Moyer]

Gary,

A very professional approach. Thank you for sharing.

Don

[Mo]

But for the grace.....

Summer 2007 -

I was overhauling my boat when I first bought her...had built a trailer / cradle and had her in the driveway in front of my garage...walk in the park. Just finished the overhaul on painting, wiring etc etc etc. I was leaving the engine until last.

I had messed with the engine a bit and left the fuel shut-off open. Went in the house overnight and came out at 8am to go back at it. The sun was already beating on the deck.

It was only a miracle that I didn't have a cigarette in my mouth as I opened the hatch. The fumes hit me in the face. She had dumped at least five gallons of gas in the bilge..it ran through a malfunctioning carb that I had not even touched yet. I've been to a few of war zones but that was the closest I came to being blown up...the fumes were so strong that it just would have been a bang.

Carefully soaked it up with a car-wash sponge...squeeze by squeeze...into funnel and gas can. There are 2 fuel shut-offs on the boat. I ensure one is closed when I leave daily. I got that lesson without paying the price.

[Al Schober]

One of the first 'adds' to our A4 equipped boat was a fume sniffer. That was back in '88. Since then it's gone off twice, and neither time was related to the engine.
First was a gas jug for the dingy that had gotten onto its side in the lazarette. A slow drip was enough to trigger the sniffer.
Second time was while taking on fuel. Turned out to be a bad hose between the tank and the deck fill.
The first one makes me wonder about the folks that feel so safe because they have a diesel inboard - no need to worry about gas, right? Where do they store their gas jugs for their dingy? Or perhaps they have diesel outboards...

Al

[ArtJ]

We have to be careful with the gasoline fume detector mounting.
I had one become loose and fall into bilge water. It caused a alarm and
a expensive sensor replacement I think it was well over 100 bucks.

[Mo]

A bit of patience and avoid the Harp.

Hi Guys.

Not so common sense.

If you enter a boat and even have a hit of gas smell DO NOT TOUCH POWER SWITCHES....DO NOT TURN POWER ON...LEAVE OFF....open forward hatch, lazarettes, if your steps cover engine compartment remove them to let air flow through, lift out bilge flooring, and leave companionway open....Do not even touch the blower switch for 10 minutes .

If you don't have a detector, leave the boat area and come back 15 minutes later. Your nose gets accustomed to the gas smell and may deceive you. Leave for a period of time. Upon return, if you don't smell gas you MIGHT be OK to turn on the blower.

...then go TROUBLESHOOT the source.

[ndutton]

This happened to me

I don't recall if I posted this before but a few years ago I had this exact sphincter episode.

I was merrily walking down the dock to my boat when about 2 slips away I could detect the distinct smell of gasoline fumes. I thought poor sap, he's got a dangerous condition, hope he doesn't take out the rest of us in the process. By the time I stepped into my cockpit it was clear that I was the poor sap.

First thing I did was step off the boat and turn off the shore power at the dock breaker. Next was to open up the boat as much as possible and start looking for the culprit. I knew anything left on had to be switched off but not haphazardly, it had to be done so no spark was produced. The only things I leave on when I'm not at the boat are the bilge pump (controlled by a float switch) and refrigeration.

I reasoned that the bilge blower switch was located at the very stern of the boat and pretty high. Also the blower itself is mounted high and is supposed to be ignition proof. That seemed like the best thing to get going to evacuate the fumes so I said a little prayer and switched it on. OK, all good. I then turned off the battery switches except for the one feeding the blower. Those switches are supposed to be ignition proof too. That went well.

So, I'd done as much as I could do regarding minimizing an ignition source until I was comfortable the fumes had been exhausted.

Post sortie debriefing
The fuel level in a full tank on a Catalina 30 is a little higher than the carburetor and my float valve had a speck of debris allowing a slow siphon. I have a small catchment below the carb and that was full and overflowing into the bilge although not much reached the bilge. I sponged up the spillage and went after the residue with soap and water.

I admit I'd been too lazy to dig under the quarter berth to close the tank valve which was the real issue. Since that episode I've installed a Xintex MB-1-R fume detector that automatically operates the blower (it's left on when I'm not at the boat) but most importantly I've installed a manual fuel shutoff valve immediately ahead of the carburetor and accessible without opening or removing anything. It's now a routine part of shutting down the engine.

[hanleyclifford]

Good narrative, Neil and we might add that the Coast Guard requires all "inspected vessels", gasoline or diesel, to have a fuel shut off easily accessible to the operater. A needle and seat is the worst possible "shut off" valve.

[weephee]

Gasoline Vapour

Can you give an example of a good fuel shut off valve. I would like to have one on the outlet of my Racor filter. There is one on Ebay, but I really don't want to spend $45 for it. Thanks

[ndutton]

Here's one, 16 bucks plus shipping.

And this is the one I used with an extra port for my fuel purging and polishing system. It also serves as my shutoff valve.

Here are a couple of pics of mine. It's a little hard to see but note the price in the first pic, 6 bucks. Minney's is the greatest.

[jpian0923]

Geez! You guys are scaring me!

If I install a shutoff valve before the Racor, just after the fuel tank, will this prevent a faulty float from emptying the Racor? I have a shutoff just before the mechanical fuel pump but access isn't what I would call great. I mean, I have to lift up the top stair and reach past the hot manifold to shut it down.

[ndutton]

Technically yes, with a valve ahead of the Racor filter it won't empty through a faulty float valve but only because the system is closed or unvented. I'd guess you'd spill some fuel until a sufficient vacuum is created in the Racor to prevent fuel from flowing.

Y'know, with a valve like mine that has a mounting flange you can mount it just about anywhere and plumb a little fuel hose to and from. Mine is about a foot to port of the flywheel and the shaft goes through a bulkhead. A little trick I used was the nameplate is mounted with double backed tape and mounts over the countersunk screw heads that mount the valve. If you don't need or want the extra port you can block it off with a brass pipe plug.

[jpian0923]

I'm thinking about getting one of those and mounting inside the port sail locker for easy access, since most everything I need to close up shop is in that locker anyway. I mean, mainsail cover and shore power cord etc. Thanks Neil.

[weephee]

Gasoline Vapour

Thanks Neil. That's the shut off valve I was looking for only the ebay one I saw was $41.

http://cgi.ebay.com/ebaymotors/?cmd=ViewItem&_trksid=p3984.m1423.l2648&item=220783056442&sspagename=STRK%3AMEWAX%3AIT

Thanks again.
Larry

[ndutton]

Yeah, eBay isn't what it used to be. The deals are more scarce these days and I'd say the auction you referenced is no deal at all.

I've brought this up before and probably shouldn't again except that I like mine so much. If adding a valve, getting the three port valve is a big step toward the automatic filter purging system I have. It requires some additional fuel hose, an electric pump and a little electrical but with it purging the air after changing the fuel filter is a dream (mine's a spin on cartridge type). I can also polish fuel through the filter returning it to the tank and drain the tank into jerry cans easily, all of which I've done.

Something to consider.