Interesting how we take so many things for granted. Sunshine, warm breezes, summer nights, breathing. Wait a minute, what's this breathing all about? It's a fact that we all breathe. Without life sustaining oxygen, we'd all be at Davy Jones' Ball.
Our air is comprised of about 21% oxygen. That's what it takes to breathe naturally. When the percentage goes down to 16% or so, breathing gets to be a chore. And as the oxygen percentage gets lower, so do we, until we are rendered unconscious, and ultimately lifeless, by a thing called anoxia, which means lack of oxygen.
On a vessel, air is not usually a problem. There's plenty of it, and it all contains about the right amount of life giving oxygen. But, there may be a sinister figure waiting to sneak in and take your breath away. It is called carbon monoxide. Tasteless, colorless and odorless, it silently steals into your living spaces, and infiltrates your body through your lungs and into your blood stream. There it inhibits the blood from carrying oxygen, and if not caught in time, sends you to shake hands with Davy Jones and other long lost sailors.
At mooring or anchor, and on deck, is no guarantee that carbon monoxide poisoning won't pay a visit. Adjacent boats, running their engines, can send your carbon monoxide levels sky high. Generators running, with the exhaust reentering the vessel through hatches, ports, or other openings has resulted in death. A group of boaters, happily rafting up off Catalina, were enjoying a day of fun and sun. Maybe too much fun in the sun, as a number of participants complained of headache, nausea, dizziness, mental confusion or fatigue. One of the boaters recognized that something was very wrong, much more than too much beer and sun. Suddenly, the droning of the generators on the rafted up boats made her realize this was carbon monoxide poisoning! Had there not been a combination of her sharp observations, a fast run to Los Angeles, ready paramedics and the availability of a hyperbaric chamber, this trip would have had a tragic ending. Luckily, all survived.
Carbon monoxide is a silent killer. It has no warning properties. High concentrations may cause only transient weakness and dizziness before death. Longer term exposure results in one or more of the symptoms described above. Carbon monoxide poisoning is cumulative, meaning lower concentrations over hours or days can result in poisoning.
Prevention is much better than cure. The first line of defense is a good carbon monoxide detector. There are a number available, but those built to withstand the marine environment are best. Good cabin and bilge ventilation with fresh air, and an exhaust system, free of leaks, that disperses the exhaust well behind, or off to the sides of the vessel, are other safeguards.
Stop the silent killer on your vessel before he stops you. Be aware and be prepared.
Safe Boating.
Showing posts with label ventilation. Show all posts
Showing posts with label ventilation. Show all posts
Saturday, December 6, 2008
Thursday, August 28, 2008
EXPLOSIVE NEWS
It's two-thirty on a warm August afternoon. The operator of a new 27 foot express cruiser, with three passengers aboard, has just finished fueling, loading 80 gallons of gasoline into his tanks. He closes the tank fill, and runs his bilge blowers for four minutes. The gasoline smell lingers, but he's sure it must be from the tank vents and the fuel dock. He starts to turn the key, hesitates a second, and fires up the engine.
Later, from the burn ward at the trauma center, he says he never heard or saw the explosion that threw him into the water, killed one of his passengers, and severely injured the other two. Nor did he see the ensuing fire that destroyed his boat and damaged the fuel dock and two adjacent vessels. "What went wrong?", he asks. "I ran the blowers like I should and still the boat exploded."
This captain broke the cardinal rule of safety on gasoline fueled boats. He didn't lift the hatches, look and sniff, to be sure that fuel hadn't leaked into the bilge. In his case, a loose clamp on the single clamped fuel fill, had allowed several gallons of gas to run into the bilge, where it vaporized and ignited when the engine was started.
Gasoline is strange stuff. A mixture of aliphatic hydrocarbons, it has a flash point of minus 50 degrees Fahrenheit (-50F). So, even in the coldest temperatures, it'll still burn. It's vapor density is three to four times that of air, which is why fumes find the lowest point of your boat, the bilge. It has a lower explosive level of 1.3% and an upper explosive level of 6%, meaning that when mixed with plain old air (vaporized), anywhere between those percentages, and given an ignition source, it's gonna blow. Autoignition temperature is 536 F to 853 F, so if you heat it up on a hot manifold, poof!
So, what can you do to reduce the potential for an explosion and fire? There are a few ways. First, before you start those engines, or generator, raise the hatches, get down below and take a good sniff. There should be no odor of gasoline in a properly maintained vessel. Second, regularly check all fuel system hoses and clamps. All fill line fittings should be double clamped at the tank and deck fitting. Vent hoses should be double clamped at both ends. Damaged hoses should be replaced immediately. Third, be sure your blowers are adequate, properly connected, and draw air from the lowest points of the bilge to exhaust any possible vapors. Finally, consider investing in a vapor detector or "sniffer" for your bilge. They're invaluable sentries when you're underway, and can't sniff the bilge for yourself.
My personal story had a much happier ending than the one above. Returning to the dock after an afternoon cruise on my sportfisherman, I climbed down from the flybridge to the main deck, where I smelled the strong odor of gasoline. I thought one of my neighboring boaters was filling an outboard tank, but this was even stronger. The odors seemed to be coming from my bilge. I opened the hatch to find the port tank had ruptured, and the bilge awash in gasoline. I won't bore you with the cleanup details, nor the precautions we took to preclude ignition, but there were many. The important thing is that there was no explosion or fire. I always run with the ventilation blowers on. I feel it provides an extra margin of safety, and in this case, the blowers likely kept the vapors minimized until the engine was shut down, and all electrical circuits de-energized. Cheap insurance, replacing a blower every two or three years.
Explosion and fire is a terrifying ordeal on shore, more so aboard. Protect your vessel, and your life, by practicing safe fueling, ventilation, and fuel system maintenance.
Safe Boating.
Later, from the burn ward at the trauma center, he says he never heard or saw the explosion that threw him into the water, killed one of his passengers, and severely injured the other two. Nor did he see the ensuing fire that destroyed his boat and damaged the fuel dock and two adjacent vessels. "What went wrong?", he asks. "I ran the blowers like I should and still the boat exploded."
This captain broke the cardinal rule of safety on gasoline fueled boats. He didn't lift the hatches, look and sniff, to be sure that fuel hadn't leaked into the bilge. In his case, a loose clamp on the single clamped fuel fill, had allowed several gallons of gas to run into the bilge, where it vaporized and ignited when the engine was started.
Gasoline is strange stuff. A mixture of aliphatic hydrocarbons, it has a flash point of minus 50 degrees Fahrenheit (-50F). So, even in the coldest temperatures, it'll still burn. It's vapor density is three to four times that of air, which is why fumes find the lowest point of your boat, the bilge. It has a lower explosive level of 1.3% and an upper explosive level of 6%, meaning that when mixed with plain old air (vaporized), anywhere between those percentages, and given an ignition source, it's gonna blow. Autoignition temperature is 536 F to 853 F, so if you heat it up on a hot manifold, poof!
So, what can you do to reduce the potential for an explosion and fire? There are a few ways. First, before you start those engines, or generator, raise the hatches, get down below and take a good sniff. There should be no odor of gasoline in a properly maintained vessel. Second, regularly check all fuel system hoses and clamps. All fill line fittings should be double clamped at the tank and deck fitting. Vent hoses should be double clamped at both ends. Damaged hoses should be replaced immediately. Third, be sure your blowers are adequate, properly connected, and draw air from the lowest points of the bilge to exhaust any possible vapors. Finally, consider investing in a vapor detector or "sniffer" for your bilge. They're invaluable sentries when you're underway, and can't sniff the bilge for yourself.
My personal story had a much happier ending than the one above. Returning to the dock after an afternoon cruise on my sportfisherman, I climbed down from the flybridge to the main deck, where I smelled the strong odor of gasoline. I thought one of my neighboring boaters was filling an outboard tank, but this was even stronger. The odors seemed to be coming from my bilge. I opened the hatch to find the port tank had ruptured, and the bilge awash in gasoline. I won't bore you with the cleanup details, nor the precautions we took to preclude ignition, but there were many. The important thing is that there was no explosion or fire. I always run with the ventilation blowers on. I feel it provides an extra margin of safety, and in this case, the blowers likely kept the vapors minimized until the engine was shut down, and all electrical circuits de-energized. Cheap insurance, replacing a blower every two or three years.
Explosion and fire is a terrifying ordeal on shore, more so aboard. Protect your vessel, and your life, by practicing safe fueling, ventilation, and fuel system maintenance.
Safe Boating.
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