You might be on vacation by now, but maybe you'll see this before you get home.
I just installed a water heater this weekend. Scanning the manual, I found the following paragraph. There may have been some lawyers involved with writing this.
<Quote>
Fire and Explosion If Hot Water Is Not Used For Two Weeks Or More
CAUTION: Hydrogen gas builds up in a hot water system when it is not used for a long period (two weeks or more). Hydrogen gas is extremely flammable. If the hot water system has not been used for two weeks or more, open a hot water faucet for several minutes at the kitchen sink before using any electrical appliances connected to the hot water system. If hydrogen is present there will probably be an unusual sound such as "air" escaping through the pipe as hot water begins to flow. Do not smoke or have an open flame or other ignition source near the faucet while it is open.
<End Quote>
My question for the lawyers: What if I don't have a kitchen sink in the building where the water heater is installed?
I believe the hydrogen gas buildup idea is utter b s.
Where would it come from?
Yes, water is 2/3 hydrogen by atom count, but that is bound pretty tightly to the oxygen.
Heat alone won't do it. Electrolysis could, but you need a lot of current and a lot of ion content in the water, neither of which normally exist in a hot water heater. And how would it get out of a hot water heater?
That's a classic. I've had lots of water systems over the years that were not used for weeks or months. Don't recall any volume of gas escaping when used again. Even if there was, it wasn't more than a small burp. Sounds like something someone came up with as joke, to see how stupid the lawyers are.
Yes, I'm on vacation, and now I have to worry about hydrogen gas explosion!!
Maybe so.
Doesn't this apply to people who leave the WH on, as well as off, probably moreso?
I don't remember this.
You should put one in. Otherwise it's negligence
Cindy's link says "2. Normally, you'd be using your hot water often enough that ...". Is he referring to the water that is hot, or any water in the hot water system. I think it's the first one, so it's a good thing I turned off my WH. It might keep my house from going up in smoke when hydrogen gas reacts with my electric sink.
Did I mention my alarm, complete with siren and calling the monitoring company went off the first night. Maybe it could tell the first signs of hydrogen. If not, I have 2 things to worry about. Thanks for the warning.
The dishwasher did come out of the wall, I tracked that story down years ago and will repeat it here shortly.
However it was not hydrogen IMO, and the reaction is not what is claimed. A sacrificial anode system simply does not produce sufficient current flow to produce H2. The voltage difference is dependent on the two metals used, and they don't change during the life of the system.
An impressed current system can theoretically be set too high, causing hydrogen bubbles under the paint of the protected metal (not the anode) and causing the coating to fail and then rust to occur. I've never been able to find a single case of sufficient gas production to be explosive.
Okay, a little more. I can think of two ways to get hydrogen: electrolysis and corrosion. Electrolysis is out. There is obviously not enough charge difference between the magnesium anode and the steel casing to produce that. There is a tiny amount of hydrogen produced as part of the corrosion process, as electrons flow through the metal, then ions through the solution, but it combines immediately into rust.
In the mid 90s the dishwasher explosion was passed to military engineers (I was one back then) as a warning, but with no details other than hydrogen from a hot water heater. The Corps of Engineers maintains a research lab in Champaigne Illinois. I wanted to work there but you had to be a PhD student at U of Ill. I had taken their corrosion protection course and the anode theory didn't make sense, so i called up there and chatted. They agreed, the hydrogen theory didn't make sense, no way to get enough produced from a sacrificial anode.
So I tracked down the story. This took several weeks, there was no internet then, and the military has many layers, but I eventually got hold of the Public Affairs Officer who wrote the story, and from there I got to the Operations and Maintenance Division chief who had responded to the incident. The location was a mothballed housing neighborhood on an Air Force base in Florida. (going from memory) A housing employee was assigned to check each house on a regular basis to make sure nothing was deteriorating, etc. Part of the process was check for leaks, run the dishwasher, etc. When she turned on the dishwasher it exploded, and it did bounce out of its housing. She was not hurt but it did scare her a good bit. I asked the maintenance engineer how he knew it was hydrogen, since I didn't have any Draeger tubes for H2 and I doubted he did. He said he ran hot water in a plastic bag and an air or gas bubble formed on top, he didn't do any chemical checks. We talked a little further, and he related that they had just done a lot of sewer line work in the same area.
Now, if there were a significant amount of hydrogen in the water, it would have to remain dissolved until the dishwasher was turned on, then it would have to have enough of it discharged (come out of solution) during operation, and then an ignition source would have to get into the wet dish compartment of the dishwasher. Hot water doesn't hold much gas - just think of how much CO2 you can keep in a soda bottle, and hot is worse. BUT! The dishwasher is always open to the drain, and if the trap is dry methane can come up into it. Dry trap in an unoccupied house, sewer line work, methane, and spark from turning the dishwasher on (not impossible the employee was smoking, also). This makes a whole lot more sense than hydrogen.
The problem with the sewer gas theory is that I've never seen a dishwasher connected directly to the sewer line. It's always been just below the sink drain opening, which is 4" wide and usually left wide open, so any gas would have an easy path out through a wide opening, versus going through another small drain line to the dishwasher. I suppose you could have the drains stoppered up though.
Two other points. I agree that the galvanic potential doesn't seem enough to generate significant hydrogen. But an electrolysis cell sure can. The tank and magnesium anode form one side of that. If there were another piece of metal in the water, isolated from the tank, some fault in the electrical system, then it could make a lot of gas. But IDK what that other thing could be. With an electric tank, i would expect that the heating element outer metal is bonded to the element metal that bonds to the tank. So I don't see how that could happen either. Also the ignition source for the dishwasher blast remains a mystery. The motor, etc are all underneath, not inside the cavity where the gas would be.
While pure CH4 is lighter than air, sewer gases are a mix of gases, many of which are heavier than air. I can see that collecting in the DW rather than venting, particularly if the sink trap still holds water and there is no air-gap (or the air gap is plugged by insect debris etc, in the abandoned military housing unit).
1 - A housing employee was assigned to check each house on a regular basis to make sure nothing was deteriorating, etc. Part of the process was check for leaks, run the dishwasher, etc.
2 - Dry trap in an unoccupied house...
In a static situation (no sewer line work) one would not expect the trap to be dry in a house that was checked on a regular basis. If the timing was so far apart that the trap water evaporated, then DW's would have been exploding all over the housing complex. At a minimum, there would be sewer gas odors that the inspector would have been reporting.
*Maybe* the "sewer line work in the same area" could have siphoned the kitchen sink dry, but I think that's a stretch. What does "in the same area mean"? Just that house had a dry trap? There was enough sewer gas present to blow up the DW but not enough odor to alarm the inspector? She just went through her normal tasks? Again, seems a bit of a stretch.
*Maybe* this was the first house that she inspected, but if so, one would think that the other houses would then have been inspected for this specific danger. If that was the case, there would be documentation detailing the issues and your maintenance engineer buddy would have told you that.
I think if hot water heaters were really a source there would be a lot more explosions, but I dunno. I also don't know what the planned frequency of these house checks was - monthly, quarterly? nor whether the lowest paid employees assigned to do these checks alone actually did them all.
I know that the dishwasher was destroyed in the explosion, because i actually talked to someone who looked at it. Could the explosion have been underneath or behind? dunno. Sewer gas explosions do happen.
If the sink trap still holds water, the sewer gas can't enter at all, assuming the system vent works. The dishwasher connects to the system after the trap.
Not only more explosions, but there should be a whole lot of people reporting that systems left unused for months, eg vacation homes, had a lot of some gas coming out when a faucet was first opened again. I don't recall having even a burp, unless the system had been drained, worked on, etc.
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