Has this happened to you?

[plumberscrack]

I roughed in the plumbing for a house last year. Alll new waste, vent and water pipe. All waterlines were capped off at fixtures. I filled the electric water heater with water and turned on the electric to make sure it was heating. I mistakingly left the electric on to heater but turned the water off at the main. 6 months go by I come out to start setting fixtures. I check the main valve...still off. The first copper cap on the hot side is too close to the cabinet to cut so I go to sweat it off. There I am under the kitchen sink with a torch when the cap blew off and stuck me square in chest like a bullet. Make that a red hot bullet.:eek: Ok yea the pressure blew it off, I get that, what I don't get is why a 4' flame came shooting out of the pipe.:confused: That scared me more than the cap plunking me in the chest.

[Hondahead]

what I don't get is why a 4' flame came shooting out of the pipe.:confused: My guess is a little residual flux.

[ToUtahNow]

This is a little wierd and hard to explain but yes it has happened to me. It appears when you fill a water heater but do not bleed the air out of the tank the air will become a flammable mix after an extended period of time.

When it happened to me the flame was a fireball of about 60 sq ft but was not a very hot gas. This was in a 2-year old condo which had never been occupied.

The Plaintiff's Expert released pressure from the T&P to show the water would end up in the same drain line as the drain pan. When he released the pressure we ended up with a fireball explosion in front of the water heater.

He called the explosion a delayed ignition caused by the air trapped on top of the heater blowing the pilot away from the burner. I agreed it came from air on top of the water heater but disagreed it was a delayed ignition as the explosion was outside of the water heater. After some research I found an article which explained how the air could turn explosive after an extended period of non-use if not bleed after the heater was install.

Mark

[Bob D.]

Hasn't happened to me, but it's caused by H2 build up in the lines. It can happen in a domestic hot water system in just a couple weeks. Sometimes people coming home from month long vacations have experienced the same thing, though they think it is 'air' in the system it is hydrogen. A smoker could be in for a big surprise.:D

Why does it occur? I think because the electric heating element is acting as a low-efficiency electrolytic anode and creating H2 and O2. We don't normally see enough buildup with daily use for this to be a problem, but when the system sits idle (zero flow) for extended periods the H2 and O2 will build up pockets of gas. The O2 gets -reabsorbed by the water but the H2 remains free, hence the explosive concentration which shoots flames out and burns your butt (or other parts not meant to be toasted :eek: )

[ToUtahNow]

Here is a cut-n-paste from the owners manual of an American Appliance water heater.

HYDROGEN GAS CAN BE PRODUCED IN A HOT WATER SYSTEM
THAT HAS NOT BEEN USED FOR A LONG PERIOD OF TIME
(GENERALLY TWO WEEKS OR MORE). HYDROGEN GAS IS
EXTREMELY FLAMMABLE AND CAN IGNITE WHEN EXPOSED TO A
SPARK OR FLAME. TO PREVENT THE POSSIBILITY OF INJURY
UNDER THESE CONDITIONS, WE RECOMMEND THE HOT WATER
FAUCET BE OPENED FOR SEVERAL MINUTES AT THE KITCHEN SINK
BEFORE USING ANY ELECTRICAL APPLIANCE WHICH IS CONNECTED
TO THE HOT WATER SYSTEM. IF HYDROGEN IS PRESENT, THERE
WILL PROBABLY BE AN UNUSUAL SOUND SUCH AS AIR ESCAPING
THROUGH THE FAUCET AS WATER BEGINS TO FLOW. DO NOT
SMOKE OR HAVE ANY OPEN FLAME NEAR THE FAUCET AT THE TIME
IT IS OPEN.

Mark

[plumberscrack]

Why does it occur? I think because the electric heating element is acting as a low-efficiency electrolytic anode and creating H2 and O2. We don't normally see enough buildup with daily use for this to be a problem, but when the system sits idle (zero flow) for extended periods the H2 and O2 will build up pockets of gas. The O2 gets -reabsorbed by the water but the H2 remains free, hence the explosive concentration which shoots flames out and burns your butt (or other parts not meant to be toasted :eek: )

Maybe I was smoking cigarettes in the stairwell when we covered the properties of hydrogen in chemistry class. So you are saying (correct me if I'm wrong here) that somehow the heating elements separated the hydrogen and oxygen molecules from the water? :confused: I boil water all the time and it never once became flammable. Sounds alot like witchcraft to me. You could be burned at the stake for saying such things.;)

[ToUtahNow]

I'm no chemist but my understanding is the Hydrogen gas is created in the water heaters due to electrolysis caused by the materials the heaters are made out of including the anode. Supposedly all heaters created the gas but in small quantities which are flushed out when you use your hot water. The problem comes in when you have not used your heater in sometime and you have a build up of the Hydrogen.

Mark

[Bob D.]

Mark got it right.

You don't remember the experiment with the inverted test tubes and the battery (http://www.science-projects.com/Electrolysis/eDevice.htm)?

http://www.science-projects.com/Electrolysis/eLysis.htm

[HVAC HAWK]

wow i never heard of that , this was a good learning experience.

thanks

[plumberscrack]

Mark got it right.

You don't remember the experiment with the inverted test tubes and the battery (http://www.science-projects.com/Electrolysis/eDevice.htm)?

http://www.science-projects.com/Electrolysis/eLysis.htm

Wow, You must have gone to an elite school. All we did in chemistry class was make rock candy out of sugarwater and light our farts on fire with the Bunson burners.:D I also remember making electricity out of a potatoe or something.

[Bob D.]

Yep, we had a great chem teacher. I remember making beer, and he gave us a good recipe for easy to make stink bombs from household chemicals. Of course we had to try that out a couple times over the school year, the principle wasn't too happy when he learned where our inspiration came from.

He kept the class interesting and we learned a great deal more thanks to his methods and insistence on jamming some learning into our brains whether we wanted it or not.

[ToUtahNow]

Follow this link and you will see what happens with a little Hydrogen gas from the water heater and a dishwasher.

http://www.cdc.gov/elcosh/docs/d0400/d000435/d000435.html

Mark

[Gene Bickford]

So this gas build up can happen when power to the hot water heater is left on and, the hot water has not been used for an extended period?
Can it still happen if power to the hot water heater is turned off?
Can it happen with a gas hot water heater?

[Gofor]

The separation of H2O (water) into H2 and O2 (the free oxygen molecules will combine) happens due to the electrical current flowing through the water, not from just heat. No electricity, no hydrogen build-up. Gas heat will not cause the water to separate into its basic element components, either.
This reaction is the basis for some of the hydrogen fuel cell technologies being experimented on for automobiles. Igniting the hydrogen/oxygen mixture was used by Goddard to fuel some of his first rockets. It evolved into the liquid fuel rockets used to put man on the moon (they liquified the hydrogen and oxygen in separate tanks and combined them in the rocket motor). Bet you didn't know you had a potential moon rocket in the house, did you?

Go

[ToUtahNow]

The separation of H2O (water) into H2 and O2 (the free oxygen molecules will combine) happens due to the electrical current flowing through the water, not from just heat. No electricity, no hydrogen build-up. Gas heat will not cause the water to separate into its basic element components, either.
Go

I don't know about the gas heaters not having the same problem. The heater where I had it happen was a gas water heater and if you look at the installation manuals of many of the gas water heaters you will find a warning about Hydrogen gas being formed in the heaters.

Mark

[Drip Leg]

Good stuff every plumber should know. Cant say I havent learned anything today hehe.