Relief Valve

Thunderbird Road and 38th Street. The damaged home will most likely have to be torn down, authorities said.

It appeared that the homeowner and the man renting the house had been trying to fix the water heater, which may have contributed to the heater being launched across Thunderbird Road and landing near a bus stop, Phoenix Fire Captain Sam Richardson said.

The man inside the home had been renting the house for only about 12 days. Damage to dental equipment he had in the home may be in the tens of thousands of dollars, Richardson said.
Foul play was ruled out, and the incident appeared to be accidental, he said. However, due to the destructive nature of the blast — which also caused minor damage to several nearby homes — the Phoenix police Bomb Squad and the Bureau of Alcohol, Tobacco and Firearms were on the scene as investigators worked to find what caused the explosion. Richardson said the aftermath of the explosion left the house “leaning” to one side.

Jake Brown was sleeping in his room across the street from the house when the explosion occurred.

“All I heard was a big boom and my window shattering,” said Brown, 16. “It shook the whole house.”

Brown said he originally thought a car had crashed into his house. He added that if he had not had his window blinds, the shattered glass might have hit him.

The man inside the home said the explosion “felt like an earthquake,” according to Richardson.

Bill Lee, a salesman with California-based Water Heaters Only, Inc, said water-heater explosions are extremely rare, adding that he has only heard of one other similar incident in his 10-year career. Lee said the explosions usually involve both operator error and a technical malfunction within the tank.

“(The safety valve) should activate at some point way before (the heater) turns into a missile,” he said. He added that homeowners should check their water-heater safety valve at least once each year.

The force even blew through a cinder block wall and ripped a hole in the wall of the neighboring house.

There reportedly was one person in the home at the time of the explosion. The Phoenix Fire Department said that man told them there was no gas connected to water heater. Southwest Gas confirmed that and said there is no gas to the house, which means the explosion was not gas related.

A plumber told 3TV it's possible that too much pressure built up in the water heater and the pressure-relief valve wasn't working properly.

ATF crews and bomb squad investigators are also on the scene to try and determine exactly what happened. A firefighter on the scene, who said he'd never seen anything like this, told 3TV that having those personnel on site is procedure when there's such a large explosion.

People reportedly felt the explosion as much as a mile away.

Potable water boilers, water heaters and storage tanks are limited to a maximum temperature of 210°F. Most of them supply water in the range of 120 to 140°F. Therefore they can make use of pressure-temperature type relief valves for overpressure protection.

The pressure-temperature relief valve provides an extra level of safety in helping to eliminate the steam explosion hazard. Temperature controls (limit switches, gas valves, heating element thermostats, etc.) need to be regularly checked and properly maintained.
But pressure-temperature relief valves can back up temperature limit controls in the event of control malfunction, runaway firing conditions, corrosion and pressure transients.

Regardless of the safety valve type, they need to be installed correctly and tested annually. With a little bit of attention to this equipment, we can all look forward to an uneventful and pleasurable hot shower- especially critical for those of us who need reviving some mornings!

How can I tell if my water heater is at risk of exploding?

As we mentioned, most water heaters operate safely 24 hours a day, 365 days a year. Here are some simple guidelines and warnings for water heater safety:

If it's been more than a year since you Temperature - Pressure relief valve has been tested you should test it. T & P valves are mechanical devices which means that they can fail or clog.

This device is your last line of defense in case of a thermostat failure resulting in overheating of your tank.

It does not matter how old your water heater is. The tank in our video was purchased new just for this demonstration.

Sputtering and spewing from your faucets as you turn them on could be a sign of your water heater overheating. This is especially true if the water heater has been sitting idle for a while.
The spewing/sputtering can occur on either the hot or cold side of your faucet.

Excessively hot water is a sign of a thermostat malfunction, a precursor to excessive pressure build up.

A dripping or trickling T&P valve can mean that your water heater is overheating or over pressure.

What made the water heater explode in the video?

We used a new, 12 gallon water heater (typically, water heaters in homes are at about 4 times this size)

For heating, we used a standard, 4500 watt heating element.
We began with 0 (zero) pounds of pressure.
Could also have used a Natural Gas water heater . It does not matter what heats the water; gas, L.P. gas, electric or oil.

Typical homes have between 40 and 80 pounds of pressure.
As water heats, it expands which results in a pressure increase.

In our demonstration, it took about 1 1/2 hours to rise from 0 to 410 psi which is the pressure at which the tank exploded.
The water temperature was about 400 degrees.

When the tank ruptured, the water erupted into a steam explosion.

These are the same conditions that could exist if your thermostat became stuck "on" and your T&P was faulty.