Boiler explosion caught on nanny cam

what causes this type of explosion?

Wonder if flooding occurred after.

FWIW,

I've seen quite a few dry fired, or little water fired boilers. None of them exploded. They just cracked from overheating.

In the above case, the high limit control should have shut down the boiler before it got too hot. A good reason for a additional high limit control with a manual re-set. Like commercial boilers are supposed to have.

Consider this. A cubic foot of water equals 7 1/2 gallons of water. Water under 12# pressure boils at 244 degrees. That same cubic foot of water at 28# of pressure boils at 296 degrees. The expansion rate as I understand it will cause the cubic water to convert to 1200 cubic feet of steam. If the high limit fails and doesn't shut off the burner, a brand new fill valve operating at 12# PSI isn't going to add water when the system is at 25+ # PSI. The bigger concern is when the relief valve opens when the boiler pressure reaches 30# and starts to relieve. The pressure in the boiler drops, and the entire water content of the boiler converts/expands to steam.

When watching Mythbusters blow up a water heater, It was the drop in pressure below the temperature that causes the explosion. Or the tank rupturing.

A few weeks ago, someone posted an album of steam boiler explosions. Quite stunning.

RobG said:

I'd love to find out what the final verdict is of the cause!

There's a good chance that there will be some element of truth to what happened. You might need a magnifying glass to find it though.

icesailor said:

FWIW,

I've seen quite a few dry fired, or little water fired boilers. None of them exploded. They just cracked from overheating.

In the above case, the high limit control should have shut down the boiler before it got too hot. A good reason for a additional high limit control with a manual re-set. Like commercial boilers are supposed to have.

Consider this. A cubic foot of water equals 7 1/2 gallons of water. Water under 12# pressure boils at 244 degrees. That same cubic foot of water at 28# of pressure boils at 296 degrees. The expansion rate as I understand it will cause the cubic water to convert to 1200 cubic feet of steam. If the high limit fails and doesn't shut off the burner, a brand new fill valve operating at 12# PSI isn't going to add water when the system is at 25+ # PSI. The bigger concern is when the relief valve opens when the boiler pressure reaches 30# and starts to relieve. The pressure in the boiler drops, and the entire water content of the boiler converts/expands to steam.

When watching Mythbusters blow up a water heater, It was the drop in pressure below the temperature that causes the explosion. Or the tank rupturing.

What happens when a boiler dry fires because the autofill is clogged and then during it, for some reason the autofill opens?

I'd bet even the pressure relief can't handle that much volume.


EDIT : I just noticed you kind of covered this, but are you 100% sure a broke autofill could not start under those conditions? I have no idea how they work.

From the video, the relief valve looks ancient.

Hard to believe that even nowadays, people think gas boilers do not need to be serviced once a year.

What if a child were injured?

AlCorelliNY said:

From the video, the relief valve looks ancient.

Hard to believe that even nowadays, people think gas boilers do not need to be serviced once a year.

What if a child were injured?

Ancient, and maybe not a 30# relief valve. Like maybe a pressure only valve for potable water. Way higher than 30#. The test lever is broken with a nail through it. It looks like it had been weeping from the rust on the inside of the valve.

I can hear the dialog. "I don't want to call someone to service the boiler. They all try to rip me off. Like the last time, 10 years ago, who told me I needed a new relief valve. Can you imagine? He tried to rip me off."

When the insurance company gets done "Adjusting" for age, They'll give him $100.00 towards a new boiler. What it might have cost to have someone go over the boiler and replace the relief valve.

Safe money says that the boiler was overheating long before the explosion. And Homeowner didn't want to get ripped off by someone. Selling him something he didn't need. He can afford a Nanny for his precious wonder. But can't afford to have his boiler serviced. Like he does all his new cars.

Gives a whole new meaning to;
"Back slowly out of the boiler room".