Opinion: propane and lower explosive limit -photo 1

[OKD30]

Hi All-

Just looking for a general consensus here..

Any possibility that a BBQ grill (5 gal propane tank) running 1/6 knobs wide open for several hours, lid open or closed while without active flame could reach the LEL on this deck if ignition were introduced into the environment? Assuming minimal wind..

(Exclude Scenario in which built-in BBQ ignition were later activated while closed- as clearly LEL reached here)

Thanks so much- photo is setting attached (open on three sides)

 

[Compositepro]

Almost zero possibility. The burners are design to mix air with the propane to get a combustible mixture, this mixture is heavier than air and will sink to the floor while getting further diluted. Then it will roll off the floor to the outside. Any draft or wind will greatly disperse the propane. The worst that could happen is that you get a whoosh of flame near the grill, as you do if you wait a minute to light the grill after turning on the gas.

 

[EdStainless]

The LEL is only 2%, you might want to make sure that there is a way to disperse the gas.
A whoosh near the grill means that the person lighting it just had their clothes go up in flames, not fun.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[MJCronin]

I gotta ask this ...

Why are you asking this question and showing your home ??

Is this to settle some kind of bet ???

MJCronin
Sr. Process Engineer

 

[miningman]

Well I for one would not ever stake money..... never mind my life... that LEL could not be attained under the right circumstances. I know of one instance where a major incident occurred at minus 40 degrees.... which is very close to the boiling point of propane........and the event initiated at the lower elevations of the general area. Dunno if it was a detonation or just a fire , but there were serious injuries and damagae.

 

[LittleInch]

Possibility - yes, but depends a lot on external temperature, wind etc and what's in the way.

You could easily get a significant pocket trapped at low level around the kitchen area especially at low level.

Explosive gas concentrations are strange things which you don't want to mess with. E.g. if your minimal wind was in the direction of the wall then it could back up the gas into that corner.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

@LittleInch,

take Compositepro observation into account: Its not leaking pure propane, its "leaking" the mix from the burner. Here we already have a air/fuel mix and further dillution will quickly disperse below LEL? I think that sounds very plausible.

Best regards, Morten

 

[LittleInch]

True, but is this mixture stable?

I don't think it is. So sure, at the burner tip you have a good mixing, but if it's not burning does that mixture stay like that.

I suspect you will get an increase in density.

Besides, I'm sure I'm not the first person to get a good "whoomph" when trying to light a propane oven.

It might not "explode", but it sure will create a fireball.

So, possibility low to very low. Consequence high to very high. Result - low to moderate risk.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[1503-44]

6 knobs on for several hours. There will be an explosive atmosphere somewhere between burner tips and floor. BW you get that condition with one knob on. That's how you light the things. I get it all the time when I run the hot water first before I use my stick lighter on the pilot of my propane bottle fueled water heater. Run the experiment.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[3DDave]

Considering the rarity of such explosions, it seems unlikely. Most are where the gas is confined with walls, such in houses and food trucks.

I agree there could be a flash and light materials might ignite - clothing, tablecloths, loss of eyebrows and hair, but not explosive detonation - the porch will still be there and not splintered.

It's a situation similar to spilled liquids with low-lying vapor; makes quite the show but not a problem where it's not enclosed or the liquid splashed on people.

I'd be more concerned about a failed fitting (usually user error in installation) on the tank leaking directly. I don't see a tank so is it in an enclosed volume? That situation could detonate.

What would one expect to do about this besides don't do it?

 

[1503-44]

Agreed, however the criteria should not be an explosion inside a semi-confined area. Neither your wife, guests, insurance company and plastic surgeon will be very impressed with your engineering abilities should it flash during your next birthday party. If you can't remember to turn off the gas, perhaps a beeping alarm on flameout would work for you.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[EdStainless]

I know someone with a mostly-indoor grill (room with 3 solid walls). He used a 90deg turn supply/shutoff valve. There is a flap (hinged metal tab) that you have to lift to turn the gas supply on and it cannot drop back down with the valve open because of the handle geometry. When lifted this tab turns on power to an igniter. So there is contentious ignition whenever there is the possibility of having fuel. It also turns on an indicator light.
Yes you have to tolerate the clicking, but it isn't that loud and it works.

= = = = = = = = = = = = = = = = = = = =
P.E. Metallurgy

 

[Compositepro]

"but is this mixture stable?". Gasses of of any density will not naturally separate once mixed. Diffusion of molecules always keeps them mixed. In fact, any gasses in a sealed container will eventually become perfectly mixed even if they start out completely segregated.

 

[1503-44]

Gas detector $45

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[1503-44]

Reverse the flame alarm circuit

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"

 

[3DDave]

I misread that link title for a moment and thought is was using flame as an alarm for a clock.

WAKE UP!

 

[1503-44]

Nothing wakes you up quite like your alarm clock on fire.

“What I told you was true ... from a certain point of view.” - Obi-Wan Kenobi, "Return of the Jedi"