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Post by silverdragon on Jul 17, 2014 6:56:47 GMT
'Pends on how you stop.
On a hill, difficult, but I was taught how to stop without brakes, engine braking, Exhaust brake, (Jake in USA) then roll to a stop or use light braking for the last bit.
But definitely stop...?...
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Post by wvengineer on Jul 17, 2014 13:59:25 GMT
So, back to the subject of blowing up melons...
My first question is how do you properly instrument a cantalope?
Next thing to do is to find out how much pressure is needed to pop a melon. I would start by injecting compressed air into a melon and read the pressure when it starts leaking. Next, inject pressurized steam to simulate the temperature effects of a fire and see if that affects the numbers. Then repeat with charred rinds.
Another method would be to put a melon in a 500+ F oven and see what happens.
Thinking about it, wouldn't you have to heat a melon rather quickly? If you heat too slowly, you cook it though and then would reduce the strength of the rind, right?
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Post by the light works on Jul 17, 2014 14:01:24 GMT
'Pends on how you stop. On a hill, difficult, but I was taught how to stop without brakes, engine braking, Exhaust brake, (Jake in USA) then roll to a stop or use light braking for the last bit. But definitely stop...?... let me make sure I understand what you are saying: you are saying that if you started down the hill in too high a gear, and the truck overran the engine braking capability such that you caught a brake on fire trying to prevent it becoming a runaway, you could use the engine braking capability to bring it to a stop before getting off the downgrade? that makes you a better driver than my father - he had his brake booster go wonky on a downgrade, once, rendering his brake pedal completely invalid, and it took him about a quarter mile AFTER he got off the downgrade to get the truck down to a speed slow enough to stop it with the handbrake. |
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Post by the light works on Jul 17, 2014 14:03:15 GMT
So, back to the subject of blowing up melons... My first question is how do you properly instrument a cantalope? Next thing to do is to find out how much pressure is needed to pop a melon. I would start by injecting compressed air into a melon and read the pressure when it starts leaking. Next, inject pressurized steam to simulate the temperature effects of a fire and see if that affects the numbers. Then repeat with charred rinds. Another method would be to put a melon in a 500+ F oven and see what happens. Thinking about it, wouldn't you have to heat a melon rather quickly? If you heat too slowly, you cook it though and then would reduce the strength of the rind, right? you can start with injecting your pressure agent, but you have to seal the injection site. as for heating it quickly, you will probably have to go up to a thousand degree oven to better simulate fire conditions. |
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Post by wvengineer on Jul 17, 2014 14:10:19 GMT
Yeah, my question is how to seal the entry hole so that it will hold pressure, but not effect the overall structural strength of the melon?
So we are looking more at a kiln or blast furnace then to the oven test?
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Post by the light works on Jul 17, 2014 14:15:36 GMT
Yeah, my question is how to seal the entry hole so that it will hold pressure, but not effect the overall structural strength of the melon? So we are looking more at a kiln or blast furnace then to the oven test? I'd be inclined to just drop it on a propane crab cooker. |
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Post by OziRiS on Jul 17, 2014 17:29:13 GMT
It might also be interesting to take into account that the situation wasn't created with a single melon. Heating just one melon might give a false result, since we don't know which (if any) melons exploded. It might not be the ones at the bottom of the pile that had direct contact with the fire, but the ones in the middle or on top.
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Post by wvengineer on Jul 17, 2014 21:58:09 GMT
I'd be inclined to just drop it on a propane crab cooker. Deep fried (or boiled) melon. Not sure if that sound yummy or not. Okay, does anyone know how they pack cantaloupes in a truck? I doubt that they are all just piled in there, one on top of another. I have seen large,(~48" cube) heavy cardboard boxes at some supermarket. Is that how they are shipped or just used for display purposes? If those are shipping crates, you have additional fuel at play inside the trailer. You have the card board and wooden pallets that will also fuel the fire. Edit: Looking at the pictures from before, it looks like there is some wood chunks int here as well as cardboard. So that leads me to believe they may have been shipped in the pallet boxes. It also looks like some sort of fibrous materiel by the edges. I am guessing that is insulation from the walls. |
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Post by the light works on Jul 18, 2014 1:50:53 GMT
I'd be inclined to just drop it on a propane crab cooker. Deep fried (or boiled) melon. Not sure if that sound yummy or not. Okay, does anyone know how they pack cantaloupes in a truck? I doubt that they are all just piled in there, one on top of another. I have seen large,(~48" cube) heavy cardboard boxes at some supermarket. Is that how they are shipped or just used for display purposes? If those are shipping crates, you have additional fuel at play inside the trailer. You have the card board and wooden pallets that will also fuel the fire. Edit: Looking at the pictures from before, it looks like there is some wood chunks int here as well as cardboard. So that leads me to believe they may have been shipped in the pallet boxes. It also looks like some sort of fibrous materiel by the edges. I am guessing that is insulation from the walls. yes, they ship in the "skids" |
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Post by wvengineer on Jul 18, 2014 11:31:05 GMT
So if you have a bunch of melons in skid boxes, with a fire underneath, if you burn out the cardboard on the bottom, could that create a chimney effect in the box? Wouldn't that result in the melons getting even hotter?
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Post by the light works on Jul 18, 2014 12:38:28 GMT
So if you have a bunch of melons in skid boxes, with a fire underneath, if you burn out the cardboard on the bottom, could that create a chimney effect in the box? Wouldn't that result in the melons getting even hotter? It is possible. or the skid could protect the melon from the direct heat, preventing premature burn through. |
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Post by silverdragon on Jul 19, 2014 7:11:52 GMT
'Pends on how you stop. On a hill, difficult, but I was taught how to stop without brakes, engine braking, Exhaust brake, (Jake in USA) then roll to a stop or use light braking for the last bit. But definitely stop...?... let me make sure I understand what you are saying: you are saying that if you started down the hill in too high a gear, and the truck overran the engine braking capability such that you caught a brake on fire trying to prevent it becoming a runaway, you could use the engine braking capability to bring it to a stop before getting off the downgrade? that makes you a better driver than my father - he had his brake booster go wonky on a downgrade, once, rendering his brake pedal completely invalid, and it took him about a quarter mile AFTER he got off the downgrade to get the truck down to a speed slow enough to stop it with the handbrake. Again, "Depends". If its full weight 44 tons, or above, you pick a soft spot in the scenery. Lightweight, yes, exhaust and engine braking on a not-too-steep down-slope will slow you effectively. I have always been taught, and always remember, plan for brake fail. Always approach a hill as if you may not be able to stop on brakes. Its quite amazing how much better brakes have become in the last half century, modern drivers "Have it easy", but I remember trucks back from you Grandfathers days, and I hated them. Especially when you start to get tricky.... All this "Depends".... There is a reason, there is no one-size-fits-all answer for every problem, Driving at that level is an art form, planning ahead is key, you know that with your Fire trucks, I bet there are hills you know you absolutely dread trying with a full load?... one or two you would rather go around?... Or do you live in a completely flat area. I know drivers who dread fear Windy Hill. For me, its part of the scenery, I have taken more loads over there than I care to remember. Coming down "Full", yes, I sweat, every time, especially in anything that isnt Dry good conditions, so thats almost every time... But your supposed to worry. The day you dont is the day you fail. Windy hill on brakes, you pump them slowly. You must give them periods of "off" to cool down. If you ride the brakes all the way, you have, at the foot, a pile of smouldering scrap metal. I have gone down that hill at a crawl holding it in low gear just so I dont overheat the brakes. It annoys the crud outa motorists who expect you to be doing top speed down there... but hey, its my job, annoying roller-skate drivers. Slow down before the top, pick a gear, stay in it, and stay in it all the way. You and I know this, Rollerskate drivers are reading this and wondering..... why.... |
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Post by the light works on Jul 19, 2014 11:41:59 GMT
we don't have any truly bad hills in our response area. the worst is the hill going out of town to the north, and that is shallow enough that I climb and descend it at 55 MPH+ in my work truck. the bigger engines have a bit of trouble going up it because they only carry 360 HP (not built for cross country transport, after all - its pretty extreme for us to be running 60 MPH through town.) but the brakes are more than generous enough to compensate for bad gear selection on the downhill side. - but we do get a lecture if we bring one within nose-shot of the mechanics with hot brakes.
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Post by mrfatso on Jul 19, 2014 15:05:50 GMT
Windy Hill is quite infamous in the UK, it's part of the M62 Motorway crosses the Pennines Hills that run down the spine of Northern England.
Though it's nothing compared to the Hill just west of Minehead, Porlock Hill, which is a bit of a car killer.
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Post by the light works on Jul 19, 2014 18:32:20 GMT
Oregon has a few hills bad enough to have a runaway truck ramp, and one or two bad enough to have more than one ramp. - but not like states on the continental divide - where one interstate has a downhill speed limit of 25 MPH for trucks. (I forget the grade percentage)
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Post by Cybermortis on Jul 19, 2014 19:55:41 GMT
None of which has anything to do with the OP.
Back on topic please.
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Post by the light works on Jul 19, 2014 22:50:36 GMT
None of which has anything to do with the OP. Back on topic please. right. so our current variables are rate of heating, whether direct flame impingement makes it better or worse, and whether a melon in the middle of a crate might blow up when a single melon wouldn't. |
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Post by Cybermortis on Jul 19, 2014 22:56:22 GMT
So testing should be with a single melon, then with a number of melons packed together in a wooden crate (or whatever they are shipped in).
Only concern is wastage, MB will probably not want to waste a lot of food running these tests (a couple of melons is probably fine, but a truckload is pushing things). To make things worse using out of date melons is probably not going to give the correct results, as they are likely to have dried out to some degree.
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Post by OziRiS on Jul 19, 2014 23:32:13 GMT
So testing should be with a single melon, then with a number of melons packed together in a wooden crate (or whatever they are shipped in). Only concern is wastage, MB will probably not want to waste a lot of food running these tests (a couple of melons is probably fine, but a truckload is pushing things). To make things worse using out of date melons is probably not going to give the correct results, as they are likely to have dried out to some degree. You wouldn't need an entire truckload. Just enough to fill a space of 3' x 3' x 6' (approx. 1m x 1m x 2m). I can't imagine that heat spreading sideways would have more of an impact than heat going up, so the biggest factor here would probably be creating a chimney effect. I think heating them in an enclosed space would also be a factor in replicating the circumstances, since the original story is about a trailer catching fire. It's not just a crate sitting out in the open. To be fair, we should probably also note that "an explosion" doesn't neccesarily have to be something spectacularly violent that decimates the entire trailer. The original story talked about people being able to "hear the cantaloups explode", so clearly hearing an audible pop at a reasonable distance should be enough to confirm it. Remember, they're not packed with C4, so it's reasonable to assume that any explosions wouldn't be overly extravagant, but there is a chance they'll become small pressure vessels and do more than just quietly rupture and let out steam. That's what we're looking for. |
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Post by the light works on Jul 19, 2014 23:45:53 GMT
right - audible "pop" I'd be inclined to use a (as I said) propane crab cooker for the heat source - and possibly a dryer drum for the "pile" test. - and I think past date melons would be acceptable for the bulk testing.
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