Poppin Manholes !

The original "Out of Towners" Movie (with Jack Lemmon, not Steve Martin) contains a great scene of an exploding NY manhole cover that barely misses JL on the way down.

Beachcomber

It must be the human flatulence that collects underground

probably};-) i think they should install a vacuum vent system and process what ever it is.,

i remember once was about 20-30ft when one exploded, I saw the lid fly past the front of a white 4dr sedan about +-25ft up in the air, landed about 7feet away from it, the manhole was about 1=BD feet from the front bumper., it was exhilarating. no one/thing got hurt.

darn near dangerous ! };-)

if you let off a gigawatt of power in a microsecond in an enclosed vault you get boom

We used to throw cherry bombs in storm drains and every once in a while we could get something going but it was never much more than rattling the covers. At night you could see a blue flame coming out of the drains. It was impressive if you could get about a half mile of storm drain to go tho. ;-)

I'm guessing with lots of fumes accumulated over time in such a close environement with high tension wires a tiny spark of that magnitude would set it off.

It's always happening in one place or another around nyc.it could lift off a car and toss it badly if doesn't blow it up completely.

Not really. It is simply arc flash energy. It usually has nothing to do with fumes.

Charles Perry P.E.

Charles: are you saying that only the arc flash causes the explosion that blows off the covers in Manhole Explosions?

I was told it was due to accumulated gaseous fumes and perhaps the arc flash, and that makes sense an electrical spark (arc) alone could do it., it has to involve igniting a gas of some sort.

No it doesn't. Haven't you ever seen short circuit tests of medium voltage (or even 480V) equipment? A 480V short in a large panel can blow the doors off. Of course the switchgear manufacturers are always testing and improving their designs to try to contain the arc flash inside the switchgear and vent the pressure elsewhere. Why do you think OSHA is now requiring arc flash calculations for all switchgear installations now?

A high current arc flash vaporizes the conductor. That creates a tremendous amount of pressure in enclosed spaces. Plenty of pressure to pop a manhole cover.

Charles Perry P.E.

I'm not buying it. I don't see it that way either, an arc flash would tend to weld (or draw) everything in it's way, given, that creates some pressure but not enough to blow the lids, by means of gas igniting in the Blast the pressure would double or triplicate Then causing the Manholes to fly off. [sometimes several in a line as the last case in bklyn]

Do you work for Con Ed or a Utility Company ? i don't like to speculate with theory over the harsh contending facts. your theory covers one manhole poppin but not two n three blastin off simultaneously.

!!!!!!!!!!!!!!! You are completely and utterly wrong.

Charles Perry P.E.

Charles Perry P.E.

"A 10,000 A arc at 480 V is equivalent to 8 MW or approximately eight sticks of dynamite"

So, you're claiming 8 sticks of dynamite can lift a manhole cover?

;-)

(Count me *out* of that experiement.)

As amazing as it sounds, yes I do believe 8 sticks of dynamite could lift a manhole cover ;-) Imagine 10,000 A at 12kV.

Charles Perry P.E.

!!!!! Here you go Mr. Charles iL Instant Wizard !!!!!

They're installing a HV Network Protection Unit on my block, so, I talked with some Guys from Con Ed and they corroborated this.

I've got a website too }:-)

=F7=F7=F7=F7=F7=F7 Utterly Watt ?????

Charles Old Boy }:-) TNT ? It probably can., But, You've gravely underestimated me. my bible for the past 30 years is the American Electricians Handbook, by/Croft:)

so, I know how electrical stuff works pretty well ~> thanks for your input to this topic though, your ref; website's real pro and cool., didn't say anything about manholes specifically. WATT A BLAST !!! I'm sure it's not the last we hear of them.

Your statement is still wrong. You said "an arc flash would tend to weld (or draw) everything in it's way". That is completely and utterly incorrect. Anyone who believes that has no business working around electricity. They are endangering themselves and others.

As for the "how stuff works" article. It got it half (almost anyway) right. There are explosions that involve a buildup of gas. There are also explosions in which no gas buildup is involved. We have been blowing up manholes since 1994 at our Lenox MA test lab. Con Ed has the results, but it is not unusual for the line personnel to be unaware of the results.

Even in cases where gas is involved, as much as 50%[1] of the energy is from the arc fault.

Charles Perry P.E. [1] "Underground Event Workshop: State-of-Science Workshop Report", EPRI,

You are just being stubborn and refuse to admit when "You" are wrong.,

An Arc Flash; to begin with, is just that, a flash of energy that occurs when electrons are drawn from another object, it's not Like a Flash Point in a Fire, when the fire flashes over to already heated and moisture free areas. Since the system is held down or originates at some point when the flash occurs, a Large Draw at the Atomic level from a Highly Charged Cathode in this case the HV Cables towards the Fixed Box (gas particle filled) structure, since the surrounding area cannot merge towards the Cables the Arc Occurs through ether, or air facilitated by the Gas or inversely charged particulate matter surrounding the event.

You say you work with electricity, but, don't believe it tends to draw or attract any lofty objects or bodies nearby BEWARE ! you are the one endangered and your advice is lacking in truth and all good conscience., that, concerning All Electrical Phenomenon.

You are an idiot. Arc flashes can blow manhole cover off. They blow the doors off of medium voltage switchgear. You really should research the subject some before you post any more.

Charles Perry P.E.