Pyrophoric carbonization

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mbrooke

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What causes this? Can an energized staple or J-box in a wood frame building cause the wood around it to carbonize?
 

102 Inspector

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Pyrophoric carbonization can also be cause by light bulbs placed too close to lumber causing the continual drying of the material. this lowers the ignition point of the lumber to tinder type qualities. Older homes may have chimneys that do not have proper clearance to framing members. The continued drying of the framing lowers the ignition point to where a chimney fire could easily be started without direct flame involvement. Fire investigators love to try to determine this one at the scene.
 

mbrooke

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Pyrophoric carbonization can also be cause by light bulbs placed too close to lumber causing the continual drying of the material. this lowers the ignition point of the lumber to tinder type qualities. Older homes may have chimneys that do not have proper clearance to framing members. The continued drying of the framing lowers the ignition point to where a chimney fire could easily be started without direct flame involvement. Fire investigators love to try to determine this one at the scene.

That's a good point, I have seen 40 watt dual bulb fixtures with 100s and the wiring is in very poor shape. Ditto for the box and wood frame.

When 120 volts is faulting to wood, how long does it usually take for the wood to turn to charcoal?
 

don_resqcapt19

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What causes this? Can an energized staple or J-box in a wood frame building cause the wood around it to carbonize?
You would have to have enough current flow to heat the wood to have pyrophoric carbonization. I don't think it occurs unless you have raised the temperature to 200?F or greater.
I doubt that even wet wood would be conductive enough for the current flow to create enough heat to cause this.
 
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I have mentioned this before. Back before cell phone cameras, way back when nobody carried one 24/7, I came across an energized K&T during a remodel. The cut end had been shoved back into the wall space at some time. It rested against a 2x4 that had a tear dropped black mark burned into the wood.
 

mbrooke

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You would have to have enough current flow to heat the wood to have pyrophoric carbonization. I don't think it occurs unless you have raised the temperature to 200?F or greater.
I doubt that even wet wood would be conductive enough for the current flow to create enough heat to cause this.

But surely some current must flow? That trickle current would dry the wood out over time?
 

junkhound

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400 or 500 uA (yes MICRO, e-6 amps) is sufficient to cause tracking to start and tree on any surface, even Teflon, glass, and glazed ceramic. Have run tests on everything from Torlon and Teflon to glass and bakelite and even wood.

Basic process is that the conductive moisture film (even condensed fog) on something like TFE or polyimide conducts a few hundred uA when there are any contaminates. When the film breaks on something hydrophobic like TFE, or a section dries out like on wood, the first point of the high resistance current break arcs and carbonizes a tiny spot. This spreads on repeated wet dry cycles. Can take months or years for 120V in a seldom wet environment, at 480V where there is fog it can happen in weeks. Testing where a continuous spray and dry cycle is applied, the time to track between cm separations at 500 Vdc is only minutes. Faster above paschen minimum voltages.

On materials like glass and Teflon, the surface is just etched and no carbon path is created, just craters for more contaminates to collect over time, which may have organic materials that can create a conductive path (typically years). Any organic insulator will track. An IEC test for this is comparative tracking index, CTI.
 

GoldDigger

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Here's a dollar, go get a clue and bring me back the change :roll:


AFCIs save lives.
Leaving said for the moment the question of whether AFCIs save lives (and whether the GFCI component of AFCIs that have them) save lives, there is no way that the AFCI component which would detect the low current micro arcs associated with pyrophoric carbonization.
But a pure GFCI might!
macmikeman is correct.
 

DeltaFarce

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Leaving said for the moment the question of whether AFCIs save lives (and whether the GFCI component of AFCIs that have them) save lives, there is no way that the AFCI component which would detect the low current micro arcs associated with pyrophoric carbonization.
But a pure GFCI might!
macmikeman is correct.
macmikeman is usually correct and awesome at just about everything, except boogie boarding.
 

macmikeman

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Leaving said for the moment the question of whether AFCIs save lives (and whether the GFCI component of AFCIs that have them) save lives, there is no way that the AFCI component which would detect the low current micro arcs associated with pyrophoric carbonization.
But a pure GFCI might!
macmikeman is correct.

Correction- macmikeman is always correct :thumbsup:
 

mbrooke

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Here's a dollar, go get a clue and bring me back the change :roll:


AFCIs save lives.


How do you know AFCIs will stop that? If the current is only micro or milli amps no AFCI will trip on arc currents at that level, assuming an arcing signature is even present.


Further, AFCIs don't trip on glowing connections.
 

mbrooke

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Leaving said for the moment the question of whether AFCIs save lives (and whether the GFCI component of AFCIs that have them) save lives, there is no way that the AFCI component which would detect the low current micro arcs associated with pyrophoric carbonization.
But a pure GFCI might!
macmikeman is correct.


Which makes me wonder, are charred studs from over driven staples really the cause of violent arcs (phase to ground/neutral) or is it low level current leakage into wood?
 

romex jockey

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That pyrophoric carbonization has been witnessed w/o power in a dwelling by fire forensic engineers elevates the phenomenon past the old staple theory.

But this is less than the magic it appears, if one considers our (American) grounding system proliferating to the point where Mr Kirchoff's rules come into the equation

~RJ~
 

GoldDigger

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That pyrophoric carbonization has been witnessed w/o power in a dwelling by fire forensic engineers elevates the phenomenon past the old staple theory.

But this is less than the magic it appears, if one considers our (American) grounding system proliferating to the point where Mr Kirchoff's rules come into the equation

~RJ~
Mr. Kirchoff's rules apply even to a one load series circuit, you just don't need to use them for analysis.
But, yes, the service neutral can be elevated from ground enough to cause carbonization even though the service line wires are open.
Simplest example is a duplex with one drop and two meters and an open POCO neutral upstream.. Opening one main leaves both neutrals hot.
(I think I saw the same video you did.). :)
 
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