No aluminum is not bursting into flames from the surges. Actually its the normal current that can cause sparks... eventually. Aluminum creeps more than copper. It has an expansion coefficient about 50% greater than copper, so turning an AL wired circuit on and off expands and constracts the wire 50% or more than a copper wire, which can more easily loosen connection screws. That can cause sparking across any developing gap. Aluminum does not conduct electricity quite as well as CU, so it gets slightly hotter than CU, and expanding even more, though they carry the the same amperage. 12 gauge AL wire must be used where 14 gauge CU wire works. If the gauge substitution is not made, AL wire will reach even higher temperatures. AL wiring can go wrong in several ways without actually getting tasered.
Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.
In a brochure aimed at customers in other European countries, the company cautions that the polyethylene Reynobond should not be used in buildings taller than 10 meters, or about 33 feet, consistent with regulations in the United States and elsewhere. “Fire is a key issue when it comes to buildings,” the brochure explains. “Especially when it comes to facades and roofs, the fire can spread extremely rapidly.”
I would be concerned about using that product in any building, irrespective of height.
The biggest problem in aluminum wire is that aluminum oxide that forms almost instantaneously is not conductive, unlike oxides of copper. As a result when the connection cools, the exposed area becomes less conductive, forcing the current to a smaller section. This increases the resistance at that one spot and increases the heat which leads to either direct ignition or melting of the insulation leading to high-resistance shorts to the electrical box which starts a fire.
I expect that the lower thermal conductivity of aluminum decreases it's ability to limit localized heating.
The means to avoid this is to protect the connection from corrosion.
This is from personal experience - one with the pole-wiring that burned up the connection to the house because no anti-oxidant was applied, leading to sporadic power loss to the house. The other was finding 4 inches of bare wire in an outlet box from the insulation that melted back.
Creep, lower section conductivity, higher coefficient of expansion are all contributors, but rapid, low-conductive corrosion of aluminum is the main killer.
Some things have been changed in the wiring industry to offset these effects but, personal opinion, aluminum in home wiring represents a really bad idea, no matter the up-front cost savings.
Excerpt from the Grenfell Action Group blog,
...reports made by residents that they saw and smelt smoke coming from various electrical appliances on the morning of 29th May. This was the day the whole electrical system went into meltdown, and by the TMO’s own admission, fused several key meters and damaged or destroyed electrical appliances in 40 individual residences.
The official count was 45 residences on the upper stories of the building. Residence also reported smoke coming from light fixtures. The Council accepted KC-TMO's response that it wasn't smoke but "steam" from moisture. I am of course speculating that negligence by KC-TMO in dealing with the power surges that went on for 3 weeks in May of 2013, prior to a catastrophic outage and the resulting outage may have damages wiring elsewhere in the structure.
epoxybot just threw another 'fly in the ointment' with the inclusion of significant electrical issues, possibly caused by a faulty building electrical system or a faulty building electrical supply. With the spectre of aluminum wiring also a possibility. Ontario Hydro had quite an issue with aluminum wiring a few decades back.
Added: I qualified the refrigerator issue subject to the manufacturer being aware of a problem.
From the AP, "LONDON -- Britain's government said local officials across the country Sunday should urgently submit samples of exterior panels from apartment towers after authorities found that all samples tested so far have failed fire safety standards."
Problem could be 'really' big... just the tip of the proverbial iceberg.
The 100% failure rate to date (out of 60+ tests) is just jaw-dropping.
I'd like to think that the people who deep-down already knew they'd got a problem got their samples in fastest and that as this next week develops we'll start to see an increasing proportion of passes - but somehow I'm just not that optimistic.
"They should be testing the panels as installed, not just the panels in isolation."
They are testing the panels already installed and these are failing. They should never have used the material, as they are finding out after costing 80 lives.
Whoever specified the material in the first place should be the first on the block... ie, chopping block. It surprises me that there is no mention of lawyers... maybe a different culture...
On BBC Radio 4 this morning they were discussing the fire safety tests on the cladding and the 100% failure rate. It seems that the test regime that has been applied has not been disclosed so it is difficult to say how valid the tests are.
Jed Clampett, - great link, worked ok for me and it's sometimes the way that an outside party can take a better overall look at things than people closer to the action.
Regulations and codes are normally written with the best of intents and purpose to prevent such tragedies like Grenfell Tower. Over time though they can become outdated, not keep track with newer materials and construction techniques and can be applied very rigidly, leading to legitimate calls for replacement, revision or removal. You can get, like this instance, where a desire to do something better for all (reduction of emmissions and increase in comfort due to adding insulation to the outside of buildings, retrofitting gas supplies) comes up against the potential downside of fire up the outside of a building for which it wasn't designed.
The issue here will be that this issue of cladding was highlighted some years ago and for reasons not clear to me, the revision to the building regulations has now been outstanding for some years. The fact that this material is only very marginally cheaper than the "fire resistant" material makes it even worse.
The reality of modern engineering and construction techniques is that little by little things are reduced until the point that they fail. Then it usually takes a significant loss of life in a single incident for action to happen. The potential for this is often there and missed as it has "never happened before". Of course it has, but on a much smaller scale.
Fire protection and prevention in high rise tower blocks has always been an issue - the stay put has worked well up to now when concrete buildings could be relied on to not transmit flames vertically between flats. Now? I think anyone in a high rise who sees fire or smoke will be leaving, which could then cause issues with overcrowding on the fire escapes and prevent fire fighters getting access, no one with smoke hoods etc collapsing and blocking the access, never mind the infirm and disabled.
I think a major factor here was simply the time of year - most people would have had the windows on "vent", i.e. angled inwards at the top and hence transmission of flames was made much easier, which would not have happened in the winter. Of course the windows and window frames may have failed at some point, but this seems to have been an easy way in along with the vents from the kitchen vents (see the picture by epoxy bot).
The UK culture on lawsuits etc is, thankfully, still a world away from the US, but the claims will come in time - the defence though will be that it wasn't banned / against the code that existed at the time and had been used in many locations before without an issue.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
A very weak defense, because that is contrary to how codes work. Codes can't possibly ban the infinite number of potentially inflammable materials that are known to man today for use as building claddings, or ban all new ones that might get invented on the morrow. Codes might list approved materials, but I think it doubtful that there are any materials that have actually been banned anywhere in that code. Are there any materials actually listed as banned? Dry straw used to be a common insulative material, but I would bet it is still not specifically banned by name in the code.
Neither excuses are a defense. Use elsewhere is not exactly a qualification for use, esp in a different location, under different circumstances. As already seen above, it is possible to safely use materials under some circumstances, which may be wholely unsafe under others.
I am afraid that the designer-specifier or accepting agent would bare prime responsibility for not knowing under which circumstances the specified materials could be legally and safely used, unless the materials were specified and accepted for use under false pretense of some sort.
Richard Feynman's Problem Solving Algorithm
1. Write down the problem.
2. Think very hard.
3. Write down the answer.
Question: Would have a non-flamable cladding, installed above a flamable insulation have made a difference? I think not, the cladding would still generate the chimney. Am I wrong?
AFAIK some styrodur insulation are flamable but extinguish when no other fuel is present, then the material of the cladding would be very relevant. Maybe I missed among all the talk about the cladding what kind of insulation was used.
Another question: upthread, and in the NYT article, positive pressure emergency stairways where mentioned. The doors have to open inward, against the pressure. I'd think that maintaining a positive pressure uniformly along the length of a stairwell without the pressure diff locally beeing to high for some people. Likely a solved problem, how is it done?
I think the problem was the thicker layer of insulation applied to the building with an air gap between it and the aluminum encapsulated insulation... This was the cause of the fire spreading so rapidly... the air gap provided a stack for the flame to quickly progress upwards.
From the Guardian, "The government appears to be blaming councils and housing associations for the slow pace of fire safety tests on high-rise buildings after only a tenth of the 600 tower blocks potentially at risk have been tested in the aftermath of the Grenfell Tower blaze.
Theresa May outlined an emergency inspection programme last week that could test 100 samples a day. However, test results have been revealed for only 60 high-rise buildings in 25 areas, and all of them failed combustibility checks.
On Monday, housing minister Alok Sharma said “round the clock” testing was under way, but he appeared to blame landlords for failing to submit samples. "
I can see this being a huge financial undertaking for the councils.
One politician is referring to the negligence as 'murder'.
So the original outreach presentation, by Studio E Architects to residents, included two cladding materials VMZ - Zinc/FR-PE Composite & Marley Eternit - EQUITONE fibre cement facade panels.
An interesting factoid is the Limiting Oxygen Index (%) of a given material. The Limiting Oxygen Index (OI) is a convenient test to make preliminary determinations about the flammability of a given material. It is the amount of Oxygen needed to self-sustain a flame. Atmospheric Oxygen at sea level is 21%. I have read values of 23% & 28% as the value needed to render a material non-flame self-supporting. Paraffin has an Oxygen Index of 16% & Polyethylene (PE) an OI of 17.4%. Most of the data on Polyisocyanurate (PIR) is behind "pay-walls" but the most common IO reference I found was 22-23% and one as high as 29%. With such a minimal need for Oxygen, one would think that PE would burn like a candle but its vapor pressure limits its combustion. A caveat of the Limiting Oxygen Index test is that the flame is applied to the sample from above and the buoyancy of the flame, limits the ability of the test to yield real world results. Many of the most fire resistant materials drop by as much as half the OI% when the flame is applied to the bottom of the sample. This is not true of Polyethylene, it remains at 17%. So one can conclude that the vapor pressure of Polyethylene doesn't make it the best combustible material but its low requirement for atmospheric Oxygen makes it a great fire starter. How good a fire starter is Polyethylene? It has a heat of combustion just shy of diesel fuel. Heat of Combustion in MJ/kg: Paraffin 42-46 / Polyethylene 44 / Diesel 44-45.
A likely scenario is that the burning of the Polyethylene creates a heat column sufficient to render any fire resistance that might have existed in the PIR insignificant. Even though much of the Polyethylene melted, the melted PE would have pooled on the firestop blocking between floors. Molten Polyethylene retains a remarkable amount of heat and would have radiated that heat back up the void creating a flash-over condition & compromising the PIR very quickly. At about 900C the vapor pressure of Polyethylene has no deterrent effect on its combustion and it burns like a paraffin candle, completely leaving zero waste product.
Regardless of the materials that turned Grenfell Tower into a candle, the question should be asked; "Who started the fire?" and considering the very serious electric problems Grenfell Tower experienced in May 2013, the wiring of the building in the undamaged flats needs to be given a thorough forensic inspection and the purchase orders of the electrical contractor examined to determine what remedial measures were taken. In the UK, electrical wiring is typically installed on a 32 amp Ring Circuit and electronics & appliances are protected by fused wall plugs. A refrigerator would have had a 13amp wall plug but they don't blow until they exceed 20amps. If you share your ring circuit with your neighbors (all the units had in-flat prepaid-meters) you can experience a power surge when something like the washing machine of refrigerator draws a high current when the motor starts. And then, their are the tenants of a building who had experienced so many power surges & brown outs; changed out so many fuses on their electronics & appliances. Many who came from undeveloped & developing countries are used to coming up with work-around solution that compromise safety, like hot wiring the fuse holder.
It was intended to work based on a compartmentalized fire scenario, possibly affecting at most two floors. Considering the fire reached the top of the structure in a matter of minutes, one has to question is the intakes of the ventilation system may have sucked & blown smoke into the stairwell.
I have read at least one news item where the Fire investigators are looking into the possibility that the cladding ventilation gap on the columns may have been greater than that on the spandrel 'cassette panels'. My own eye perception last week was that the cladding ventilation gap on the columns appeared to be the width of a 2x4, so 90mm.
MartinLe - people often open doors against positive pressure. This happens when wind is directed against the face of the building the door is in. It takes very little pressure to alter the direction smoke takes.
While there is some risk of some people being unable to push the stairwell door open, there is a far greater risk if smoke enters the stairwell.
epoxybot - although the columns do appear to have been insulated as you can see evidence on the photos I wonder if the deep corrugations on the column allowed flames / air to pass up the inside of the insulation or whether the insulation in those sections was not as thick. Clearly any fire stops on the columns were useless if indeed fitted and long vertical sections appear to be the clear accelerating element.
Remember - More details = better answers
Also: If you get a response it's polite to respond to it.
LittleInch (Petroleum) - I think the trapezoidal relief feature proved to be a difficult surface for the workers to mechanically secure the insulation to the columns. The insulation charred much like what remains on the spandrel panels but the longer sections of charred column insulation fell to the ground during the fire. The trapezoidal area is about 25% of the surface area of the column face and if char formed on the back side and resulted in some expansion, then it pushed the insulation panels away from the column increasing the air gap & fire until the char collapsed. Here is a good photo of the cladding assembly & the fire stop blocking. On the columns, it looks like the fire stop is all that secures the insulation in place. The horizontal presentation of the spandrel insulation, confinement top & bottom plus the fire stop seem to be what held the spandrel insulation in place, for the most part.
