Why Grenfell Tower became a raging wind tunnel of a fire

"It had to be a cladding fire."

British fire protection specialist Arnold Tarling isn't wondering what caused the fire to spread so quickly in London's Grenfell Tower early Wednesday. He's certain the recently added exterior cladding system is to blame.

For years, the associate director of London-based Hindwoods Chartered Surveyors has been calling for improved fire safety regulations in the country.

Tarling said he burst into tears when he first heard from a fellow fire expert that the highrise was on fire.

Following is an edited transcript of an interview with him Thursday by CBC executive producer Tracy Seeley.

Q: In your opinion, what happened?

There was an initial source of fire. That cause is entirely irrelevant to what happened later. What happened is the fire got out of a flat, maybe from an open window or through a broken window from the heat. And then it started heating the panelling and the insulation above. That then set a chain reaction in which the panel started to burn.

The panels being aluminium, melt at 600 degrees [Celsius] or thereabouts. But the fire brigade cannot put out any of the fires behind these panels, because there's metal there. You also have a wind tunnel effect sucking the flames up the wind tunnel, up between the insulation and the external cladding, melting the solid polyethylene above, and continuing the fire right up the height of the building."

The cladding system is combined polyaluminum sheets with a filler of polyethylene. And that is what has caused the problems, because the polyethylene melts at a very low temperature and it catches fire. It is basically like a candle which is sandwiched between two sheets of metal.

We have seen those fires before. There was one in 2014 in Melbourne, Australia, but those didn't enter the flats, because I understand the flats were sprinklered. In Britain, we didn't have these flats sprinklered, and therefore the fire was able to enter the flats quite rapidly.

Q: What does this say about these modern methods of construction that could be potentially so dangerous?

What it actually says is that the building regulations we have in this country are not fit for this form of cladding. All that you require to meet the standards is that the outside surface shouldn't allow the spread of flames. What is going on behind the metal or the other surface is entirely irrelevant to building regulations. You could put expanded polystyrene in there, or anything else that burns.

Q: The construction company has said it followed regulations.

I have seen nothing yet that the architect or the contractor or the supply of materials breached the building regulations. The horrendous fact is that in 2014 I did a talk to the British Standard Institute at one of their fire conferences. And I said this will happen in this country. There will be multiple fatalities as a result if these cladding systems are not changed.

Q: How do you feel?

To be honest I burst into tears. This tragedy is totally avoidable. I would say it is wicked that these people have had to die. When I got a phone call from another expert at quarter to four in the morning, I went downstairs turned on the television and burst into tears. My wife came down thinking my mother had died.

It is terrible what has happened. It needn't have happened. And the people responsible are either the politicians or their advisers. It need never have happened.

Q: What do you expect will happen?

Well, on the scale of what has happened in previous years where we've had inquests where it has been said we should have sprinklers in respective buildings and fitted retrospectively, what do I expect of government? Nothing! Nothing's been done. Nothing's been acted upon.

Time and again they said lessons will be learned. If I hear another politician say lessons will be learnt, I will scream. It is just soundbites. It's just meaningless, just saying lessons will be learned when they've never been learned from the past.