Post-Grenfell Tower Block Safety

This is a set of notes on the Grenell fire written from my point of view as a scientist.  Grenfell was not the first fire of its kind - nor, I am afraid, likely to be the last.  The "lessons learned" from Grenfell may reduce some risks - but they introduce others.  In some respects the scene for the next tragedy is already being set.  There are alternatives, but the "closed mind" mentality of decision-makers leaves little room for optimism that they will ever be implemented.

Eddy Hunt,BSc. MSc. PhD.
See My Objectives

If the need for an alternative to "stay put" and "evacuation by Fire Brigade" is obvious then you may wish to jump directly to <Alternatives>.


On the night of 14 June 2017 a 24-storey tower block in West London caught fire.  The fire spread quickly to the cladding on the outside of the building engulfing the entire building in flames and smoke.  In the end 72 people (about 24% of those present died that night).

I would like to express my sympathies to those who suffered injury and relatives and friends of those who died.  As someone who was personally completely unaffected, I hope that they will accept that the best I can make of this tragedy is to do what I can (especially with my scientific knowledge) to reduce the likelihood that anything like this will happen again.  I would also like to pay tribute to members of the London Fire Brigade who under horrendous conditions and at considerable risk to themselves managed to get some residents to safety that night.

An inquiry was held into the fire, led by Sir Martin Moore-Bick. In October 2017 a "Phase 1 Report" (which I will simply call "the report") was published.  A second report "Phase 2" into the materials and construction methods will be published in the future.

Offering Residents a choice of how to die

Stay put or run for your life - what a choice!  Before Grenfell so-called "compartmentation" was expected to provide residents with safety until they could be led outside by the fire brigade.  That plan went up in smoke (literally) the night of the fire.  The Fire Brigade is now expected to organise the evacuation of tower blocks (of which at least 400 have cladding similar to Grenfell).  Given the obstacles

 - height beyond the reach of ladders
 - almost certain presence of thick smoke
 - possible presence of extremely toxic gases (particularly hydrogen cyanide)
 - long distances up and down challenge the limits of breathing apparatus
 - a single narrow staircase for both rescuers and escaping residents
 - problems of communicating with residents
 - residents with special needs (limited or no English, physical or mental handicaps)

and, of course, no extra legal powers and no extra resources.  How does a service which was clearly overwhelmed on the night "unoverwhelm" itself in the future?

Before Grenfell

The watchword was "compartmentation".  Tower blocks were divided into separate spaces with protection from the spread of fire from one compartment to the next.  Residents calling 999 would be told to remain in their flat provided it was free of fire and smoke.  Details would be taken as to location and number of persons.  The fire service would arrive and have a ready list of places to go.

So-called "stay put" had a number of advantages:

- the fireproofing offered safety
- the fire brigade would have a clear picture of the problem on arrival
- emergency telephone operators could provide assurance and avoid panic

Consider the alternative:
- unknown numbers of people could be wandering anywhere with now way of communicating with them
- they could come up against smoke or other obstacles and become lost
- people could become overwhelmed by smoke or toxic gases
- people could find staircases blocked and begin walking upward - running into those going down
- general panic could break out
- people getting trampled or crushed to death

Before rushing to condemn the reluctance of to cancel "stay put" the above consequences should be carefully considered.

Ever more Dangerous Designs

With the security of "compartmentation" and no doubt under the pressure to reduce construction changes were made to the designs to large blocks of flats - particularly but not exclusively those intended to house council tenants.

I listed the main steps in this process - along with a brief indication of what I believe should happen now in an email sent jointly to the "Grenfell United" group of former residents and the Fire Brigade Union - see <No Second Grenfell>>"Wno2ndGT"

The night of the Fire

The events of the night were covered in detail in Phase 1 of the report.  An electrical fire broke out in a first floor flat and at 56 minutes past midnight the resident called 999 (the UK emergency telephone number).  For simplicity and clarity regarding the speed of events I will use this moment as the starting time for the events which followed.

+5 minutes: first firefighters arrive at the tower
+15 minutes: firefighters enter the flat and observe that the fire has begun to spread to the cladding
+30 minutes: first 999 call from another flat (22nd floor)
+31 minutes: first report of smoke entering a flat (14th floor)

(From this point the calls begin to multiply.  Normally 999 operators will remain in contact with the caller until help arrives - but there are more calls than handlers.  The usual calls from minor fires and false alarms are also coming into the same centre.)

+37 minutes: 110 persons have escaped (out of 297 in the building that night)
+56 minutes: 168 have escaped
+1hr26 mins: smoke in "many of the lobbies"
+1hr53minutes: "stay put" is cancelled - call handlers are now advising callers to make their own escape

(at this point it appears that one face of the building is still intact)

+1hr56 mins: "less smoke in the stairs than in the lobbies"
next morning: one final survivor leaves the building

The report is highly critical of the failure to revoke "stay put" stating that the casualty numbers would probably have been less.  This appears to be supported by the numbers escaping.

Could the fire brigade have seen this "window of opportunity" on the night?  These things are always clearer with hindsight than at the time.

Follow the laws of Physics

Everyone (especially the fire brigade) was astounded at the speed with which the fire spread.  When diagrams were published in newspapers and applying my knowledge of physics I could see immediately factors which would permit the fire to spread up the side of the building.

Fire is an exothermic chemical reaction.  ("Exothermic" means that it gives out heat.)  There are three things which are needed to sustain fire:

- a high temperature
- fuel to burn
- a source of oxygen (air is 20% oxygen)

Essentially it is a "run away" reaction.  The heat from the fire keeps the temperature high. So long as there are things to burn and a supply of fresh air the fire will continue burning.  The design of the cladding on Grenfell tower ensured that fuel and air were plentiful.

The fire began as a small single flat fire.  Provided the flat can be sealed off the fire will be limited by the air in the flat.  Somehow, however, the fire spread to the cladding outside. This occurred probably because the window frames were made of uPVC which melts at a relatively low temperature.  Once air can get in through the gaps (the wind may have been a significant factor) then the fire in the flat will increase in intensity and spread to the outside.

Once outside the flat the fire will come into contact with the ACM cladding.  This consists of highly combustible material (polyethylene) surrounded by aluminium.  The flames are likely to melt the aluminium, exposing the polyethylene, which will catch fire.

The gap between the cladding and the concrete wall of the building provided the opportunity for a "chimney effect".  The hot air moves upward to be replaced by cold air (which brings a fresh supply of oxygen) from below.  This means a continuous current of air to sustain the fire. It is likely that burning bits of polyethylene will be carried upward and the cycle will repeat itself at higher levels in the building.

Another effect which will probably occur is that the glass in the windows will become hotter on the outside than on the inside.  This will create thermal stress.  Under such circumstances, glass will shatter. The windows are now gaping holes and the prevailing wind will bring in continuous fresh supplies of air.  There is nothing now to stop everything in the building from burning.

Combustion is unlikely to be complete everywhere and the air will become filled with small particles of carbon - i.e. thick black smoke.  This makes it difficult for anyone caught up in the fire to breathe or find their way about.  A further danger of incomplete combustion is carbon monoxide.  This will hinder breathing and eventually lead to unconsciousness and (unless someone carries you out) death.

A further danger with cladding identical to that used in Grenfell is cyanide poisoning (see below).

Considering the above, it is probably better to as "Why did so many people escape?" rather than "Why did so many people die?"  One phenomenon appears to be that the smoke was far less intense in the stairwell than elsewhere in the building. Of course, that cannot be guaranteed to be the case in another fire.

Don't ignore the Cyanide

One of the materials used in the cladding in Grenfell was an insulator called "polyisocyanurate".  It is sold as a "flame retardant" because it is less combustible than polyethylene.  In this material the polymer chains are connected via a six-atom nitrogen and carbon ring.

As temperatures rise, the bonds linking the atoms begin to break - with the weakest bonds breaking first, leaving the 6-member nitrogen-carbon ring.  At higher temperatures the ring will break leaving a chain of 3 pairs carbon and nitrogen atoms.  The carbon-nitrogen bond is a very strong bond and eventually you will have three ions of one carbon and one nitrogen.  This ion is called "cyanide".  It is one of the most potent poisons known.  Walking just a few paces through a cyanide cloud will cause you to become incapacitated and die quickly.  This is particularly dangerous because an apparently clear escape route can be a death trap.

Several people were treated for exposure to cyanide after the Grenfell tower.  It cannot be excluded that many of the dead may have died from cyanide poisoning.

Immediately following the fire some newspaper reports mentioned cyanide.  The Report, however, appears to make no mention of it.  (I have read the summary which is highly critical of the decision to offer "stay put" advice so long after the fire started.  The possible presence of cyanide is highly significant here because it could lead to mass mortality in the stairwells.  The worst way to react to a source of danger is ignore it  - or even deny its existence.

I am personally astounded that a cyanide-emitting material is being used (apparently in full legality) as an insulation material.  In the discussion that followed Grenfell there has been concentration on building regulations.  Did the cladding contravene building regulations? Do the regulations need to be changed?  Was the polyisocyanurate tested for the gases it emits or just for flame resistance?  The amount of paperwork multiplies.  In the mass of detail obvious questions disappear from view.  In any situation there will always be someone to say "We comply with all regulations".  Who makes the regulations?  Governments usually turn to industry for advice - and they in turn have their own financial interests in mind when they give that advice.

From a scientist's point of view the picture is simple.  Once a fire starts the building regulations will not make the slightest difference to how the fire develops.  The laws of physics permit good predictions regarding the danger of fire. Those who are ignorant of the laws of physics should not be designing buildings.  Those who knowingly endanger the lives of others should be required to respond to exactly that - and not for some oversight or error in interpreting some regulation.

"Wait for the Report"

After the fire the Government responded with steadfast determination to do nothing in the short term to improve tower block safety.

They ordered two reports - one to look into fire regulations and the second to look into the fire itself and the construction methods.

At this time I wrote (via my reluctant MP) to the Housing Minister with an explanation from scientific point of view of how the fire could have spread so rapidly and caused so many fatalities.  I included a suggestion for six things which could be done very quickly and at low cost to reduce the danger.  The Minister's reply went to lengths to avoid acknowledging the existence of the suggestions.  Was I the only person in Britain who offered suggestions?  All I can say for certain is that the Minister had a least one list of possible actions.  (I mentioned my scientific qualifications and experience and I presume that government ministers have access to scientific advice - hence there should be no excuse for simply disregarding the letter.)  This is what I mean by "steadfast determination to do nothing".

The minister mentioned the two reports - so from his point of view the matter was "in hand".  Now, over two and a half years later, and with some 400 similar tower blocks still inhabited there has still be no fundamental change.  Fairly generic advice has been given - firefighters need to be "better trained", communications must be improved, fire inspections need to be carried out -but how do put a safety certificate on a building which is a death trap by design?

Following the Grenfell fire residents will be much more inclined to evacuate themselves in the event of a fire.  This will mean that people could be anywhere in the building, possibly lost and encountering smoke and other obstacles and with no systematic system for communication.  How will the reformed "better trained" crews deal with this situation?

Two and a half yeas on it seems to me that tower block residents are in as much danger as ever.

Despite the seemingly formidable obstacles, I believe that I believe that with planning and the active involvement of tower block residents, they can be made quite safe - see <Alternatives>.

MPs say "sprinklers

The Grenfell fire became a matter for discussion in the House of Commons.  Here it ran into an often repeated confrontation between the two main parties - Conservative (the Government) and Labour (the main opposition party).  The two parties have very different reflexes when it comes to dealing with these matters.

The Labour Party seek a highly visible solution to the problem and as a demonstration of their commitment to the solution they are prepared to borrow vast sums in order to implement that solution.

The Conservative Party, on the other hand, constantly complain about the deficits that they have inherited from Labour and warn of the dangers of overspending.

The solution proposed by Labour was to "retro fit" sprinklers.  Sprinkler systems which automatically release water in response to a fire are best fitted at the time the building is put up.  They can be fitted later but at considerably greater expense.

What difference would sprinklers have made to the Grenfell fire.  It is possible that they could have put out the fire before it spread beyond the flat where it started.

But some caution is needed.  The vast majority of fires in tower block flats are electrical in origin and water fire extinguishers are not recommended for electrical fires because water is a partial conductor of electricity and may cause short circuits in electrical equipment.  Also if water gets onto the staircase then it could cause people to slip and fall on stairs.  Even a single person breaking a hip on stairs could present a significant obstacle to evacuation.

In conclusion, sprinklers may reduce the risk but a complete solution they are not.  And the money has to be found from somewhere.


But how do you get them all out?

One of the more memorable exchanges of the Investigation - the chair demanding plans for evacuation and the fire brigade chief admitting that they had not found a solution.  There is no evident solution given the magnitude of the problems described above.

I believe that both sides of this disagreement have a blinkered view of the situation.  The choice limited to "stay put" on the one hand and the fire brigade arriving at a tower block on fire, and proceeding extract the residents on the other hand, is a false one.  The situation calls for alternatives beyond the imagination of either of these two people.

One thing is certain - and that is that "stay put" will be of limited value in the future.  After the experience of Grenfell most residents will begin to evacuate themselves.

When people begin to self evacuate they must negotiate up to 24 floors of potential obstacles. If they get blocked there is no alternative to either continuing past the obstacle (this could involve climbing over bodies) or going back to their flats and calling 999.

What is urgently needed is places of safety along the route.  I have called these places "refuge flats".

These meet two very important objectives:

1. the further down residents can move, the easier it will be for the fire brigade to rescue them
2. the more residents gather together in groups the easier it will be to communicate with them.

Refuge Flats

Refuge flats would be flats made available to escaping residents at regular points along the single escape route (i.e. the single stairwell in most tower blocks).  There are numerous unanswered questions in this brief description.

- Would anyone live in a refuge flat?
- Would they be equipped differently to other flats?
- How do you avoid toxic gases along the escape route?
- How do you prevent people from becoming lost?
- What about the evacuation of people with disabilities or limited English?

I believe that there are potential answers to all of these issues.  But it does involve a fundamental rethink - see <Rescue Flats - a possible implementation>.

Throughout the above discussion I am not pretending that I have all the answers and other people  have none.  What I am saying is that there alternatives that need to be considered.

At present we are drifting into the future with no fundamental rethink, effectively waiting for another Grenfell type of disaster to happen again.

That is what I am trying to avoid.

Eddy Hunt, BSc,MSc,PhD