Grenfell Tower Fire: Questions & Answers

By Frances Maria Peacock MCIAT, IHBC, MIFireE, MSFPE, PG Cert., BSc, Dip. HE

On 14 June 2017 a tragic fire occurred at Grenfell Tower in London which claimed 72 lives.  The building had recently undergone a refurbishment which had involved the installation of a rainscreen cladding system on the exterior of the building.  A small fire which began in the kitchen of a fourth-floor flat was able to ignite the cladding on the outside of the building and result in a severe fire which involved most of the building.  Once alight, the fire spread rapidly  across the façade from which it was able to enter the flats via the windows.  Many occupants were able to get out, but others were trapped in their flats and sadly did not survive.

Below are a series of questions I was asked during an interview and the answers I gave.  They provide an insight into what happened, what went wrong and what needs to be done to prevent a repeat of the disaster.

What type of Building was Grenfell Tower?

A high-rise brutalist concrete tower block which when built had twenty floors and a total of 120 flats.  It was designed in the late 1960s, construction began in 1972 and the building was completed in 1974.

Explain the basic components of the building:

A reinforced concrete frame comprising columns, beams and slabs around a concrete core.  These tie the building together.  The whole structure sits on a deep foundation of 2m of solid concrete below a 4m basement.  The lifts, stairs, dry riser and services are in the building’s core.  The tower was designed to be robust and resist collapse, bearing in mind that the Ronan Point disaster occurred in 1968 whilst Grenfell was being designed.

What type of fire considerations does one need to make when making a building of this nature fire safe?

Compartmentation is very important.  Each flat should be a fire-proof compartment in its own right, thus able to contain a fire and prevent it from spreading to the rest of the building.  The walls should be able to provide at least 60 minutes fire protection, which should be sufficient to allow a fire to be extinguished, or people to evacuate if that is deemed necessary.

Openings such as windows, doors, vents and service penetrations should be protected with cavity barriers or fire stops.  The use of non-combustible building materials, adequate means of escape (eg. Protected stair), fire mitigation measures (eg. Sprinklers), firefighting facilities and protection measures (eg. Fire resisting doors) are all important.

What were fire safety standards for buildings like at the time of construction, historically speaking?

The standards to which the tower was constructed were those which applied to London in the early 1970s.  These were the London Building Acts of 1930-39 and associated by-laws.  Grenfell Tower was constructed under the British Standard Code of Practice 1971 and Section 20 of the 1939 Building Act which sets out requirements for fire safety.  In 1985, London was brought under the same system as the rest of England and Wales, following the Building Act 1984 and the Building Regulations of 2010 which are governed by it.  The regulations do not contain prescriptive technical requirements, only functional requirements which must be met (eg. Walls adequately resisting the spread of fire).  Guidance as to how to comply with the regulations is set out in Approved Document B 2006, although there is no obligation to follow the guidance and one may instead comply with the functional requirements by some other means.  There is a greater level of flexibility in the new regulations.  The older ones were more rigid.

What were the biggest points of weakness (in terms of fire safety) in any high-rise residential building?

From a firefighter’s point of view, being able to fight the fire safely and effectively.  Entering or ventilating apartments without making the fire worse and putting themselves and others at risk can be a problem.  The spread of smoke and heat is also another weakness, because once doors start being opened, it is difficult to contain this.  There can also be problems with water pressure in the riser at high levels in a building.  Evacuation is another issue; who do you evacuate and when, or should residents stay put?  Smoke extraction systems and fire alarms can be weaknesses, especially if they don’t work as intended.  There was even one case where a fire spread via a smoke extraction system.  There is also plenty of opportunity for the spread of fire in ways which can be unexpected, and by less obvious means.

Was the original Grenfell Tower a “safe” building?

Yes, it was a very safe building.  There had been previous fires in the tower which had not spread beyond the compartment of origin.  The external cladding added during the refurbishment changed this because it provided a means for the fire to spread externally and enter other flats, thus breaching the compartmentation.

When were refurbishments carried out and what was changed or added?

The refurbishment of the building was completed in 2016 and was signed off on 7 July.  The work involved fitting a rainscreen cladding system to the exterior of the building, a new crown, replacement windows and alterations to the lower part of the tower to add nine extra flats.  There was also new gas piping and the replacement boilers put into the flats.  In 2011 new front doors had been put on the flats, which were supposed to have 30 minutes of fire protection.

What effect did the refurbishments have on the building?

The cladding, to put it simply, turned the building into a fire hazard.  Many of the residents had issues with the cladding; some complained that it rattled.  The windows are reported to have had several issues including gaps under the cills and draughts coming in around gaps around the edges of the windows.  The fire resisting doors in reality only offered fifteen minutes protection and were not able to cope with flashover conditions.  Many also lacked self-closing devices, thus contributing to the spread of smoke within the building on the night of the fire.

Were the refurbishments carried out typical of refurbishments at the time/in a modern building?

A lot of high-rise buildings have had replacement windows and cladding systems fitted to the external façade.  This was unfortunately fairly typical for the time and is a reason why there are hundreds of buildings across the country which have flammable cladding which requires removal in order to make them safe.  The combustible nature of certain cladding and insulation products was known prior to Grenfell, but the risk was considered low if other fire protection measures were in place.  This however was not a view I held.

Where did the fire originate?

In the kitchen of Flat 16 on the 4th floor of the tower.  Flat 16 is in the NE corner of the building.  Evidence suggests that the fire started in a large fridge-freezer at the SE end of the kitchen.  The evidence which supports this is as follows:

The occupants of the flat stated that the fridge was on fire;

The firefighters which entered the flat in the initial stages of the fire saw a fire involving the fridge-freezer;

Investigators found a burn mark on the floor underneath the fridge-freezer, whilst the floor on either side was undamaged.  The skirting board behind the appliance had also been destroyed, indicating a greater source of heat in this location;

An examination of the consumer unit by an electrical expert found that the circuit breaker for the kitchen had tripped.

How did the fire reach the cladding?

My initial thoughts at the time of the fire were that the window jambs must not have been adequately protected against the ingress of fire, and therefore the fire was able to find its way into the interior of the cladding system.  The exact point of entry has never be determined with certainty, but the window jambs are considered the most likely point of entry.  The replacement windows were inserted forward of the originals so that they were within the thermal envelope of the building (cladding system), rather than the concrete frame.  There were no cavity barriers around the windows (there should have been), and the cavity was closed with combustible material (a uPVC window surround behind which there was an EDPM membrane).  Other possible points of entry are the head and cills of the window – at which there were gaps – and through the window itself which was believed to have been open at the time.  Another possibility is the extractor fan on the window, as has been shown in subsequent testing, although it is too soon to draw any firm conclusions yet.  It is also possible that there were several points of entry.

Can you give a sense of the fire’s journey and its speed?

The fire spread up the east face of the building very rapidly after the cladding ignited.  In only 20 minutes it had reached the top of the tower from the fourth floor.

What factors contributed to the spread of the fire?

Greater details are given elsewhere but first and foremost, the main factor is the combustible nature of the cladding panels, as well as other flammable materials present in the building such as PIR insulation.  The second most important factor is the shape and geometric profile of the building.  If this was different, then the fire spread would have been different and it may not have been as extensive.

Can you describe the cladding system – its elements and materials used?

160mm (consisting of 2 x 80mm boards) of PIR insulation, a ventilation cavity of 156mm and aluminium composite panels of 4mm thickness (3mm polyethylene core sandwiched between two aluminium skins, each 0.5mm).  On the columns, the width of the insulation was 100mm and the ventilation cavity 142mm.  The panels were hooked onto aluminium support rails, which gave a better appearance because no fixings such as screws or rivets could be seen from the outside.

What was the purpose of the cladding?

The cladding had two fundamental purposes; to insulate the building so that it would be thermally efficient, and to modernise and improve its appearance.

What are thermoplastics?

Hydrocarbon based products with good thermal properties, able to keep a building warm in winter and cool in summer.  Unfortunately because they are essentially oil based, they are highly flammable.  An example is polyethylene which formed the core of the cladding panels.

How did their use contribute to the fire spread?

The polyethylene (PE) cores of the aluminium composite panels (ACM) and polyisocyanurate (PIR) insulation boards have physical and chemical properties which encourage fire to spread rapidly.

Polyethylene is a material with a low thermal conductivity, which means that heat has a tendency to accumulate at the surface rather than being transferred deeper into the body of the solid by conduction.  This results in a rapid rise in temperature, enabling the material to ignite more easily.  As polyethylene and Polyisocyanurate are both of low density, they heat up rapidly when exposed to a heat transfer process such as radiation.  This is because they have a low specific heat capacity, which means that they will heat up faster than materials with a higher heat capacity because it takes less energy to raise the temperature by a given amount.  The PE cores of the cladding panels have a high heat release rate, which results in a higher rate of combustion, causing extremely rapid fire spread.  The rate at which the heat is released is often of greater significance than the amount of heat which is produced in a fire.

Explain the European Standards for Fire Testing rate materials and where each of the materials used came on that scale compared to what was required (eg. A2 rating required, ACM was the equivalent of Class E):

There are different ways of testing cladding materials and they should always be tested as part of the assembly in which they will be used.  Combinations with other materials can make a difference to the outcome.  The ACM at Grenfell achieved a Class O rating when tested as part of a specific assembly which did not match that at Grenfell.  However, the tests for Class O, also referred to as Class 1, only assess fire propagation and the spread of flames across the surface.  They do not assess combustibility.  When the product was tested for its combustibility using different criteria, it produced results that placed it in Class E.  Euro Classes A1 to F are assessments for combustibility and assess the contribution the product makes to a fire, as well as smoke production and release of droplets when the material melts.

What changes were made to the windows and their proximity to the cladding?

What types of materials were used around the window area?

Some of this has been answered as part of Q11 above.  I shall add to this by saying that the windows were moved forward of their original positions for thermal efficiency.  In other words, by placing the windows within the cladding system rather than the concrete frame, heat loss would be reduced.  The original windows from the 1970s were sliding with aluminium frames set within a wooden jamb.  The new windows had polyester powder coated aluminium frames and were set within a uPVC surround.  Crucially, uPVC will start to soften in temperatures as low as 55°C, and as the temperature starts to rise further, it will deforms allowing flames to penetrate the construction.  Typically, this will be between 70° and 90°C.  By the time the temperature gets to around 100°C, it will have lost its integrity.

Were these material combustible?

UPVC will soften and then burn, giving off harmful fumes.  It does not offer fire resistance, due to its inability to maintain its integrity in the high temperatures reached during a fire (see above).  EPDM, which is a weather-proof membrane is also highly combustible and will not provide resistance against fire.  These materials were used to seal the windows jambs and the latter was used to fill gaps because the windows in many cases did not fit well within the new openings which had been created.  Between each pair of windows was an insulated infill panel which contained extruded polystyrene (XPS).  This will typically shrink when exposed to heat, but will nevertheless give off poisonous fumes and produce droplets of burning material.  However, the contribution of these is considered small.

Are windows generally weak points/fire resistant areas?

Yes they are, as are all openings in the construction including doorways, vents and service inlets.  All must be adequately sealed against fire with materials able to offer adequate fire resistance for the required period.

What is a cavity barrier and what is its purpose?

There are two types of cavity barrier – vertical and horizontal – and there purpose within a rainscreen cladding system is to inhibit the spread of fire through the ventilation cavity.

Vertical cavity barriers – these vertically divide the cladding system into zones and are always in the closed position, being the full width of the cavity and fitting tightly between the masonry wall of the building and the cladding panels at the front .  The idea is for a fire to be contained within a zone between two vertical barriers.

Horizontal cavity barriers – these are installed in the open position with a gap to allow the system to ventilate.  They have an intumescent strip, and heat from a fire will cause them to expand and fill the gap, thus preventing the fire spreading upwards through the cladding system.

Once the barriers are closed, the fire is contained within a box (zone) within the cladding system, as it will then be surrounded by barriers on all sides.

Where are they needed and what happens when they are not there or are not sealed?

Cavity barriers are required around door and window openings, as well as locations where the walls change direction where the protection of corners is important.  They should also be installed at locations in line with compartment walls and floors.  On blank faces of wall, they will be required at intervals to break the system into zones (as explained above) so a fire can be confined within a limited area.  If the barriers are incorrectly installed or are missing – both of these were issues at Grenfell – fire can spread through the system unrestricted.

In some cases, cavity barriers can prove ineffective.  If the cladding panels have combustible cores, as was the case at Grenfell, the fire can spread within the cores of the panels by-passing the cavity barriers.  The panels can also deform, creating a gap between the barrier and the panel, thus allowing fire to spread.

What was the architectural crown?

This is essentially a parapet around the perimeter of the roof of the building.  The original ground was made of concrete beams punctuated with portholes for decoration.  Its purpose was to prevent people from falling over the edge because there was access to the roof via the plant room.  When the building was refurbished, the original crown was left in place and the new crown installed in front of it.  As the original crown had been left in place, the new crown was added for no other reason than aesthetics.

What material was it made up of and how did it contribute to the fire?

The old crown, being made of concrete was non-combustible, but the new crown which was covered with ACM panels was highly combustible.  In other words, a dangerous feature was added to the building just to “improve” its appearance and to give the building a crown which matched the rest of the cladded façade.

The crown had a significant influence upon the fire.  If it was not for the crown, the spread and behaviour of the fire would have been rather different.  The factors which affected the way in which the crown contributed to the fire are: its overall orientation, its design, its type of construction and the fact that it was in an exposed location at the top of the building.

The fire dynamics associated with this are complex and it is necessary to read Chapter 7 in my report for details.  However, a draw of flames through the new crown as it started to disintegrate, as well as a draw of flames between the old and new crowns were factors, as were the flaming droplets and molten material produced, which dripped and flowed down the building causing the downward spread of fire.  Molten material which collected in a gap which opened up at the base of the crown caused a pool fire which helped the fire to spread further.

What is the function of the enclosed stairwell and concrete core?

The concrete core is part of the structural frame of the building and helps tie the building together, as it connects to the reinforced concrete floor slabs which are tied to the beams in columns.  The loads are then transferred through the vertical elements to the foundations.  The other function is to provide a central location for the stairs and lifts to allow a configuration of six flats per floor.  Some blocks have stairs and lifts located at one side or one end, but have fewer flats per floor.  It also provides a convenient location for services and the dry riser, which needs to be within easy reach of all flats.  In some buildings where there has been a fire, the firefighters have had difficulty getting water to the flats furthest from the riser.  The stairs were enclosed with fire resisting doors and should have been protected against fire and smoke, thus allowing safe egress for occupants.

What other internal components of the building failed?

The fire resisting doors on the flats did not provide the required resistance against smoke and flames.  In some cases, doors were left open allowing smoke to spread due to a lack of self-closing devices.  The doors to the stairs performed reasonably well, although smoke and heat were allowed to enter due to doors being opened for access, or otherwise being propped open for firefighting purposes.  The latter is a common issue in blocks of high-rise flats.  The smoke extraction system was also unable to cope with a fire on multiple floors, although they are not generally designed for a fire so extensive that it affects almost the entire building.

What were conditions like inside the tower during the fire (lighting, floor numbering etc.)?

The lighting in the communal corridors was poor, with many residents who evacuated their flats not being able to see where they were going and describing the conditions as pitch black, hot and smoky.  Some had to feel their way towards the door to the stairs, whilst others knew its location and could wander towards it if their flat was in one of the more convenient locations.  Visibility was very poor in places due to the intense smoke.

Some parts of the stair became particularly hot, causing the rails to become too hot to hold and light fittings to melt.  This hampered the escape of some residents.

There was confusion with floor numbering.  Following the refurbishment, the floor numbers changed due to three additional floors being inserted below.  What had been the first floor became the fourth floor, and what had been the twentieth floor became the 23rd floor.  The floors were not clearly numbered, and often residents returning home would go to the wrong floor.  This caused confusion for the fire & rescue service on the night.

Can you describe the smoke and how this was different to smoke in a normal fire?

Smoke is essentially the product of incomplete combustion and its content depends on the type of fuel involved.  It is the smoke which tends to kill people in fires rather than the flames, as the harmful chemical substances it contains cause asphyxiation and poisoning.  At Grenfell, the smoke was hot and choking, and it contained hydrogen cyanide which is a poisonous gas.  The thing which sets Grenfell apart from other fires is the particularly large quantity of toxic smoke which infiltrated most of the building.  Given the large amount of cladding present on a building that size, there was an exceptionally large fire load capable of producing increased amounts of smoke, heavily laden with toxic substances.   Many people who tried to leave their flats returned because the smoke made it impossible to reach the door to the stairs.  They couldn’t breathe and it irritated their eyes.   Some people eventually succeeded after several attempts, placing damp cloths over their mouths and noses, but nevertheless many were still overcome by the particularly noxious fumes and collapsed on the stairs.  Some people even died on the stairs.  Others who were unable to leave their flats due to the smoke eventually perished. 

How was the escape from the stairwell compromised?

By smoke and heat from opened doors, and by the failure of lighting in some places.  Those on the upper floors found it particularly difficult to evacuate this way due to the length of time it took them to get down to the ground, thus exposing them to the heat and toxic smoke for longer.

How did the geometry of the structure possibly contribute to the fire spread?

The first thing that struck me at the time of the fire was that the geometry of the building seemed to be affecting the behaviour of the fire.  I decided to look at the further and undertook some research to see whether the overall shape of a building, its geometric profile (eg. Structural features such as columns and recesses) and architectural features (non-structural features such as string courses and parapets) really did affect the spread and behaviour of fire.  The results – set out in a 173-page report completed in October 2019 – show that geometry has a significant influence and in fact all high-rise building fires which involve a combustible façade are influenced by the geometry of the building.  The fire dynamics are complex, but generally, certain features encourage a fire to spread and enable it to reach parts of the building which it would not otherwise have done so if they had not been present.  At Grenfell, the crown and the columns facilitated the fire spread.  If these had not been present, the fire would not have spread so extensively.  The more complex the geometry of a building, the more extensive and severe a fire is likely to be.  Of course the columns and crown were not dangerous when the tower was first built; they became dangerous after they were covered in combustible cladding.  If the cladding had been applied only to the spandrels, and the columns and crown had been left with their original concrete surfaces, the fire would have been much less extensive.

What was the approach and behaviour of the emergency services that night?

The fire brigade had never dealt with a fire on that scale before and were unprepared.  They arrived at the scene expecting to extinguish a small kitchen fire, but once it took hold in the cladding and were unable to control it, they did not know what to do.  The firefighters had no idea how the fire would spread or behave, and therefore could not plan their firefighting strategy effectively.  They told residents to “stay-put”, but even when it became clear that the compartmentation was being breached, they did not change the advice.  As little as half an hour after the fire started, it was clear that it could not easily be extinguished and that the compartmentation of the flats was being compromised.  This is when stay-put should have been abandoned in my view, and the residents evacuated in a controlled manner.  Instead, the advice was not changed until 02.47, when people were advised to get out if they can.  By then it was already too late for many of the residents.

The other issue concerned the staff in the control room who were remote from the fire ground and gave advice without really being aware of the true situation.  Communication was another issue with information not being passed between various personnel as effectively as it should.

How was this fire different to other fires in high-rise buildings?

To put it simply it was the fact that the fire was able to enter the building at multiple levels whilst most residents were still inside.  There have been many serious cladding fires around the world, but the only other one with a high death toll was in 2010 in Shanghai, when 58 died after scaffolding around the building caught fire and it entered the interior at multiple levels.  That building too was undergoing refurbishment and had ACM cladding.

What are the biggest learning outcomes from an incident like this?

What can be done to prevent another fire with the same loss of life?  Most obviously not use combustible materials on high-rise buildings.  We also need to look at the way in which the construction industry operates, learn lessons and make changes.  Issues with firefighting and evacuation were identified.  We need to learn from these and ensure that the right improvements are made.

What changes have been made as a result of this disaster?

The building regulations have undergone review and the Government has introduced a ban on combustible cladding which came into force in December 2018.  However, this does not include buildings under 18m tall – some of which fall only a few centimetres below – and are without doubt high rise, or buildings such as hotels.  However, the ban has since been reviewed and a threshold of 11m is being considered as well as a widening of the range of buildings covered.  I have participated in these reviews and I welcome these changes.

What changes still need to be made?

Firefighters need better training to deal with high rise fires, and as part of this they need to learn the principles I have developed which relate to how a fire spreads and behaves on the outside of a building with a combustible façade.  My research on the effect of geometry on fire has led to the development of a set of principles from which the spread and behaviour of fire on a façade can be predicted.  We also need better testing of materials and assemblies of multiple products on apparatus which is representative of the buildings upon which they to be installed.  Finally, there are hundreds of buildings around the UK covered in combustible cladding which are still awaiting its removal.  Progress with this is much too slow.

About Frances

Frances Maria Peacock is a Chartered Architectural Technologist and a Fire Engineer.  Since the Grenfell Tower Fire of June 2017, she has been involved in research to examine the relationship between building design and fire spread, and has written several technical papers and reports which have been submitted to the Grenfell Tower Inquiry.  Frances is a member of the Institution of Fire Engineers, the Society of Fire Protection Engineers, the Chartered Institute of Architectural Technologists and the Institute of Historic Building Conservation.  She also has membership of the Royal Institute of British Architects.  Frances is a member of several fire safety task forces and committees, including the Standards Setting Committee of the International Fire Safety Standards Coalition.

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