Grenfell Tower: lessons learnt

By Jock Litterick

Industry expert Jock Litterick looks at what really happened during the Grenfell Tower fire, what should have happened, and what lessons can be learnt from this tragedy.

I ran into an old friend, Jock Litterick, while in Durban and we spent some time catching up. Jock was instrumental in my move from air conditioning to smoke ventilation, and I had not seen him for several years due to medical boarding. During the conversation, the Grenfell Tower fire came up, with Jock’s take on the fire differing from the thoughts I had shared several months ago. Jock explained how he had penned his views on the matter, so I requested his permission to publish these in my RACA Journal column.

Jock is no stranger to the fire consulting community and I thought his view would encourage more discussions around indifferent approaches to compliance and protecting South Africans, hopefully avoiding the horror of another fire.

So here follows Jock’s article …

What happened?

In the early hours of Wednesday, 14 June 2017, fire broke out in the 24-storey Grenfell Tower apartment block. The London Fire Brigade arrived six minutes after the alarm sounded and extinguished the fire within minutes. As the crew was leaving the building,  firefighters outside spotted flames erupting from the exterior of the building.

The original fire had started in a flat’s fridge on the fourth floor. The secondary fire proceeded to kill 71 men, women, and children. The block was built in 1974 and the truth is, a conflagration of such proportions should never have happened.

What should have happened that night?

The official version of what happened that night is still subject to the findings of the official enquiry; however, we can postulate as to what should have happened based on an understanding of passive fire safety measures and simple fire dynamics.

To establish this, we need to look at the original design objectives of the building. On the one hand, this is difficult because we do not have access to the British Building Regulations of 1974. On the other hand, I have personal experience of Scottish 1960s high-rise design: I had moved into a new 19-storey block in Glasgow constructed in 1967. By discussing the fire safety features designed into my block, we can perhaps interpolate those into Grenfell to establish what should have happened that night.

It should be noted at this point that Scottish building codes have differed from English codes for many years, but ultimate objectives are always the same: save life; reduce property damage as far as possible, and prevent fire spread.

My Glasgow block, 1967

First, a definition: ‘fire compartment’ – An area contained within four walls, a floor, and a soffit in which a fire will be contained for a specified period of time.

I have used the words ‘flat’ and ‘apartment’ as interchangeable in this article.

The description of the apartment entrance doors in my block is from memory. They were heavy (solid core?) and were on self-closing sprung hinges (an estimated 30-minute fire resistance).

I remember the continuous pressurisation of the single staircase well. As a 15-year-old, I wondered why air was blowing through the staircase, making the door difficult to open.

There was no such thing as a ‘stay put’ recommendation in event of a fire in a high-rise block in the 1960s — in fact, there were no recommendations of any sort to the tenants back in the Glasgow of the 1960s.

A typical floor plan of my block is shown in Figure 1. The floor was mirrored on the other side of the back wall of flats 4 and 5. We lived in Flat 2.

Figure 1: Glasgow apartment block layout. Door type D1: self-closing solid core door. Doors D2: self-closing solid framed and ledged door with Georgian wired glass panels. Image supplied

When compared with a typical floor at Grenfell Tower, it will be seen that the Glasgow block was of superior design with regard to compartmentation and smoke control. This may be more of a function of building shape.

In the Glasgow block, each flat was a separate 30-minute fire compartment. Considering a fire in Flat 2 for example, the fire would be contained in that flat until it either, a) Broke a window and vented itself to the outside (hence, the 1m flame travel path requirement between openings in floors), or b) Burnt through the 30-minute fire resisting entrance door and vented into the smoke lobby.

In the unlikely scenario that the fire would first burn through the entrance door, the population of flats 1, 3, 4, 5, and 6 would already have had approximately 30 minutes to evacuate the floor.

Next, smoke and super-heated gases could do two things: a) Break into an adjacent flat through its entrance door — another 30 minutes, giving a one-hour period for fire spread between flats, or b) Spread into the lift lobby.

To be a danger to the remainder of the block, the fire would need to break through the self-closing smoke lobby door and spread into the lift lobby. That’s another, say, 20 minutes — in other words, 50 minutes have passed since ignition. From here, the smoke and heat would be prevented from migrating into the staircase by the continuous pressurisation system. Its path of least resistance would be the lift shaft where it would rise until it reached the head of the shaft, then build back down, spreading out through the lift doors into the lift lobbies on the upper floors. To damage upper-floor flats, the fire would need to break back into the smoke lobbies and then through the solid core entrance doors.

BUT — fire brigade response time from receipt of call to arrival is designed to be less than 10 minutes. Add another five minutes or so to commencement of firefighting and five minutes to extinguish the fire — a total of about 20 minutes. It can be seen that the fire would in all likelihood be confined to the initial fire compartment as in fact it had been in Grenfell Tower, and the ‘stay put’ order used widely in the UK for residents in tower blocks in event of a fire, would be verified.

The more likely scenario would have been that the build-up of heat from the fire inside Flat 2 would first cause cracks in a window. The window would then break, resulting in the fire venting itself to the outside. The fire now has sufficient O₂ for the combustibles to increase their burning rate and the eventual result would be a flashover. After a period of approximately 30 minutes, the fire would burn its way through the entrance door but, as we noted earlier, fire brigade intervention would have extinguished it at around 20 minutes.

Grenfell Tower

Figure 2 shows a typical floor plan in the Grenfell Tower block.

Figure 2: A typical floor in the Grenfell Tower block. Image supplied

Interpolating the above design to Grenfell Tower, the original design should have ensured that the flat entrance doors were at least self-closing solid core doors, ensuring each flat was a separate, ±30-minute fire compartment. A fire in Flat 2, for example, would have been subject to the same behaviour as for the Glasgow flat, and fire brigade intervention would have extinguished the fire — as it did, within the specified fire resistance time of the fire compartment.

The major difference in design of the two blocks is the lack of smoke lobbies in Grenfell. In the event of a fire breaking through an entrance door after 30 minutes, the lift lobby would become smoke logged immediately; residents in adjacent flats could be trapped (if they happened to ‘stay put’), as access to the staircase is blocked by smoke. However, fire brigade intervention was fast enough to prevent this from happening.

(It is unknown at this stage if the staircase was pressurised.)

To sum up compartmentation

A fire initiating within a properly compartmented enclosure (flat) will be contained within that enclosure rather than spread to adjacent enclosures for at least the specified fire resistance of the fire compartmentation. As in this case, the fire may vent itself directly to the outside via a broken window, but may be prevented from spreading to the flat above by the 1m flame travel path requirement between openings in floors (although this itself is a somewhat debatable issue).

Simple compartment fire dynamics

Ignition is the first part of the process. It can be produced either by a flame or by spontaneous combustion. Flat fires are usually caused by an ignition source such as a flame or over-heating.

The next stage is growth. This depends on the type of fuel and the amount of oxygen available, and can either be fast where fuel and oxygen available are sufficient for flaming combustion, or be a slow smouldering process — this type of fire may eventually burn itself out. Normally, the heat that accumulates at the upper level of the compartment reaches the point where it cannot absorb additional heat as fast as it is being created. This causes the heat to be pushed back down onto the lower level fuels, for example furnishings/cupboards/carpets at floor level. The temperature of these fuels will rise steadily during this phase of the fire.

In addition, a portion of the windows within the flat will be within the upper layer of the heat band, and a portion will not. The windows will crack due to thermal stress. When there are sufficient cracks in a window, usually four — one from each corner radiating inwards towards the centre — portions of it fall out. The fire now has as much O₂ as it needs to consume the combustibles.

The temperature rise required to break window glass is ≈100°C. The gas temperature rise required to produce flashover is between 500°C and 600°C. In most fires, window breakage occurs before flashover. Window breakage ventilation has a major effect on fire growth to flashover.

Flashover is the condition that occurs when all of the combustible materials in an enclosure ignite simultaneously. This happens at around 500–600°C. The flashover ends the growth phase, where you may still find victims alive in the room or compartment. After flashover, the fire enters the fully developed phase, and any victims in the compartment become body removals. Flashover is not time-dependent. Some flashovers can occur within three minutes from ignition, others may take considerably longer. Flashover times are mainly dependent on the size of the enclosure, the fuel load and type within it, and the construction of the enclosure.

After flashover follows the fully developed fire. At this stage, the energy released in the compartment is at its greatest. The O₂ required for combustion enters from the bottom of the broken windows, and the super-heated gases leave through the top of the same openings. The temperature of these gases varies between 700°C and 1 200°C.

The last phase of the fire is decay. As the fuel is used up, the energy released reduces, along with the temperature, until without intervention, self-extinguishment takes place.

The phases are shown graphically in Figure 3.

Figure 3: Phases of a fire. Image supplied

So, what happened at Grenfell Tower?

Grenfell Tower underwent a major renovation between 2015 and 2016. New window frames and a new aluminium composite cladding were installed on the facade of the building. Beneath these, and fixed to the outside of the walls of the building, was a thermal insulation. An alternative cladding with better fire resistance was available but not used due to cost.

Designer’s note

The newly renovated facade of the building is believed to have been built as follows:

• Exterior cladding: aluminium sandwich plates (3mm each) with polyethylene core;
• A ventilation gap (50mm) between the cladding and the insulation behind it;
• An insulation made of polyisocyanurate (150mm) mounted on the existing facade;
• The existing prefabricated reinforced-concrete facade; and
• New double-glazed windows.

It is alleged that both the aluminium/polyethylene cladding and the insulation failed fire safety tests conducted after the fire.

“Original designs usually meet the objectives of the fire regulations. Problems arise with change of building usage, illegal alterations, or legal alterations carried out without reference to original design objectives.”

The UK generally has a ‘stay put’ policy for folks in the event of a fire in a high-rise building. This policy is based on a knowledge of compartment fire dynamics, compartmentation, and early fire brigade intervention times.

Grenfell Tower – a hypothetical timeline

1. 1. An electrical short circuit occurred in a fridge/freezer in a flat on the fourth floor.
2. 2. The fire spread from the fridge to adjacent combustibles.
3. 3. Compartment temperature reached ambient plus ≈100°C.
4. 4. A window in the flat broke, allowing flames to lick out the window against the exterior cladding.
5. 5. The fire spread unnoticed into the 50mm ventilation gap between the insulation and the aluminium sandwich panels.
6. 6. The original fire in the fourth floor flat was extinguished by the fire brigade. As they were making to leave, firefighters noticed fire spreading up the facade of the building.
7. 7. The panels and/or insulation had started burning, and the fire plume extended vertically and horizontally through the ventilation gap, acting as a primitive jet pump.
8. 8. The burning panels/insulation caused flaming combustion. The temperature of the windows of the so far unaffected flats were raised by ≈100°C or subjected to uneven heating from the external fire, causing thermal stress, which in turn caused them to break. Flames licked inwards, igniting curtains and other combustibles within the flats. Flashover eventually occurred in some of these flats due to non-fire brigade intervention.
9. 9. At this stage, fires within affected flats would vent back out of the broken windows. The temperature of the super-heated gases venting through the broken windows would exceed the melting temperature of the aluminium panels (550°C), further contributing to ignition of the polyethylene cores and the polyisocyanurate insulation, thus accelerating the combustion/flame spread up and across the facade of the building. Wind effect and stack effect would have had a considerable effect on the heat release of the fire, especially on the higher-level floors.
10. 10. By this stage, the fire growth both vertically and horizontally through the facades of the building had become self-propagating and beyond the control of any form of firefighting. It is estimated that the fire raged out of control within 30 minutes — some say 15 minutes.
11. 11. Inside the building, the single staircase became smoke logged and unusable (compelling me to believe that the staircase was either not pressurised, or pressurised but the system was not working). Smoke spread to lift lobbies via the lift shaft, trapping people in their apartments. They were forced to await a rescue effort, which had quickly become impossible. The fire eventually broke into these flats in numerous places via their windows and probably doors.
12. 12. Some residents would have died from smoke inhalation; others when the contents of their flats flashed over, killing them.
13. 13. The fire burnt on for more than 24 hours, and it was days before anyone could enter the building due to the heat build-up in the structure.

Conclusion

Fire regulations are reactive by nature. Every time a disaster occurs, investigations take place, lessons are learnt, and regulations are changed to prevent a recurrence.

Original designs usually meet the objectives of the fire regulations. Problems arise with change of building usage, illegal alterations, or legal alterations carried out without reference to original design objectives.

It is said that every building will have at least one fire during its lifetime. In 2014, there were 294 apartment fires in South Africa, with two deaths. Damage was estimated at R164 670 830. (Fire Protection Association)

Hopefully, South Africa will be spared its own version of Grenfell Tower in the future.

About the author

Jock Litterick is a self-employed fire consultant. He spent 15 years with WSP Consulting Engineers as a senior fire engineer and principal associate. Prior to that, he was with Delen & Oudkerk Consulting Engineers for 10 years. He was first introduced to the consequences of fire in 1977 when he joined the Durban Fire Department. He left the department in 1989 with the rank of divisional officer: fire prevention. Jock hails from Glasgow, Scotland, and has been in South Africa for 49 years.