The Grenfell Tower fire: Not a failure of the fundamental Fire Safety Strategy but rather a failure to adhere to it.

As the death toll rises and the magnitude of this horrific event sinks in, we hope that thought-through comments and appropriate actions will replace the unqualified and misleading reporting that we've seen so much of, over the last few days.

The terrifying speed of fire spread and the devastating consequences for so many people, are not the result of the

• "stay put" policy
• lack of sprinklers
• lack of multiple escape stairs
• lack of communal fire alarm or public address system

Yes, of course, if any or all of these additional measures were in place then the consequences may not have been as severe, but this does not necessarily imply these measures should have been in place, or that we should race and use up resources that could be more effectively used in saving more lives in other aspects of fire safety.

The current fire safety strategy for blocks of flats and its effectiveness (fire statistics)

The most fundamental premise of our fire precautions and life safety strategy for blocks of flats is effective fire compartmentation. This translates to enclosing each apartment/flat and common means of escape (corridors and stairs) with fire resisting walls, the concept being that a fire within an apartment will be contained within that apartment for sufficient time to allow the contents to be burned out or for the Fire Service to extinguish the fire without the fire transferring to other areas of the building. Effective fire detection within each flat should give an early warning to the occupants of that flat to evacuate while the fire is small, while the occupants of the other flats need not do anything - hence the "stay put" policy. Nothing else is needed and a single protected escape stair is adequate for the number of people evacuating at any one time.

This is a simple and effective system and has served us well for the last 50 to 60 years. When implemented correctly there is very little that can go wrong. Statistics clearly show that the strategy has been successful. Every year 25% of all dwelling fires, that's approximately 10,000 fires a year, occur in blocks of flats. Proportionately (per user) there is a higher frequency of occurrence of fires in blocks of flats rather than other dwellings, but the number of casualties per fire in these fires is slightly less than other dwelling fires, suggesting fires are of similar severity and conditions. The vast majority of fires are contained within the flat (and, in the majority of cases, the room) where they started. It is certainly rare for anyone, outside the flat where a fire starts, to die as a result of a fire in a flat.

So, over the decades and hundreds of thousands of fires in block of flats there is no evidence from fire statistics to suggest that those living in purpose-built blocks of flats are at greater danger from fire, once it breaks out, than those who live in houses, clearly supporting and validating the compartmentation strategy for apartment blocks.

So what went wrong at Grenfell Tower?

As compartmentation is the basis of our fire safety strategy in blocks of flats, it is critical that this compartmentation is maintained at all times. This becomes particularly important when making modifications and upgrades to the building and especially when we have services going from one compartment to another through, so called, penetrations. Unless remedied, these penetrations can become a route for fire spread and thus a breach of the compartmentation principle. We believe we have good standards and good testing regimes that should ensure that such penetrations are adequately fire-stopped, preserving thus the fire separation. There is significant evidence, however, that in practice some contractors do not actually implement fire stopping of penetrations to the required standards mainly because such penetrations are typically concealed allowing cost-cutting shoddy workmanship to pass unnoticed.

It is possible that following the recent renovation works and upgrade to the Grenfell building that there might have been residual failures of internal compartmentation through incorrectly protected or unprotected penetrations. These would have contributed to the internal rapid fire spread within the Grenfell Tower. For certain the Inquiry will look in detail for such possible failures.

However, we don't have to wait for the Public Inquiry to conclude that the major mode of failure of the building compartmentation came from the combustible external cladding of the building.

In any tall building the windows and balcony doors are in effect unprotected penetrations connecting the individual compartments to the outside environment of the building and to the building external facade. As all compartments are connected to the same external space it is then possible that this external space can provide a route for the fire to spread from one compartment to another and hence breaching the compartmentation of the building. If there are no combustible materials in this external environment or on the facade of the building then this breach of compartmentation is difficult to occur but there have been a number of (rare) cases of this happening. However, the presence of a combustible facade, as in the case of the retrofitted insulation and cladding system on the Grenfell Tower, can lead to rapid and uncontrollable fire engulfment of the building externally and internally.

The gap that can exist between the insulation and the external facing material of this cladding systems can exacerbate the fire spread by creating a chimney effect enhancing thus the speed of fire spread. This feature was also present in the Grenfell Tower cladding and fire.

In the last four years there have had many tall building cladding fires across the world many in the Middle and Far East but also in Australia, USA and Russia all of them severe fires but remarkably with a low number of fatalities. We should have taken careful note of these fires but surprisingly it would appear we have not. Did the fortunate lack of fatalities in these fires create an unjustified complacency?

What is the design guidance for facade claddings for tall buildings (over 18m)?

The Building Control Alliance (BCA) published a technical guidance note BCA GN 18 (2015), summarising the main requirements for facade systems and proposing 4 routes to compliance:

Option 1: This option requires compliance with the guidance given in Approved Document B (12.7) and BS9991 (18.2) which specify materials of major components to have limited combustibility. The use of such materials for all major elements of the cladding system both above and below 18m. This includes the insulation, internal lining board and the external facing material. Smaller non critical and low-risk items can be excluded from this requirement - which somewhat confuses the guidance. Materials are deemed to have met the required performance criteria after having been subjected to specific small scale fire tests performed in isolation from all other materials comprising the fa?ade system and therefore not wholly representative of that for the complete system build–up.

Option 2: A performance–based route: The complete fa?ade build–up should meet the acceptance criteria set out in BR 135 (mainly Internal and external fire spread and mechanical integrity ) when subjected to large scale fire tests specified in BS 8414 Part 1 or 2. This a test where a corner configuration assembly of the complete cladding system is subjected to a 30 min crib fire at its base which peaks at 3 MW . The cladding extends to at least 6m above the fire chamber as an uninterrupted surface. This, 6 m continuous surface, is a weakness of this test when the products are tested for buildings like the Grenfell Tower where the presence of windows will change the flow and effects of the hot gases. It is nevertheless a severe test that should provide evidence to an experienced fire engineer of suitability or not for a particular application.

Option 3: Fire engineered assessment of cladding based on test data from similar systems and reasoned facts. This desktop assessment should demonstrate equivalence of a BR135 compliant system. This option is available to allow untested variants of a system that has been tested, to be used without further expensive testing.

Option 4: Approve system as part of a holistic fire engineered assessment of whole building, carried out by suitably qualified fire engineer, taking into account all building factors and demonstrating that the building overall provides reasonable provision for life safety.

Under which option from the above was the cladding system for the Grenfell Tower approved?

This we don't know at present and it is something that will likely to only come out as part of the Inquiry, as the parties involved in the approval of this system, (as well as the Responsible Person under the Fire Safety Order) will have a large part of the burden of responsibility.

At least some of the main individual components of the installed cladding system were evidently highly combustible and therefore compliance could not have been demonstrated under Option 1 above. It is unlikely that the assembly would have performed satisfactorily in the BS8414 test given its performance in the actual fire, therefore demonstration of compliance under option 2 is highly unlikely.

[Edit 25/06] It has been reported in the media that the facade system was Celotex RS5000 consisting of 100 to 150 mm Polyisocyanurate (PIR) foam insulation board, weather protected by Reynobond Aluminium Composite Material (ACM) panels which themselves had a relatively thin combustible plastic core. The Celotex RS5000 data sheet claims to have satisfied the criteria of BR135 through the BS8414-2 test. However, in summarising the actual test set up (on the data sheet) it is clear that there are significant differences in the test set up and what was reportedly used in the Grenfell Tower installation. These included 12mm Fiber Cement panels, 12mm non combustible board and 2x12.5 plasterboard.

On this evidence it is possible that approval was obtained by claiming compliance through, most likely, Option 3 above and possibly through Option 4 i.e. the fire engineering assessment routes. From the available information it would take a massive, unjustified leap of faith to claim compliance of the reportedly installed facade assembly with the BR135 criteria and securing approval for this cladding / insulation assembly. [end of Edit 25/06]

If this is indeed the case, this will bring much embarrassment and disrepute to the Fire Engineering profession and will raise many other pertinent questions, particularly since it is transpiring that many other buildings have been shrouded in similarly dangerous cladding systems. What was the input the other interested parties, Building Control, Fire Service? Where is the oversight and the checks in this process - why and how did they fail? How did we allow this to happen?

What about Sprinklers?

Another question that is frequently asked is: Could sprinklers have prevented this from developing the way it did?

The answer to that is: it is possible that if the fire was in the right location its growth could have been controlled by an activated sprinkler. Sprinklers are not designed to put fires out but to control the growth until extinguished by the Fire Service. So it is perfectly possible that the hot fire gases venting out of an apartment could have still ignited the cladding.

Sprinkler systems are designed to deal with one growing fire in one location at any one time. They are designed to deliver water at specific rate to deal with the likely fire size and to achieve this, only a defined small number of heads can be delivering at the same time. If more heads are activated then the flow rate is reduced below the minimum required and the fire starts to grow again and the sprinkler system effectively fails.

In the Grenfell Tower fire, once the cladding was ignited and the fire was transferred to the other apartments then it would have activated more sprinkler heads that would have caused the sprinkler system to be ineffective and fail.

Could this fire have happened if the cladding was not there?

The simple answer to this is NO. As discussed earlier the building was designed as individual fire compartments and 10,000 other similar fires per year show that the likelihood is that it would have been contained in the initial apartment and its extinguishment by the Fire Service would have been the end of it.

It is worth noting that despite the immense fire the main building structure is still standing and apparently safe for services personnel to enter. This is testament to the original design and construction of the building.

We believe the fire escalated and the catastrophe happened because of the wrapping of the building in combustible facade compromising the fire compartmentation of the building and invalidating the fundamental fire safety strategy for this type of building that many thousands of fire events each year serve to prove that this is a sound strategy.

What causes fatalities and injuries in fires?

This is not a flippant or thoughtless question.

As we mourn the unnecessary loss of so many lives and the injuries and devastation to so many others, we are confident (sadly) that it will transpire that as in all fires, most fatalities were caused by toxic poisoning from the combustion products released during the fire. The initial media reports from hospitals are confirming this. This will have been made significantly worse by the reported presence of Polyisocyanurate (PIR) foam in the cladding which produces high yields of deadly hydrogen cyanide. Many years of statistics, from the UK and the USA, show clearly that 60% to 70% of all fire fatalities in dwellings can be attributed to the inhalation of fire toxic smoke. Furthermore, we are just beginning to appreciate that the inhalation of the extra fine smoke particles with toxic species adsorbed onto the surface produce long term adverse health effects to those who are exposed to them including the emergency services. This is probably the least regulated aspect of fire safety and the industry has been resistant to going down the route of controlling the toxic yields from construction and household products when they are involved in fire. Governments have been reluctant to force the issue.

What are the priorities now?

Irrespective of the course and outcome of the Public Inquiry some the need for immediate urgent action now and it’s assuring to see the relevant authorities working towards some of these.

• Identify which cladding/facade installations have combustible materials in them and remove immediately starting with large residential and sleeping accommodation buildings and prioritising facades that have openable windows.
• Suspend all cladding / insulation installations currently in progress.
• Review the fire safety of all facade installations
• Review the approval process of such installations
• Identify the areas of research that will produce the highest improvements in fire safety. Toxicity of fire smoke is a prime candidate.

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Dr H Phylaktou & Prof GE Andrews 23/06/2017

https://engineering.leeds.ac.uk/courses/PG/8798/fire-and-explosion-engineering