Why the Fire Spread So Quickly: The Cladding
The fire in flat 16 should have remained a contained kitchen fire. Instead, it engulfed a 24-storey building. The primary reason was the material wrapped around the outside of the tower.
The ACM Cladding
The most significant element of Grenfell’s 2012-16 refurbishment was the addition of external cladding: aluminium sheets bonded to a central polyethylene (plastic) core. In his report to the Public Inquiry, Professor Luke Bisby concluded that this material was the primary cause of the fire’s rapid spread.
The polyethylene filler is highly combustible: it melts, drips and flows at elevated temperatures, releasing large amounts of energy during combustion.
Adapted from Prof. Luke Bisby’s report to the Grenfell Tower Inquiry
Bisby also found that vertical cavities within the cladding structure acted as chimneys, accelerating the upward spread. Insulation behind the panels and a pre-existing polyurethane foam board may also have contributed.
- Combustible corePolyethylene within the ACM panels
- Heat and combustionMaterial melts, drips and releases energy
- Upward spreadVertical cavities act as chimneys
A Cascade of Failures
The cladding was not the only problem. The Inquiry identified a series of additional failures that compounded the disaster:
- Window materials
- Combustible materials used in the refurbished windows allowed fire to enter flats from outside.
- Smoke extraction
- The system was designed for a fire on one floor; the Inquiry identified weaknesses in its design and verification.
- Water supply
- Water reached firefighters inside the tower through a dry rising main. Flow rates were low on the night, partly because of pressure losses between distant hydrants and the fire appliances.
- Gas pipes
- The boxing-in of new gas pipes in the lobbies had not been completed at the time of the fire. The Inquiry found that gas did not play a significant part in the fire’s spread.
- Fire doors
- Many replacement flat entrance doors did not meet the required standards.
- Lifts
- Firefighters could not take control of the lifts using the fireman’s switch, although they could still use them in normal operation.
Sources: Grenfell Tower Inquiry, Phase 1 report, vol. 1, para 3.24; vol. 4, paras 24.3–24.6, 34.11 and 34.15 [R019]. Grenfell Tower Inquiry, Phase 2 report, vol. 3, paras 40.7–40.8; vol. 4, paras 60.111–60.116; vol. 5, paras 81.14–81.21 [R015].