A U.K. government inquiry into the June 2017 Grenfell Tower fire in London that killed 72 people concluded that aluminum composite material (ACM) cladding panels on the building's exterior fed the fire, which began in an appliance in one of the apartments.

The report was released in October and is the first of a two-phase inquiry into the disaster. It said that the fire was started by an electrical fault in a refrigerator-freezer in the kitchen of Flat 16. That fire likely entered the cladding as a result of hot smoke on the uPVC window jamb, which caused it to deform and collapse. The collapse provided an opening into the cavity between the insulation and the ACM cladding panels through which flames and hot gases could pass.

Aluminum composite cladding helped to feed the flames. Source: Evening StandardThe report raised a less likely possibility that flames from the fire in the refrigerator-freezer passed through the open kitchen window and reached the ACM cladding panels. The fire had already entered the cladding before firefighters first opened the kitchen door in Flat 16 at 1:14 a.m.

The report said that a kitchen fire of that relatively modest size was "perfectly foreseeable." However, once it escaped from Flat 16, it spread rapidly up the tower's east face. It then spread around the top of the building in both directions and down the sides until the advancing flame fronts met on the west face near the south-west corner, enveloping the entire building in less than three hours.

Fuel for the fire

The report found that the principal reason why the flames spread so rapidly up, down and around the building was the presence of the ACM rainscreen panels with polyethylene cores, which acted as a source of fuel.

The principal mechanism for the spread of the fire horizontally and downwards was the melting and dripping of burning polyethylene from the crown and from the spandrel and column panels, which ignited fires lower down the building. Those fires then traveled back up the building, allowing the flame front to move diagonally across each face of the tower.

The presence of polyisocyanurate (PIR) and phenolic foam insulation boards behind the ACM panels, and perhaps components of the window surrounds, contributed to the rate and extent of vertical flame spread. The crown was primarily responsible for the spread of the fire horizontally, and the columns were a principal route of downwards fire spread.

Material ban

In 2018, the U.K. government moved to ban the use of combustible materials on the outside of high-rise buildings that are more than 18 m tall. The ban did not apply retroactively where materials had already been installed. U.K. building regulation states that all insulation and filler materials for cladding on high-rise buildings must be of "limited combustibility."

A renovation may have contributed to the building's vulnerability to fire. Source: BBCA police investigation into the fire found deficiencies in the installation of windows, cavity barriers and cladding systems, and their failure to meet building regulations. The original concrete building was compromised by a refurbishment that took place between 2014 and 2016.

The police report said that not only were the cladding material and insulation combustible, but that the design and installation of windows and cavity barriers were improperly done.

The BBC reported just after the fire that Grenfell Tower was built in 1974 by Kensington and Chelsea Borough Council. A two-year £10 million ($12.8 million) refurbishment was completed by Rydon Construction in 2016. Work reportedly included new exterior cladding, replacement windows and a communal heating system. The BBC said that "extensive remodeling of the bottom four floors" was completed, creating nine additional homes and improvements to communal facilities.

Fire's spread

The October 2019 inquiry report said the fire on the outside of the building entered many apartments and smoke spread through the building's interior. As a result, effective compartmentation was lost at an early stage, the report said. This happened because the intensity of the heat was so great that window glass failed, allowing the fire to penetrate into apartments.

In addition, extractor fan units in the kitchens deformed and became dislodged, providing a point of entry. And, a number of key fire protection measures inside the tower failed. For example, although some fire doors held back the smoke, others did not. Some were left open and failed to close because they lacked effective self-closing devices; others were broken down by firefighters or wedged open with firefighting equipment.

Many elevator lobbies had started to fill with smoke by around 1:20 a.m. and some were significantly smoke-logged by 1:40 a.m., the report said. By 2:00 a.m., a "significant number" were heavily smoke-logged.

Until around 1:50 a.m., there was less smoke in the stairs; by then 168 people had escaped. After that time the stairs started to fill with smoke, particularly at lower levels. By 2:20 a.m., the smoke in the stairs posed a risk to life, the report said, even though the stairs were not "absolutely impassable" after that time.

The report said that "compelling evidence" existed that the external walls of the building "failed to comply" with Requirement B4(1) of Schedule 1 to the Building Regulations 2010, in that they did not adequately resist the spread of fire with regard to the building's height, use and position. Instead, the exterior walls "actively promoted it."

The next phase of the investigation will examine in part why architects and engineers who designed the tower's refurbishment considered that it would meet the requirement to resist a fire's spread.