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TRIAL BY FIRE FOR PVC

01-07-2020
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By Sophi MacMillan, chief executive of the Vinyl Council of Australia

The latest technical guidance on PVC fire safety, the 2019 ISO Technical Report, has highlighted the inherent performance benefits of the material in the event of fire.

When subjected to a series of tests, the inherent flame retardancy of PVC proved not to cause, support or enhance the development of fire, particularly when used in windows or building products.

Better known as vinyl, PVC is the most widely used polymer in building and construction, with up to 70 per cent of global annual PVC production used in the sector.

Over the last 60 years, the material’s increasing use in construction and furnishing of buildings has led to a thorough assessment of its fire performance.

The results show a distinct advantage of uPVC (unplasticised or rigid PVC) over many other building materials, including timber, in the event of fire.

The chlorine content of PVC, particularly uPVC, acts as a natural fire retardant, giving it inherently superior fire performance and setting it apart from other polymers such as polyethylene.

Unlike most timber building elements, uPVC does not support combustion and is in fact self-extinguishing. In reaction to fire tests, the report states that due to its high content of chlorine, uPVC “displays a high resistance to ignition, a low rate of heat release, and self-extinguishes when the external heat source is removed.”

Another reason uPVC is far less likely to burn is due to its resistance to ignition. The temperature required to ignite uPVC (391 degrees C) is higher than that needed for wood (260 degrees C).

The report compares data of some results for PVC with those of other materials regarding ignition times and heat flux values to cause ignition respectively “illustrate the good ignition resistance” of PVC materials.

Most PVC formulations are not just difficult to ignite – they will self-extinguish when the flame source is removed because of the high levels of chlorine present in PVC. This makes the material particularly suitable for rigid applications such as windows, doors and permanent formwork and lining used in construction; a significant positive for fire safety.

This chemical makeup also ensures that burning uPVC chars and will self-extinguish if the external heat or flame source is removed. This, and the fact that uPVC rarely produces flaming droplets or burning debris, makes the material inherently resistant to flame spread.

The flame spread index (FSI) value of uPVC generally sits around 15-20. In comparison, Douglas fir or cedar plywood has an FSI value of 190-230.

uPVC permanent formwork systems have been tested to AS5113 (BS8414) façade test and successfully passed the no flame spread criteria, and tested to AS1530.3 to achieve Spread of Flame Index of zero.

Heat release is a key factor regarding fire safety. Data on measurement of peak heat release rates (PHRR) and fire performance index (FPI) values shows that PVC materials “behave well” when compared to other polymers and timber.

In room-corner fire tests on wall linings, the PVC systems outperformed wood, polycarbonate and FR ABS among others, with substantially lower average and total heat release rates. None of the PVC materials caused flashover.

The study also showed that the low flame spread and low heat characteristics of PVC materials tend to also exhibit low smoke release. Burning PVC releases a heavy smoke, but tests show that PVC materials don’t present a smoke hazard significantly greater than many other commonly used materials.

In the context of fire safety objectives, survey data shows up to 15 per cent of all plastics in a private house are in construction products. A much higher proportion (85 to 90 per cent) of plastics are brought into a building by the occupants, such as furniture, household and technology appliances, toys and packaging.

PVC, a strong, recyclable and versatile building material with inherent fire retardancy, is an excellent, safe and long-life choice for myriad construction applications.

While people are naturally concerned about combustibility of plastics, it’s important to understand the difference between the characteristics and properties of different polymers. Crucially, it’s PVC’s high chlorine content of 57 per cent – a fire retardant – that sets it apart from other polymers.

Australian manufactured uPVC permanent formwork systems have extensively been fire tested to demonstrate their fire performance compliance with the relevant requirements of the NCC.

PVC is undoubtedly one of our most successful modern synthetic building materials to undergo rigorous assessment of its effects on health and the environment. It’s time to reassess our attitudes toward this proven safe material.

Specifiers, architects, construction and fire professionals can learn more about the material’s credentials in the 2019 ISO Technical Report: ‘Plastics – Guidance on fire characteristics and fire performance of PVC materials used in building applications’, which serves as a valuable technical reference document for the specification of PVC products at the design or pre-building phase.

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