Technical report highlights good fire performance of PVC
PVC used in windows and building products has proven performance benefits in the event of fire due to its inherent flame retardancy, that will not cause, support or enhance the development of fire. Sophi MacMillan, Chief Executive of the Vinyl Council of Australia analyses the latest technical guidance on PVC fire safety.
PVC, or vinyl, is the most widely used polymer in building and construction applications with up to 70% of global annual PVC production used in this sector. Plastic products contribute to greater building energy efficiency, cost savings, construction safety, lower embodied carbon and design versatility.
The material’s increasing use over the last six decades in construction and furnishing of buildings has led to a thorough assessment of its fire performance that shows the distinct advantages of uPVC (unplasticised or rigid PVC) over many other building materials, including timber, in the event of fire.
Crucially, PVC, especially unplasticised PVC (uPVC or PVC-U) has inherently superior fire performance due to its chlorine content that acts as a natural fire retardant, setting it apart from other polymers such as polyethylene.
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.
So, what are the benefits of PVC fire performance characteristics and how can these contribute to enhanced safety in the event of fire?
uPVC is inherently fire retardant
The high chlorine content of uPVC acts as a natural flame retardant, greatly reducing its combustibility. Unlike most timber building elements, uPVC building elements (such as window frames and permanent formwork) do not support combustion and are in fact self-extinguishing.
In reaction to fire tests, the report states that due to its high content of chlorine, ‘PVC-U displays a high resistance to ignition, a low rate of heat release, and self-extinguishes when the external heat source is removed’.
uPVC is slow to ignite
uPVC is far less likely to burn due to its resistance to ignition, thus contributing to fire safety. The temperature required to ignite uPVC (391 degrees C), such as that used in window profiles and permanent formwork, is higher than that needed for wood (260 degrees C).
The report’s comparison 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.
uPVC is self-extinguishing
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 PVC particularly suitable for rigid applications such as windows, doors and permanent formwork & lining used in construction, and is a significant positive for fire safety.
uPVC has a limited flame spread compared to other materials
Burning uPVC chars and will self-extinguish if the external heat or flame source is removed, making it inherently resistant to flame spread. It rarely produces flaming droplets or burning debris, which are a major cause of flame spread.
Generally, uPVC profile has a low flame spread index (FSI) value of 15 to 20. In comparison, Douglas fir/cedar plywood FSI value is much higher at 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 0.
uPVC heat release
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.
For example, uPVC permanent formwork systems have been tested to AS1530.3 to achieve Heat Evolved Index of 0.
In room-corner fire tests on wall-lining materials, the PVC systems outperformed the others, including wood, polycarbonate and FR ABS, 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/low heat release characteristics of PVC materials tend to also exhibit low smoke release.
uPVC smoke density and toxicity in fires
Burning PVC releases a heavy smoke. However, smoke measurement tests show that PVC materials do not present a significantly greater smoke hazard than many other commonly used materials.
PVC and fire safety
In the context of fire safety objectives, survey data shows that only 10% to 15% of all plastics in a private house are in construction products. A much higher proportion (85% to 90%) of plastics are brought into a building by the occupants, such as furniture, household and technology appliances, toys and packaging.
As a strong, recyclable and versatile building material, with inherent fire retardancy, PVC is an excellent safe and long-life choice for myriad construction applications.
In Australia, uPVC window frames have been developed and tested specifically to meet construction requirements for designated Bushfire Attack Levels (BAL) within Australian Standards for Construction in Bushfire Prone Areas (AS 3959:2009), with uPVC permanent formwork reinforced concrete wall systems able to meet BAL FZ (flame zone) construction requirements.
uPVC windows with metal reinforcing are permitted in zones classified as up to BAL-29 (where the number represents the heat flux in kW m²) risk. Some u-PVC window systems have been independently tested and comply with AS 1530.8.1 which permits their use in zones BAL-40 and above.
While people are, naturally and rightly, concerned about combustibility of plastics, it is important to understand the difference between the characteristics and properties of different polymers. And crucially, that PVC’s high chlorine content (57%) - a fire retardant -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. These fire tests include (but are not limited to) AS5113 (BS8414) façade fire test, AS5637.1 (ISO9705) room test classification test, AS1530.4 fire resistance level testing, and AS1530.3 fire hazard indices test.
PVC is undoubtedly one of our most successful modern synthetic building materials that has undergone rigorous assessment on its effect on health and the environment. It is time to reassess our attitudes towards this proven safe material.