While fire safety and regulations have always been a high priority in building standards, in the aftermath of events such as London’s Grenfell Tower fire that killed 72 people in 2017, those requirements have become even stricter.
Consequently, when specifying building products and systems, architects and contractors must be familiar with the fire-related regulations as well as testing procedures and performance classification levels.
What follows is an overview of current European fire standards, testing and certification levels with a special emphasis on polycarbonate’s unique ability to withstand fire in comparison to other transparent plastic materials.
European Standard EN 13501-1
Whereas in the past, every European country had its own building product certification mechanisms in place, this changed when the European Union established the Harmonized Standard to increase the uniformity and quality of standards throughout European countries and beyond. A significant number of countries in Asia, the Middle East and Africa, as well as Russia, have either adopted the Eurocodes or have expressed interest in code adoption.
Impact on Fire Regulations
European Standard EN 13501-1: Fire classification of construction products and building elements defines the testing procedures to assess and classify a material’s reaction to fire. Per the standard, which applies to all building products, the material must be tested in an approved laboratory in the same way that it will be installed in a building.
The EN 13501-1 test allows for testing a range of thicknesses and colors. For example, if a 1 mm and 10 mm thick sheets are tested and pass, then all intermediate thicknesses are certified. Similarly, if a manufacturer tests their brightest color, darkest color and one intermediate color and pass, then it is
considered that other colors also pass.
Euro Class Definitions
Based upon how well the material performs when exposed to fire, a class category is then assigned as follows:
- Class F – Easily flammable
- Class E – Small flame test duration of 15 seconds with less than 15 cm flame spread
- Class D – Small flame test duration of 30 seconds with less than 15 cm flame spread and a heat release of 750 watts per second or less
- Class C – The heat release from a single burning item is less than 250 watts per second.
- Class B – The heat release from a single burning item is less than 120 watts per second.
- Class A2 – The material passes a no combustibility test in a furnace of 750 degrees C or a calorific potential test, which is performed by burning a small amount of the material in pure oxygen inside a bomb calorimeter.
- Class A1 – The material passes both a non-combustibility test and a calorific potential test.
Furthermore, for A1, A2 and B Euro classes, the material experiences no flashover, which means that contribution to a fire is minimal. For C, D, E and F, the material can cause flashover in a fire test.
To achieve A2, B, C or D classification, the material is also rated by how much smoke and flaming droplets it releases.
- A product releasing little or no smoke receives an s1 classification, a medium level of smoke is categorized as s2 and a product generating a lot of smoke, thus making escape more difficult, is classified as s3.
- Flaming droplets or particles can inflict skin burn and cause fire spread. A d0 rating means that the product creates no flaming particles when exposed to fire for 600 seconds. A d1 classification means that flaming droplets are released in this time period, but do not burn for more than 10 seconds. A d2 level applies to materials that release droplets over a period of 600 seconds which burn for more than 10 seconds.
Polycarbonate’s Reaction to Fire
A highly effective building material, polycarbonate (PC) is lightweight, impact resistant, durable, easily moldable and long lasting. At half the weight of glass, how do translucent and transparent polycarbonate sheets stand up to fire?
The material offers two main advantages in the way it reacts to fire. Firstly, without any special additives, polycarbonate certifies as Class B, which means the sheet minimally contributes to fire spread. Therefore, if a fire starts in a building, once it reaches the polycarbonate, the material will not prevent the spread of fire. However, the rate of spread will be very slow, particularly when compared to other combustible materials. Secondly, untreated Polycarbonate will produce very little smoke in the presence of a fire. This is significant as Stanford Medicine reports that smoke accounts for approximately 70 percent of fire victim deaths.
Polycarbonate has a classification of s1, which means that the speed or quantity of smoke is absent or very low. In addition, polycarbonate produces very little flaming droplets, which contribute to the spread of fire by igniting other surfaces, and therefore receives a d0 rating per EN 13501-1.
To better understand the material itself, polycarbonate has a very wide service temperature, ranging from -50 to +120 degrees C. At about 135 degrees, it reaches the Heat Deflection Temperature and starts losing its physical properties. At around 140 degrees, the sheet starts to deform, which eventually results in the material folding or collapsing out from its frame or whatever it is that’s holding it in place.
Between 160 and 170 degrees, the sheet begins to transform into a melted material at which point it starts dripping.
This melting phenomenon can help extinguish fire in cases where it melts directly on the flame source. At the same time, this can make testing difficult as the melted Polycarbonate may drip onto the burner and turn off the flame, thereby stopping the test before a classification can be given. As such, a solid polycarbonate sheet that is thicker than 6 mm cannot be tested as it will douse the fire upon melting.
However, polycarbonate multiwall sheets can be tested even if they are very thick. This is because there is lots of air and relatively little material to melt in this variation of the product.
Polycarbonate typically receives a grade of B, s1, d0 under EN 13501-1.
Solid Polycarbonate vs. Multiwall Polycarbonate
For architects and building owners it is important to understand not only the regulatory requirements and details of the EN lab testing, but also how the different types of Polycarbonate sheets will react to fire when installed.
One important distinction is between solid and multiwall Polycarbonate. Solid Polycarbonate is normally heavier since it contains more material per square meter whereas multiwall sheets contain air channels or flutes.
Take, for example, a vertical glazing application, which can use either solid or multiwall Polycarbonate sheets. In the case of fire, the multiwall will burn faster and create a hole in the glazing. If the fire source is internal and the hole allows the smoke to escape from the room outwards, this is beneficial. On the other hand, a solid sheet will perform better in stopping the spread of fire, which is key if building occupants are located on the other side of the glazing. In a roof or canopy application, again the multiwall sheet will allow burning to occur faster, creating a hole and allowing the smoke to escape.
Fire Retardant Additives
During the polycarbonate extrusion process, the manufacturer can add fire retardant (FR) additives to the Polycarbonate sheet. These additives do not harm, reduce nor degrade the material’s natural physical and optical properties. Further, in the event of fire, FR can improve the properties of the Polycarbonate sheet.
The way the additive reacts to fire is by creating a fog like environment very close to the surface of the sheet. This “fog” then works to dilute the gaseous oxygen and thus inhibits the burning process. The FR raises the melt flow index and causes the sheet to become more viscous and slower to melt. This, in turn, reduces dripping.
In the EN 13501-1 test environment, polycarbonate without FR is not considered a dripping material and receives a d0 rating. Therefore, from a purely fire regulatory perspective, there is no benefit to the use of FR since the classification will stay the same.
Comparison to other Transparent Plastic Materials
Polycarbonate offers a noted advantage over acrylic with respect to fire. Acrylic is considered a combustible material and performs much worse than Polycarbonate in fire tests. In comparison, Polycarbonate offers a much better combustibility grade and dripping grade. Concerning smoke development, there is no big difference between the two materials.
Regarding PVC, the material develops more smoke than Polycarbonate. However, thin PVC sheets are less flammable than Polycarbonate.
Fiberglass is more flammable than Polycarbonate. In order to achieve good test results with fiberglass, a lot of FR additives are required, which then makes the material more expensive than Polycarbonate.
Faced with meeting stringent fire tests and requirements, architects and specifiers will be more equipped with a better understanding of EN 13501-1 fire classification levels. Further, in evaluating transparent plastic materials, a more in-depth understanding of polycarbonate, its reaction to fire and Euro class ratings can help determine which materials will meet project codes and requirements.