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Fire Ratings : What does fire resistance really mean?
Fail to appreciate the importance of fire ratings and the consequences could be disastrous
Q: In terms of ‘building’ materials, how does large format media fit?
A: Legislation for materials testing is due to building safety and the legislative nature of developed countries. Building materials are subject to industry standards and accepted because we all live and work in buildings. It is the basis for understanding the nature of fire resistance. We must recognise that buildings and their materials have been around longer than graphics.
An authority’s main concern is to the publics it serves, including buildings the public live and work in. All testing standards are directed to building materials and graphics has to find a way to fit with or adapt building standards to suit its requirements. The problem with large format graphics is that they are often an afterthought.
Q: What does ‘flame retardant’ mean?
A: This is a common term misused in the graphics industry to describe a graphic products’ fire resistance. This can cause the end-user and applicator to believe they have a product safe for any environment when, in fact, it is not. Clearly, this is potentially dangerous.
There is often common confusion with this terminology, often used in the same breath as ‘flame proof’ or ‘non-flammable’. Any description that states ‘flame retardant’ means the material or substrate retards or resists burning: however it will burn eventually.
Here are some descriptions:
- Flame retardant/retardancy: Retards or resists a flame. This is normally expressed for a specified time period per the test recommendations
- Flame proof: Resists a flame burn. Certain metals or components either naturally resist flame or are designed specifically for this purpose. They tend to be an expensive option for a building or graphic material and are not normally seen in the graphics industry
- Non–flammable/flame proof: Similar description as above but often used to describe textiles that have been pre-coated to provide extra protection
Rarely would these terms be used to describe a graphics product as they could expose the manufacturer to liabilities. How often do you see ‘waterproof’ watches and cameras? More likely, they will be ‘water resistant to a depth of xxx metres’. In principle, the same applies to fire resistance descriptions.
Q: What are the characteristics of differing, commonly used, country-specific test methods and the new European test?
A: Two commonly used methods are: the German B1 (Brandschacht-Test) and B2 (Kleinbrenner) test; plus the British ‘BS476’ test (parts 6 & 7). The new European standard is ‘EN 13501-1’.
DIN 4102-B1: In this test, the material in question is placed in a burn chamber. Four specimens of a given size are placed over a gas flame which burns for ten minutes. The flame remains in position, meaning it will not ‘follow’ the material as it burns away.
The result is found by measuring the remaining length of burned material specimen, along with the smoke temperature. The specimen starts 100cm long and at least 15cm of unburned/unharmed material must remain after 10 minutes. Smoke temperature must not exceed 200°C. If these conditions are met, the material is considered to have passed B1. Side effects, such as burning material dripping and the amount of smoke are noted on the certificate.
DIN 4102-B2: Specimens are vertically exposed to a flame with the flame touching the surface and edges. After 15 seconds, flame spread is measured against reference marks. The B2 test is passed if no flames reach the reference marks after 20 seconds on none of five samples. Again, any dripping material is noted.
BS476/Part 6: Evaluates the fire propagation on/of a material exposed to flames in a vertical position. The flame is produced by a horizontal gas burner and attacks the material’s surface. Measurements are taken for 20 minutes. A fire propagation index is calculated which describes flame spread.
BS476/Part 7: This also deals with fire propagation of a vertical material, but produces a different output. Like the B2 test, fire propagation speed and distance in a given time are considered. Specimens are exposed to heat from a burner plate and attacked for the first minute by a pilot burner flame, which starts the burn process.
After 10 minutes, the material is judged by comparing fire propagation to reference lines on the original specimen. In addition, the position of the flame/burn 1.5 minutes after the start is taken into account.
EN13823 – SBI: With this new method, the reaction to a specific ‘scenario model’ is tested: the scenario being a single burning item (SBI) located in the corner of a room. Flame propagation and contribution to flame spread are measured. The material is placed in a three-wall-corner (itself inside a flame chamber with exhausts and a flame source) and is exposed to flames from below. Duration 20 minutes. Measurements are taken for heat release, smoke rate and lateral flame spread.
Besides different test environments, the main difference between the commonly used, country-specific test methods and the new European test method is the test’s focus. In B1/B2 and BS 476 Part7, the flame spread is the main concern. In EN13823-SBI the material’s heat contribution is observed. This is not unlike BS476 Part 6. In EN13823-SBI the question is ‘how much will the burning material propagate flame and how much will it contribute to the overall energy created by a fire until the fire gets out of control and consumes everything in its reach: the flashover?
Q: Why only single product tests and why do combinations of materials change the result/invalidate a certificate?
A: With finishing products, single product tests are often performed because multiple combinations of products or layers affect the outcome or test results. With graphics products the variety of combinations is enormous. Consider these examples of possible test combinations:
Example one: Complete finished application that gives the most accurate test results as it reflects the application’s actual use.
- Layer one: Lamination film
- Layer two: Inkjet media
- Layer three: Mounting adhesive
- Layer four: PVC substrate
Example two: Lamination film only, this gives an indication of the product’s performance, but can be misleading due to the properties the stainless steel plate gives to the test sample.
- Layer one: Lamination film
- Layer two: Stainless steel plate
Example three: As this is a single usage product, the only influence on test other than the media itself would be the ink volatility (as per the other applications)
- Layer one: Textile plus inkjet printed layer (solvent or aqueous)
Layer one on its own may achieve a satisfactory fire rating (B1/B2). However, once it is applied to layer two its characteristics will change and it will burn more (or less). This will depend on the type of media and inks used such as water-based versus solvent inks or paper versus plastic media.
Once you apply the other layers the characteristics change once again and the combinations become almost endless, according to the customer’s requirements.
In reality, product solutions for lamination should be tested in the requisite combination to give a relevant application fire rating. This can be limiting to customers because they will construct the application with different products from different suppliers on each layer. However, it is the only sure way to give a true result based on the building regulations and the only realistic and safe way for the finisher to make a recommendation. In practice, each product combination requires a separate test, although this is not always practical or desirable.
Some manufacturers have attempted to overcome this issue by applying laminates to a substrate (such as stainless steel) to achieve a single product fire rating. The issue here is that the laminate will take on the properties of the steel and imply a false sense of security.
Q: What about media and textiles?
A: The situation for textiles is different as the product can be used in isolation, particularly if the user is creating an artistic feature. Thus, single testing is the only requirement for textiles. Also, with textiles it is easier to coat with a fire resistant substance or coating (this can be built into the inkjet coating) unlike laminates where a coating will change the visual characteristic of the lamination film.
Q: How to sum up?
A: It is important to concentrate on providing a solution that is realistic and within the scope of materials used in the graphics industry. Manufacturers, finishers and everyone involved in applying a graphic in a public place need to ensure the materials meet the stringent application requirements while also providing a safe environment.
Wherever you look, advertising and graphics are present: billboards, signage, service areas, exhibitions, museums, shopping centres, stadiums and the like. Understanding the test methods and how they apply to graphics material is an important step in building and maintaining a safe environment. We should always endeavour to provide the safest products.
