How To Test The Flame Retardant Fabrics?

You cannot rely on any flame retardant workwear. 

When speaking of flame retardant workwear, one cannot simply rely on any product available in the market just because it says it is flame retardant. Not all types of fabrics meet flammability standards.

It is crucial for the safety of workers at the workplace that the flame retardant workwear you choose to equip your workers with should be functional, i.e., should possess the necessary flame retardant properties that can ensure protection against workplace hazards like flames, high temperatures, fires, electric arc flashes, etc. Both the employee and the employer should be assured that in case of any emergency, the worker is safe.

Types of Flame retardant fabrics:

Any fabric, natural or synthetic can be made flame retardant by treating them with flame-retardant chemicals. On coming in contact with flames and fires, these chemicals react with the hot gases and turn them into carbon chars that ultimately slows down the burning speed. Ignition and spread of fire are also inhibited protecting the worker and giving him/her enough time to escape the hazardous environment.

The different types of flame retardant fabrics can be broadly classified as:

1. Fire retardant (FR) fabrics:These are manufactured by applying a chemical finish to the fabric which can either be natural or synthetic. Flame retardant properties may start declining over time, maintenance, washings and various other environmental conditions.
2. Inherently flame-retardant fabrics (IFR):These fabrics are constructed with yarns that are manufactured with flame retardant additives. Here, the chemical and molecular structure of the fibre is modified. Therefore, this chemical treatment imparts flame-resistant properties to the fabric over its entire service life. At Xinke Protective Technology Co. Ltd., polyester fibres are permanently bonded with FR additives during the dyeing and finishing process of fabric formation.
3. Flame Proofed (FP):FP fabrics are manufactured by treating the fabric with a non-permanent, registered, FR chemical. This topical treatment gives limited service life to the fabric.
   1. Flameproof cotton:When 100% cotton is made flameproof, it cannot stand up to high humidity and washing.
   2. Flameproof polyester:This stands better than flameproof cotton but may require subsequent re-treatment.

Factors that govern flammability of flame retardant fabrics:

 Several factors decide the flammability of fabric. Some of the commonly known and factors worth considering are:

1. Weight:Heavier the fabric, the slower is the burning.
2. Weave:Tightly packed fabrics burn slowly than loosely packed fabrics.
3. Composition:Many times, single fabrics are used and at other times, there may be fabric or non-fabric components added to the base fabric. Synthetic fibres tend to melt rather than burning and can cause serious burns when the molten fabric comes in contact with the skin.
4. Construction (Processing steps):Length of time in service, sewing, printing, painting or any other added processing steps can affect the functionality of the final workwear.

 Why would you need to perform testing procedures for flame retardant fabrics?

The flame retardant workwear that is crafted using the fabrics that qualify necessary tests and meet flammability standards are the ones that you should look for since they assure that the worker will remain safe when exposed to flammable hazards at the workplace.

Safety workwear has many challenges to overcome before it can be relied upon when worn at the workplace. Most of the fire injuries at the workplace can be attributed to the accidental ignition of upholstery and textiles. This tells us how important are fabric testing procedures in the textile industry.

 Tests for flame retardant fabrics:

Here is your ultimate guide to selecting the best flame retardant fabrics. There are several tests that the fabrics have to qualify for being able to be used in certified flame retardant workwear.

Firstly, there is no single standard or test that is used across the globe to address the flammability issue associated with workwear. Different standards and norms are in force across international boundaries. However, for protective workwear, standards laid by the National Fire Protection Association (NFPA) are taken into consideration.

#1. Thermal stability: For testing the thermal stability of the fibre material, the tests performed include:

1. Thermogravimetric (TG) Analysis Technique:It provides information related to a textile material’s decomposition but lacks on providing insight into the fibre’s combustion in oxygen.
2. Cone Calorimetry:It tells the heat release rate of plastics but is seldom used for textiles.
3. Differential thermal analysis method (DTA)
4. Differential scanning calorimetry method (DSC)
5. Thermo-mechanical analysis (TMA)
6. Dynamic mechanical thermal method (DMA)

These methods however have various limitations since they are mostly qualitative. They don’t give an idea as to how long can the protection last and how much protection do they provide.

#2. Limiting Oxygen Index (LOI-value): This is a quantitative method that defines a material’s ability to ignite. But it has a limitation and that is it does not provide any critical information on peak heat release rate.

#3. Performance testing by Fabric Vertical Flammability Testing Method: This is a qualitative method and hence its limitation is that evaluating small differences in flame retardant fabric samples becomes difficult.

As directed by the NFPA, these tests are necessary to test for the fabric’s performance for being thermal protective. These include:

1. The Thermal Protective Performance (TPP):The thermal protective fabric is exposed to high heat flux conditions and its performance at extreme temperatures is evaluated for various parameters like:
   1. ability to resist charring, degrading and shrinking.
   2. ability to reduce the transmission of energy to the skin and the corresponding reduction in the extent of an injury.

The standardizations for different methods of performing the TPP test vary mostly with the source of the ignition being different. Example: The ASTM D4108-87 standardization testing method uses a single laboratory gas burner as the heat source.

Advantages:

• convenient
• precise
• relatively inexpensive

Limitations:

• limited to certain heat exposure sources
• limited to the configuration of test fabric
• no information on spatial effects
• no information on the effects of garment design and construction, nor the role of seams, closures, pockets or vents in the final product.

1. Thermal Radiation Protective Performance (RPP) Test:This is a vertical flame test where the specimen is subjected to a particular heat source from a specified distance. Time taken for human skin to get a second-degree burn is calculated. The calculated RPP value with various parameters taken into account indicates the heat radiation performance of the fabric.

Advantage:

• Indicates the heat radiation performance of the fabric.

Limitation:

1. A quantitative estimate of burn cannot be drawn.
2. Heat Flux Test Method:This is similar to the RPP method with difference in heat source and more number of parameters being checked.

#4. Tensile strength: It is tested for the fabric’s durability.

#5. Microscale combustion calorimeter (MCC): This test is performed to check for the performance of the flame retardant fabrics depending on pH. Since different chemicals are used to coat the fabrics and imbibe flame retardancy properties in them, the pH of the fabric can vary largely. The different pH ranges can differentiate in the thermal stability, heat release behaviour, and flame retardancy of the coated fabrics. It has been observed that the coatings at pH7 or pH4 possessed superior flame retardant performance as compared to other pH ranges, with pH 7 being the best which can be attributed to higher coating viscosity at an acidic condition.

#6. Heat source and the performance tests:

Test methods according to the difference in the source of heat for measuring flame retardant performance are categorized as:

1. BS5852:As mentioned in EN 1021, this test method uses eight different heat sources with a cigarette (0), simulated match/butane flame (1) and Crib (5) being the most commonly used. Going up the source scale intensifies the heat compared to its predecessor.
2. BS5867 – (part 2 type B and C): This test is done to determine the fire behaviour of the fabric.

In Type B, ease of ignition is observed even if the flame reached an edge and the burnt debris starts falling. Testing is done before and after laundering up to 12 wash cycles.

In Type C, after flame time and afterglow time are also measured. Testing is done before and after laundering up to 50 wash cycles.

3. BS7176 – 1995:This testing method provides all information as in the above methods, with additional insight by:
   • Water soak procedure:This procedure is BS 5651: 1990 Clause 3 where the fabric is soaked in water and dried before testing since water soaking can largely affect the flame retardant properties of the fabric.
   • Predictive “Worst Case” testing:Here, high resilient foam is used to identify the hazard categories that are directly linked to the source of ignition.
   • Hazard categories:This helps in identifying the categories under which protection can be ensured like protection from flames, fires, arc flashes, etc. Classifications cover low, medium, high and very high hazard categories.
4. BS476 – (part 22):This helps in measuring the spread of flame across the surface.

If these recommended tests are performed and only the fabrics that qualify for being used in the flame retardant workwear are used, the benefits will be reaped at every level of the supply chain; from the manufacturer to the final worker. Worker’s protection is of utmost priority.