How to test that a fabric has Fire Resistant properties? What is a Stoll curve?

Different types of tests for Fabrics

Arc Flash Test Methods

ASTM F1958

It is the standard test method to determine the identity of clothing with electrical arc exposure using a manikin.

The ASTM F1958 test method provides a way to evaluate finished clothing visually, as the F1959 arc rating test uses small samples of fabric, not complete clothing. Under the garments, the manikins do not have thermal sensors, and they do not predict burn injury. This method is used primarily to provide a qualitative performance view, particularly for buttons, zippers, logos, trim, reflective tape, and other garment components or design features beyond the FR fabric itself.

ASTM F1959

It is the standard test method for determining arc thermal performance by an electric arc and related thermal hazards of textile materials for clothing.

ASTM F1959 is the test method used in FR fabrics to calculate quantitative results (arc ratings). Arc ratings are an arc flash measure of the fabric’s thermal protection.

  • The purpose of this test method is to determine how much heat a certain fabric (or fabric system) will block for the wearer from an electrical arc before the second-degree burns.
  • Reported as Arc Thermal Performance Value (commonly abbreviated as ATPV) is the amount of energy blocked by the fabric. The value will be reported as the Energy Breakopen Threshold (Ebt) if the fabric breaks open before the second-degree burns start.
  • The amount of energy blocked by the fabric is reported as Arc Thermal Performance Value (usually abbreviated as ATPV). If the fabric breaks open before the second-degree burns begin, the value will be reported as the Energy Breakopen Threshold (Ebt).
  • ASTM F1959 test results must be reported for all clothing that meets ASTM F1506 or ASTM F1891. In addition, ASTM F1959 is used to determine ASTM F1891 pass / fail criteria.

Flash Fire Test Methods

ASTM F1930

It is the standard test method for assessing Flame-resistant fabric for flash fire simulations using an instrumented mannequin.

ASTM F1930 sets out a standard process for measuring a fabric’s predicted average body burn based on a simulation of laboratory flash fire. It tells us how to test a manikin, but not what to test for. NFPA 2112 sets pass or fail criteria in a 3-second exposure to 50 percent 2nd and 3rd-degree burn.

  • The fabric is sewn into a standard pattern of the coverall. This coverall is 42R size, without multi-layer fabric pocket bags, cuff pockets or other discretionary areas.
  • The coverall is placed on an instrumented mannequin that has on its surface at least 100 thermocouples, excluding hands and feet.
  • In a simulated flash fire environment with controlled heat flux, flame distribution, and duration, sensors measure the performance of single-layer clothing or protective clothing assemblies.
  • The heat transmitted to each sensor on the manikin surface records the burn injury’s location, extent, and severity. The focus is on total 2nd and 3rd-grade burning.
  • The visual and physical changes to the single-layer clothing or protective clothing ensemble are recorded to help understand how to interpret the results of the burn injury.
  • Afterflame is recorded for the duration, but not for the surface area of the body.
  • Only the particular garment or ensemble tested using the specified heat flux, duration, and flame distribution can apply the measurements obtained and observations noted.

The standard is used to measure the response of flame and heat materials, products or assemblies under controlled conditions. Discretion must be exercised while correlating these findings with flame, heat, products or assemblies under actual conditions of a fire.

However, the results of this test can be used as elements of a fire-hazard assessment or a fire-risk assessment that takes into account all factors relevant to a fire-hazard or fire-risk assessment of a specific end-use.

In the latest update of the ASTM F1930 standard in 2017 changes were primarily related to ASTM style in the 2017 edition. However, the most current data has been updated with several charts showing statistical data relating to percentage body burn, collected from multiple tests conducted in different test facilities.

 

Flame-resistant fabric Footwear Test Methods

ASTM F2412

The test methods of ASTM F2412 measure footwear resistance to hazards that can result in worker injury.

These methods can be used in established safety standards to test compliance with minimum performance requirements. The test methods can be used to determine the footwear’s effectiveness in providing any or all of the following protections:

  • Resistance to impacts to eliminate or decrease the severity of the injury caused by foot striking objects, especially in the toes and metatarsal region
  • Reduced electricity buildup from the wearer to the ground
  • Shock absorbance
  • Resistance to puncture and the chain saw resistance
  • Dialectical isolation to reduce the risk of injury when exposed to high voltage.
  • The standard describes the specific methods for conducting the testing for each of the above-mentioned protections, including diagrams of the equipment used (if applicable).

 

What is a Stoll Curve?

The Stoll Curve for Flame-resistant fabric is one of the great determinants for pass / fail criteria across the board and was developed as a basic threshold for burn prediction. Consider the velocity limit of the Stoll Curve.  If a driver texts while driving at a certain speed and wrecks, the driver could be protected by the collision capacity of the car; if the driver texts while driving over a certain speed and wrecks, the driver might not ultimately be protected by the collision capacity of the car.  Overcoming the speed limit does not guarantee damage to the body, and likewise crossing the Stoll Curve does not guarantee to burn.  There are many other factors to consider; in the driving example, the result will be influenced by distractions (such as texting), a police officer preventing the speeder, etc.  Instead, the Stoll Curve identifies a point where more protection to avoid injury should be considered.

The Stoll Curve determines the heat energy (calories) transfer rating based on the transfer time and the heat energy level generated. Ideally, protective clothing and equipment by absorbing heat energy at increased heat fluxes will delay the transfer. Standards determine the energy absorbed in cal / cm2 before the transfer time to human tissue and the result of a predicted crossing of the Stoll Curve criteria.

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