Fire hazard testingPart 1-21: Guidance for assessing the fire hazard of electrotechnical products — Ignitability — Summary and relevance of test methods BSI Standards Publication... NORM
General
This summary is not a substitute for published standards, which are the only valid reference documents It reflects the current state of test methods and includes relevant observations on their application The list of test methods is not exhaustive, and those not developed by the IEC are not endorsed unless explicitly stated For general guidance on ignitability, refer to IEC 60695-1-20.
Some test methods are material tests and some are end product tests Table A.1 lists the test methods described below and distinguishes between material tests and end product tests
When fire tests are not yet defined and require development or modification for a specific IEC technical committee purpose, collaboration with IEC Technical Committee 89 is essential.
The test method(s) selected shall be relevant to the fire scenario of concern
NOTE 1 Not all the following test methods are specifically ignition or ignitability tests, but some tests have been included because ignition data are, or can be, measured
NOTE 2 Where no repeatability and reproducibility data are known to be available, information may be available from the author/publisher of the relevant test method.
Tests using heated air or electrical heating
Determination of ignition temperature using a hot-air furnace, ISO 871
ISO 871 specifies a laboratory method for determining the flash-ignition temperature and spontaneous-ignition temperature of plastics using a hot-air furnace
A sample of the material is heated in a hot-air ignition furnace at different temperatures to determine the flash-ignition temperature, which is measured using a small pilot flame aimed at the furnace's opening to ignite the released gases In contrast, the spontaneous-ignition temperature is assessed similarly but without the use of an ignition flame.
Materials supplied in any form, including composites, may be used A 3 g sample is used if the density is greater than 100 kg⋅m -3 For cellular materials having a density less than
100 kg⋅m -3 , any outer skin is removed and a block of dimensions 20 mm × 20 mm × 50 mm is cut
An air velocity of 25 mm⋅s -1 is set and an initial test temperature is chosen At the end of
The ignition temperature is determined by adjusting the temperature by 50 °C over a 10-minute period, depending on whether ignition occurs Testing begins 10 °C below the highest temperature in the identified range and continues in 10 °C increments until a temperature is found where ignition does not occur within 10 minutes The ignition temperature is then recorded as the lowest temperature at which ignition is observed.
Data are available in Annex A of ISO 871:2006
This method provides valuable tests for comparing the ignition characteristics of various materials The results indicate the lowest ambient air temperature that can ignite the material under the test conditions These values are anticipated to rank materials based on their susceptibility to ignition in real-world scenarios.
Differential scanning calorimetry (DSC), ISO 11357 [1]
Differential scanning calorimetry (DSC) is a thermal analysis technique that, while not directly measuring ignition, assesses various properties influencing ignitability This method is valuable in fire safety engineering studies and fire modeling.
NOTE Other useful techniques include thermogravimetric analysis (TGA), differential thermal analysis (DTA), thermomechanical analysis (TMA), dynamic mechanical thermal analysis (DMTA), and pyrolysis gas chromatography [2], [3]
ISO 11357 is a comprehensive standard divided into seven parts, detailing methods that utilize Differential Scanning Calorimetry (DSC) to assess various properties of polymeric materials, including thermoplastics, thermosetting plastics, molded materials, and composite materials.
• Temperature and enthalpy of melting and crystallization
• Polymerization temperatures and/or times and polymerization kinetics
1 Numbers in square brackets refer to the bibliography
The Differential Scanning Calorimetry (DSC) method measures the heat flow difference between a test specimen and a reference specimen as temperature and time vary, while both specimens undergo a controlled temperature program in a specified atmosphere.
Test specimens can be either liquid or solid, with an optimal mass typically ranging from 5 mg to 50 mg, depending on the parameter under investigation These specimens are placed in a sample pan, which may be sealed with a lid if necessary The reference specimen is generally an identical empty sample pan.
The instrument undergoes initial calibration before inserting the sample pans, followed by programming the desired thermal cycle Control operations and data analysis are conducted in accordance with the manufacturer's guidelines.
Data are given in annexes to the various parts of ISO 11357
Differential Scanning Calorimetry (DSC) is essential for measuring two key parameters in ignition fire models: the specific heat capacity as a function of temperature and the heat of gasification.
Tests using radiant heat
Heat release rate – Cone calorimeter method, ISO 5660-1 [4]
ISO 5660-1 outlines a standardized method for evaluating the heat release rate, smoke production rate, and mass loss rate of a horizontally oriented test specimen subjected to controlled irradiance levels ranging from 0 kW × m⁻² to 100 kW × m⁻², with a spark ignition source present The heat release rate is calculated by measuring oxygen consumption based on oxygen concentration and flow rate in the combustion product stream Additionally, the time to ignition, indicating sustained flaming, is recorded during the test, while the test specimen is placed on a load cell to monitor mass changes throughout the experiment.
The test method relies on the principle that the net heat of combustion is directly proportional to the oxygen consumed during the process Specifically, it is observed that approximately 13.1 kJ of heat is released for every gram of oxygen utilized in combustion.
The test specimen measures 100 mm by 100 mm and has a thickness of no more than 50 mm It is wrapped in aluminum foil, covering the bottom and sides while leaving the top surface exposed The wrapped specimen is then positioned within a retainer frame, and a substrate is utilized if necessary.
The apparatus is calibrated before setting the exhaust flow and irradiance levels The test specimen is positioned under a radiation shield, and the test commences once the shield is removed and the spark igniter is activated.
Data are collected for typically 32 min after sustained flaming has occurred Three specimens are tested
Data are available in Annex B of ISO 5660-1:2015
Heat release rate is one of the most important variables in determining the hazard from a fire
In a typical fire scenario, various items with multiple surfaces play a significant role in fire development, complicating the evaluation process It is essential to determine the ignition point of each individual surface, if it ignites at all, and this can be achieved through a bench scale test that provides crucial information.
To assess the impact of a fire on nearby items, it is essential to determine the size of the flames from burning materials and evaluate the flame spread across surfaces By understanding the heat release rate per unit area in relation to irradiance over time, as established through bench scale testing, we can calculate the total heat output This total fire output is obtained by summing the contributions from all surfaces and materials involved.
Ignition time data as a function of irradiance can also be used to calculate useful ignition related parameters such as the thermal inertia of materials.
Heat release of insulating liquids, IEC TS 60695-8-3 [5]
This technical specification outlines the test methods for assessing heat release and smoke production from insulating liquids used in electrotechnical products under a specified heat flux Additionally, it may be relevant for evaluating other types of liquid specimens.
The method's principle aligns with the description in section 4.2.1.1, incorporating a laser that measures smoke production by shining through the exhaust effluent, as outlined in ISO 5660-1.
For preliminary tests, 20 cm³ of liquid is utilized, while the main tests require 50 cm³ The liquid is contained in a square stainless steel sample holder measuring 100 mm by 100 mm and 15 mm in depth.
The apparatus is calibrated following ISO 5660-1 standards, and preliminary tests determine the minimum heat flux, known as the critical ignition flux, required for the test specimen to ignite in under 1,200 seconds Subsequent main tests are conducted at this critical ignition flux, with data analysis also adhering to ISO 5660-1 guidelines.
No data are currently available
This test provides a quantitative evaluation of the ignition ease or difficulty of liquids used in electrotechnical applications It also yields data on heat release and smoke production, which are essential for fire safety engineering studies, including fire hazard assessments.
Standard test method for determining material ignition and flame
ASTM E 1321 evaluates the material properties associated with piloted ignition of vertically oriented samples subjected to a consistent heat flux, as well as the lateral flame spread on vertical surfaces caused by externally applied radiant heat.
Test specimens are tested in the form of intended use For the ignition test, specimens are
The flame spread test utilizes specimens measuring 800 mm × 155 mm, while the standard dimensions for testing materials and composites are 155 mm × 155 mm Both tests are conducted on materials with a normal thickness of 50 mm or less, using their full thickness It is important to note that the test method is applicable only to thermally thick specimens, ensuring that when the exposed surface ignites, the back surface remains at a temperature close to the ambient level.
The test method includes two procedures: one for measuring ignition and another for assessing lateral flame spread Specimens are positioned vertically and subjected to heat from a vertical air/gas fueled radiant-heat energy source, which is inclined at 15° to the test specimen.
The ignition test involves exposing a test specimen to a heat flux of 30 kW⋅m\(^{-2}\) and recording the ignition time, if it occurs within 20 minutes This process is repeated until the minimum ignition flux is established, with a tolerance of ± 2 kW⋅m\(^{-2}\) Subsequently, tests are conducted at higher heat fluxes in increments of approximately 10 kW⋅m\(^{-2}\) to create an ignition time versus heat flux profile, covering the range from the minimum ignition flux to 65 kW⋅m\(^{-2}\) The collected data is then correlated with established ignition theories to derive the flammability properties of the material.
In the flame spread test, a specimen is subjected to a heat flux approximately 5 kW⋅m\(^{-2}\) above the minimum ignition threshold, as established by the ignition test The specimen is preheated to thermal equilibrium, with the preheat duration also determined from the ignition test Following ignition, the progression of the flame front along the specimen's horizontal length is monitored over time, and the collected data is analyzed in relation to established theories of ignition and flame spread to derive the material's flammability properties.
No data are currently available
This test method yields essential data, including the minimum surface flux and temperature required for ignition and lateral spread, an effective thermal inertia value, and a flame-heating parameter relevant to lateral flame spread These results are valuable for predicting ignition time and the speed of lateral flame spread on vertical surfaces under specific external flux conditions, without the influence of forced lateral airflow The data can be effectively utilized in fire growth models.
Determination of the characteristic heat flux for ignition from a non-
IEC TS 60695-11-11 outlines a testing procedure to determine the ignition characteristic heat flux (ICHF) of electrotechnical products, sub-assemblies, and materials This method utilizes a non-contacting flame to generate heat flux and assesses the ignition time based on the level of incident heat flux.
Test specimens are derived from a representative sample of the end product material If this is not feasible, specimens are created using the same fabrication process and thickness typically employed in production Each test specimen measures 75 mm ± 1 mm in length and width, applicable for both end-product and materials testing The preferred thicknesses for these specimens are 0.75 mm ± 0.1 mm, 1.5 mm ± 0.1 mm, and 3.0 mm ± 0.2 mm.
To begin, a heat flux meter is utilized to measure the incident heat fluxes at various vertical distances above the flame, which range from 30 kW⋅m\(^{-2}\).
Tests are then carried out on test specimens at heat flux levels which are a multiple of
5 kW⋅m -2 and which are in the range 30 kW⋅m -2 to 75 kW⋅m -2 , such that one of the heat fluxes is the highest at which the average ignition time is greater than 120 s
For the purposes of this test method, ignition of the test specimen is considered to be a sustained and continuous flaming combustion for at least 5 s
Inter-laboratory trials (round-robin tests) have been conducted and the results will be included in the next edition of IEC TS 60695-11-11
This test method evaluates the fire behavior of products, assemblies, and materials when exposed to a nearby flame source, without direct contact An example of this scenario is a candle flame positioned close to an electrotechnical product.
This test method effectively assesses the ignition potential of electrotechnical products when subjected to heat flux from an indirect energy source.
Oxygen index tests
Oxygen index – Ambient temperature test, ISO 4589-2 [8]
ISO 4589-2 measures the minimum volume fraction of oxygen in a nitrogen mixture that can sustain combustion in small vertical test specimens under specific conditions The findings are expressed as percentages known as oxygen index values.
For moulded materials, the test specimens should measure between 80 mm and 150 mm in length, 10 mm in width, and 4 mm in thickness Detailed dimensions for other materials can be found in Table 2 of ISO 4589-2:1996.
A vertical test specimen is placed in an upward-flowing mixture of oxygen and nitrogen within a transparent chimney The specimen's upper end is ignited, allowing observation of its burning behavior to assess the duration of combustion and the length of material consumed against established criteria By conducting tests on various specimens with differing oxygen concentrations, the minimum oxygen level necessary for the desired burning behavior is determined.
Data are given in 9.4 and Annex D of ISO 4589-2:1996
The oxygen index (OI) test at ambient temperature was first described by Fenimore and Martin [9] in 1966 The first use of the method in standards was ASTM Standard Test Method
The D 2863:1970 standard has been widely adopted in various national and international standards, including its publication as ISO 4589 in 1984, which has since been revised to ISO 4589-2 Additionally, the OI test conducted at elevated temperatures is detailed in ISO 4589-3.
Since the establishment of ASTM D 2863 as a standard, numerous studies have been published regarding this test A notable review by Weil, Hirschler, et al highlights the lack of correlation between ASTM D 2863 results and other fire tests, as well as their relevance to actual fire behavior The review concludes that the findings from this test do not align well with any other fire testing methods or the dynamics observed in real fires.
The guidance document, ISO 4589-1 [12] states:
The test serves as a quality control measure for materials, specifically assessing the presence of flame retardants However, it is important to note that this test alone is inadequate for evaluating burning behavior and should not be relied upon for safety regulations or consumer protection standards.
It also states, referring to both ISO 4589-2 and ISO 4589-3:
Small-scale laboratory tests should be viewed strictly as material tests, serving mainly to aid in development, ensure consistency, and assist in the pre-selection of materials They should not be relied upon as the only method for evaluating the potential fire hazard of a material in practical applications.
Oxygen index – Elevated temperature test, ISO 4589-3 [10]
ISO 4589-3 measures the minimum oxygen volume fraction in a nitrogen mixture that can sustain combustion of small vertical test specimens under specific conditions, typically at temperatures ranging from 25 °C to 150 °C The findings, expressed as percentages, represent the oxygen index values at the test temperature, reflecting the conditions that plastic materials may encounter in overheated service scenarios.
The standard outlines a procedure for measuring the temperature at which the oxygen index of small vertical test specimens in air reaches 20.9 under specific testing conditions This temperature is referred to as the flammability temperature (FT), and the method is applicable for results below 400 °C.
For moulded materials, the test specimens should measure between 80 mm and 150 mm in length, 10 mm in width, and 4 mm in thickness Detailed dimensions for other materials can be found in Table 2 of ISO 4589-2:1996.
A vertical test specimen is placed in a transparent double-walled chimney where a mixture of oxygen and nitrogen flows upwards The chimney features a heating element and a pre-heater to ensure the test atmosphere around the specimen maintains the desired temperature The specimen is ignited at its upper end, and its burning behavior is observed to assess the duration of burning or the length of the specimen consumed, comparing these results to established limits By conducting tests with various oxygen concentrations, the minimum oxygen level necessary for the desired burning behavior at the specified temperature is determined.
Annex A of ISO 4589-3:1996 outlines an alternative method for measuring flammability temperature (FT) In this method, air is directed upwards through a chimney at a predetermined test temperature, while the burning behavior of the specimen is observed Based on the initial observations, subsequent tests are conducted at adjusted temperatures, either higher or lower This process continues until the FT is determined, within a 5 °C increment, as the lowest temperature at which the specimen meets at least one of the specified test criteria.
Currently, there is no available repeatability data Annex B of ISO 4589-3:1996 provides a summary of interlaboratory results from a correlation exercise conducted in the UK in 1986, aimed at evaluating the impact of various specimen support types, which can be used to calculate reproducibility data This exercise involved the participation of eight laboratories.
The flammability temperature test establishes a pass/fail criterion at a specific temperature, commonly used to demonstrate acceptable behavior at a limiting temperature This method is appropriate only for well-characterized material grades Caution is essential when testing unknown compounds, as satisfactory behavior observed above the flammability temperature may be misleading Flammable volatiles could be expelled from the chimney during the conditioning period before ignition attempts, potentially making the tested material less flammable than the original.
Some flame-retarded materials may be inaccurately represented by testing methods If the flame retardant functions by releasing gas phase combustion inhibitors, such as water vapor, carbon dioxide, and antimony halides/oxyhalides, during pyrolysis, these inhibitors could be expelled from the chimney during the conditioning phase before ignition This process may cause the tested material to appear more flammable than the original, untreated material.
Glowing/hot-wire based test methods
Glow wire tests, IEC 60695-2-11 [14], IEC 60695-2-12 [15] and
4.5.1.1 Glow-wire flammability test for end-products, IEC 60695-2-11 [14]
The glow-wire is a specified loop of resistance wire, which is electrically heated to a specified temperature The test apparatus is described in IEC 60695-2-10 [13]
IEC 60695-2-11 aims to prevent ignition of components under specified conditions, ensuring that if a part does ignite, it burns for a limited time without spreading flames or releasing burning or glowing particles.
The test specimen should be a complete end-product chosen so that the conditions of the test will not be significantly different from those occurring in normal use
If testing on a complete end-product is not feasible, it is permissible to either extract a section containing the part being examined, create an opening in the end-product for glow-wire access, or completely remove the part for separate testing.
The heated glow-wire tip is applied to a test specimen for a designated duration, during which various observations and measurements are conducted according to the specific testing protocol.
The tip of the glow-wire is applied horizontally to the part of the test specimen which is likely to be subjected to thermal stresses in normal use
No data are known to be available
This test establishes a pass/fail criterion at a temperature determined by the relevant product committee Electrotechnical committees primarily use this test to verify the suitability of insulating materials in contact with live parts or electrical connections that may overheat due to faults The objective is to prevent the ignition of insulating materials, thereby avoiding the risk of fire spreading from the product.
Overheating in electrical connections can lead to ignition; however, once the fault current is removed, a tested insulating material is expected to self-extinguish Consequently, while the product may become unusable, the risk of flame spread is minimal, ensuring that users and surrounding property remain safe from fire hazards.
This test has been used for many years as an alternative/replacement for IEC 60695-2-3,
Bad connection test, which was withdrawn in 2003
As well as checking the integrity of the supporting insulating material, during the test, the operator also records whether flaming or molten droplets fall onto a specified surface below
To evaluate a large product's performance, a sample of the material typically exposed to droplets is placed beneath the test specimen If this protective layer remains undamaged and retains the molten material, the outcome is deemed satisfactory In cases where there is no surface to contain the droplets, such as when they may escape onto a flammable surface, a standard sheet of wrapping tissue is utilized on a wooden board for testing.
The operator documents the ignition status of the material, with some product committees noting instances of ignition and establishing a standardized zone above the live part or electrical connection for additional testing This process, referred to as consequential testing, may involve the needle flame test (see 4.6.1).
4.5.1.2 Glow-wire flammability index (GWFI) test method for materials,
The glow-wire is a specified loop of resistance wire, which is electrically heated to a specified temperature The test apparatus is described in IEC 60695-2-10 [13]
IEC 60695-2-12 aims to establish the glow-wire flammability index (GWFI) for solid electrical insulating materials and other solid substances The GWFI represents the maximum temperature at which three test specimens meet the defined criteria.
Test specimens should have dimensions of at least 60 mm × 60 mm, with a preferred thickness These specimens can be produced through various methods, including compression moulding, injection moulding, casting, or by cutting from sheets or components of finished products.
The heated glow-wire tip is applied to the vertically positioned test specimen for a designated duration, during which various observations and measurements are recorded according to the specific testing protocol.
By repeated tests with different test temperatures of the glow-wire, using a new test specimen each time, the GWFI of the material under test is established
No data are known to be available
This materials test involves standard test specimens and provides data for a preselection process to evaluate materials against IEC 60695-2-11, the glow-wire flammability test method for end products However, it is important to note that this test method does not assess the flammability, fire behavior, or fire hazard of complete equipment, as factors such as the dimensions of insulating systems, combustible parts, and heat transfer to adjacent materials significantly affect the flammability of the materials used.
As an outcome of conducting a fire hazard assessment, an appropriate series of preselection flammability and ignition tests may permit reduced end product testing (see IEC 60695-1-30)
4.5.1.3 Glow-wire ignition temperature (GWIT) test method for materials,
The glow-wire is a specified loop of resistance wire, which is electrically heated to a specified temperature The test apparatus is described in IEC 60695-2-10 [13]
IEC 60695-2-13 aims to establish the glow-wire ignitability index (GWIT) for solid electrical insulating materials and other solid substances The GWIT represents the minimum temperature required for ignition to occur.
Test specimens should have dimensions of at least 60 mm × 60 mm, with a preferred thickness These specimens can be produced through various methods, including compression moulding, injection moulding, casting, or by cutting from sheets or components of finished products.
The heated glow-wire tip is applied to the vertically positioned test specimen for a designated duration, during which various observations and measurements are conducted according to the specific testing protocol.
By repeated tests with different test temperatures of the glow-wire, using a new test specimen each time, the GWIT of the material under test is established
No data are known to be available
This materials test evaluates standard test specimens to gather data for a preselection process, assessing materials against the IEC 60695-2-11 glow-wire flammability test method for end products However, this test method is not suitable for determining the ignitability, fire behavior, or fire hazard of complete equipment, as factors such as the dimensions of insulating systems, combustible parts, design, and heat transfer to adjacent materials significantly affect the flammability of the materials involved.
As an outcome of conducting a fire hazard assessment, an appropriate series of preselection flammability and ignition tests may permit reduced end product testing (see IEC 60695-1-30)
4.5.2 Hot wire coil ignitability test, IEC 60695-2-20 3 and ASTM D 3874 [17]
Hot wire coil ignitability test, IEC 60695-2-20 and ASTM D 3874 [17]
The test specimen consists of a bar specimen measuring 125 mm ± 5 mm by 13,0 mm ± 0,5 mm at the thickness to be evaluated
In this test method, a specimen is horizontally supported at both ends, with its center wrapped in a coil of heater wire When a fixed power density is applied to the heater wire, it heats rapidly The test observes the specimen's behavior until one of three outcomes occurs: ignition of the material, melting of the material, or the completion of 120 seconds of exposure without ignition or melting The times to ignition and melt-through are recorded as applicable.
There are currently no published data available ASTM D 3874 states:
When following this test method carefully, the average result is expected to be within ±15% of the value obtained from an interlaboratory evaluation.
However, the IEC test was withdrawn in 2007 because of unsatisfactory repeatability and reproducibility
This test method is essential for the preselection of materials, quality control, and product evaluation The data obtained are crucial for assessing the suitability of polymeric materials used in electrical equipment that may come into direct contact with or be within 0.8 mm of potential ignition sources.
Flame tests
Needle flame test, IEC 60695-11-5 [18]
The needle flame test, IEC 60695-11-5, simulates the effect of a small flame which may result from fault conditions, in order to assess the fire hazard
The test specimen is a complete equipment, sub-assembly or component
A 12 mm high butane test flame is directed at the area of the test specimen most susceptible to flames for a designated time Beneath the test specimen, a specific layer is positioned to assess the potential for fire spread Observations are made during and after the flame application for any glowing, dripping particles, and signs of ignition.
No data are known to be available
The needle flame test evaluates the suitability of materials potentially impacted by flames from insulating materials near live electrical components during overheating conditions Additionally, it serves to assess materials that may necessitate further testing.
In instances where a component typically required to comply with IEC 60695-2-11 has dimensions that are not compatible with the glow wire test apparatus, product committees may opt to utilize the needle flame test outlined in IEC 60695-11-5.
4.6.2 50 W horizontal and vertical flame test methods, IEC 60695-11-10 [19]; 500 W flame test methods, IEC 60695-11-20 [20]
IEC 60695-11-10 is a test method using a 50 W flame IEC 60695-11-20 is a test method using a 500 W flame
These test methods evaluate solid electrical insulating materials, offering an initial assessment of their response to flame ignition sources The results enable the verification of material characteristics' consistency and indicate advancements in insulating material development, facilitating a comparative classification of different materials.
In both test methods the test specimen is 125 mm long, 13 mm wide, and up to 13 mm thick
These tests involve applying a flame ignition source to a horizontal or vertical test specimen and measuring the burned length or surface spread of flame rate
NOTE The apparatus for producing the 50 W flame is described in IEC 60695-11-4 [21] The apparatus for producing the 500 W flame is described in IEC 60695-11-3 [22]
Data are available in IEC 60695-11-10:2013, Annexes A and B, and IEC 60695-11-20:2015, Annex A
This materials test evaluates standard test specimens to gather data for assessing materials' compliance with flammability requirements for end products However, it is important to note that this test method does not accurately determine the flammability, fire behavior, or fire hazard of complete equipment items, as factors such as the dimensions of insulating systems, combustible components, design, and heat transfer to surrounding materials significantly affect flammability.
As an outcome of conducting a fire hazard assessment, an appropriate series of preselection flammability and ignition tests may permit reduced end product testing (see IEC 60695-1-30)
4.6.3 1 kW nominal pre-mixed flame, IEC 60695-11-2 [23]
IEC 60695-11-2 provides detailed requirements for the production of a 1 kW nominal, propane based pre-mixed type test flame
The test flame is utilized for evaluating electrotechnical equipment, sub-assemblies, components, and solid electrical insulating materials, as well as other combustible materials Detailed specifications for test specimens are outlined in the applicable standards that incorporate this test flame.
Examples of appropriate test arrangements are given in Annex B of IEC 60695-11-2:2013 Numerous tests use this flame ignition source For details the relevant test method should be consulted
For testing equipment, it is generally recommended to maintain a distance of approximately 100 mm from the top of the burner tube to the surface of the test specimen, unless specified otherwise Additionally, the burner should remain fixed in position throughout the test.
For testing material strips, the operator should position the tip of the blue cone in the flame close to the test specimen without making contact, allowing for adjustments as the specimen distorts or burns.
4.6.3.4 Confirmation of the test flame
Confirmation of the test flame is carried out by measuring the time taken for a defined copper block to increase in temperature by a defined amount
This 1 kW, high intensity, pre-mixed test flame is very widely used to simulate the reaction to fire of end-products, components and materials to the direct impingement of a flame ignition source.
Vertical and 60 ° tests for aircraft components, FAR 25 [25]
According to FAR 25.869 (a), electrical system components must meet specific requirements, including that the insulation on electrical wires and cables within an aircraft fuselage must be self-extinguishing This requirement is verified through a 60 ° Bunsen burner test outlined in Part I, Appendix F of FAR 25.
According to FAR 25.853, materials and components utilized in crew and passenger compartments must meet specific requirements Notably, it mandates that electrical conduits must be self-extinguishing, as verified by the vertical Bunsen burner test outlined in Part I, Appendix F of FAR 25.
The vertical Bunsen burner test requires a test specimen that is a minimum of 50 mm wide and 305 mm long, unless a smaller size is utilized in the airline Additionally, the thickness of the test specimen must not exceed the minimum thickness that is qualified for use in an airline.
The test specimen for the 60 ° Bunsen burner test is a length of wire or cable The gauge is the same as that used in the airline
These tests involve applying an ignition source to a 60 ° or vertical test specimen The flame time, burned length, and flaming time of drippings, if any, are then measured or noted
Electrical conduits are submitted to a 12 s application of flame Wire and cable products are submitted to a 30 s application of flame
No data are known to be available
These test methods are used for the preselection of materials, quality control and product evaluation for electrical wires, electrical cables and electrical conduit used in the aviation industry.
Tests using an electrical arc
Tracking index tests, IEC 60112 [26], ASTM D 3638 [27]
IEC 60112 and ASTM D 3638 outline testing methods for determining the comparative tracking index (CTI) of solid insulating materials, utilizing alternating voltages on equipment parts and material plaques Additionally, IEC 60112 includes procedures for assessing the proof tracking index (PTI) and allows for erosion evaluation when necessary For a summary of the key differences between IEC 60112 and ASTM D 3638, refer to Table 1.
The IEC 60112 test method requires that the test specimen be flat, with a minimum thickness of 3 mm and a sufficient area to prevent liquid from flowing over its edges during testing It is recommended that the specimen size be at least 20 mm × 20 mm.
According to ASTM D 3638, a minimum thickness of 2.5 mm is required If thinner samples are utilized, they must be stacked to meet the minimum thickness specified in both test standards.
The test specimen's upper surface is held in a nearly horizontal position and exposed to electrical stress through two platinum electrodes spaced 4 mm apart, utilizing an alternating current voltage ranging from 100 V to 600 V During the test, electrolyte drops are applied between the electrodes until either an over-current device activates, ignition and a continuous flame are observed, or the designated test duration concludes.
The individual tests are of short duration (less than 1 h) with up to 50 or 100 drops of about
20 mg of electrolyte falling at 30 s intervals The number of drops needed to cause failure usually increases with decreasing applied voltage and, below a critical value, tracking ceases to occur
During the test, the specimen may also erode or soften, thereby allowing the electrodes to penetrate it If required, erosion is measured If a hole is formed, this is reported
Table 1 lists the main differences between IEC 60112 and ASTM D 3638
Table 1 – Main differences between IEC 60112 and ASTM D 3638
Ammonium chloride and alkyl naphthalene sulphonate (aq.)
Length of the electrodes ≥ 12 mm ≥ 20 mm
Evaluation of test results for
The maximum voltage that does not cause ignition or tracking (conduction) with solution
A a) 5 test specimens withstand 50 drops without failure, and b) 5 test specimens withstand 100 drops at
25 V lower Result reported e.g as: “CTI 300”
If the voltage, at which 100 drops can be applied without failure, is lower than the CTI – 25 V, then that voltage is written in parentheses along with the CTI value
The voltage which will cause failure by tracking (conduction) when the number of drops of contaminant required to cause failure is equal to 50
Ignition of the specimen is not a failure criterion
The test is done on 5 specimens
The average number of drops/voltage relation is plotted on a graph
The CTI voltage is read from the graph where 50 drops cause failure
Evaluation of test results for
CTI-M The same as for CTI, but with solution B Not applicable
Evaluation of test results for
The same as for CTI part a)
It is used as a pass or fail test at a voltage specified in an end product specification
For IEC 60112 data are reported in IEC TR 62062:2002 [28]
The test discriminates between materials with relatively poor resistance to tracking, and those with moderate or good resistance, for use in equipment which can be used under moist conditions
The test fails to effectively indicate a material's resistance to ignition from an arcing source as a primary failure mode It is designed to simulate accelerated conditions for evaluating tracking, but these do not accurately represent real-world conditions where arc ignition may happen Although ignition of the specimen frequently occurs during the test, it is merely a secondary event following the formation of a carbon track.
More rigorous and extended testing is essential for evaluating the performance of materials intended for outdoor applications This involves using higher voltages and larger test specimens, as outlined in the inclined plane test according to IEC 60587 [29].
High-Current Arc Ignition (HAI), UL 746A – Sec 32 [30]
UL 746A – Sec 32 establishes criteria to evaluate the ignition resistance of solid insulating materials when exposed to arcing electrical sources During both normal and abnormal operations of electrical equipment, these insulating materials can be near arcing sources, and if the arcing is intense or prolonged, it poses a risk of ignition.
The test specimen consists of a bar sample measuring 125 mm ± 5 mm by 13,0 mm ± 0,5 mm at the thickness to be evaluated
In a test setup, a copper rod and a stainless steel rod, both positioned at a 45º angle to the horizontal, make contact with a test specimen The stainless steel electrode can be moved away to break the arc and then returned to reestablish it, creating a cyclic motion along its 45º axis The test begins with a 32.5 A circuit (power factor 0.5) activated, and the movable electrode cycles at 40 arcs per minute until a flame is detected or the specimen endures 200 arcs without ignition Additionally, the test can be conducted with the initial electrode contact set at either 1.6 mm or 3.2 mm above the surface.
Currently, there is a lack of published data, but several factors are known to cause significant deviations in measured data These include variable arc profiles resulting from the asynchronous timing of AC frequency and arc initiation, the deterioration of electrode tips during testing, and insufficient control over the movable electrode.
A revised method that addresses these issues (and others) is currently under development in the United States
Test methods are essential for preselecting materials, ensuring quality control, and evaluating products The data obtained from these tests help assess the suitability of polymeric materials for electrical equipment, particularly when they are in close proximity to non-arcing sources (within 0.8 mm) or arcing sources (within 12.7 mm).
High-voltage arc resistance to ignition (HVAR), UL 746A – Sec 33 [31]
UL746A – Sec 33 classifies solid insulating materials based on their resistance to ignition and the development of a visible carbonized conducting path on their surface This assessment is crucial when these materials are exposed to high voltage, low current arcing, which can occur during the malfunction of specific high voltage power supplies in electrical equipment.
The test specimen consists of a bar sample measuring 125 mm ± 5 mm by 13,0 mm ± 0,5 mm at the thickness to be evaluated The test specimens are preconditioned for a minimum of
40 h at 23 ºC ± 2 ºC and at 50 % ± 5 % relative humidity
Two electrodes are positioned at a 45º angle to the horizontal, with a separation of 4.0 mm ± 0.1 mm on the test specimen's surface The test begins with an initial circuit of 5.2 kV and a current limiter set to 2.36 mA, generating a continuous arc between the electrodes The duration of the test is either 5 minutes or until ignition or a hole develops in the specimen.
No data are currently available
These testing methods are essential for preselecting materials, ensuring quality control, and evaluating products The data obtained is valuable for assessing the appropriateness of polymeric materials used in electrical equipment, particularly when they are in direct contact or near uninsulated live components, with specific distances of 0.8 mm for non-arcing and 12.7 mm for arcing situations.
Annex A provides an informative overview of the applicability of various test methods, distinguishing between material tests and end-product tests Table A.1 outlines these methods, including the hot-air furnace test (ISO 871), which measures the flash-ignition and spontaneous-ignition temperatures of plastics, and differential scanning calorimetry (ISO 11357), assessing properties affecting ignitability The cone calorimeter method (ISO 5660-1) primarily evaluates heat release rates, while the heat release of insulating liquids (IEC 60695-8-3) tests both heat release rates and ignition times Additionally, the material ignition and flame spread test (ASTM E 1321) is used for assessing interior building materials, and the ICHF from a flame source (IEC/TS 60695-11-11) measures ignition time based on heat flux The oxygen index tests (ISO 4589-2 and ISO 4589-3) determine whether burning is sustained after ignition at ambient and elevated temperatures, respectively Lastly, the glow-wire flammability test for end-products (IEC 60695-2-11) uses a hot wire as an ignition source.
The glow-wire flammability test for materials, outlined in IEC 60695-2-12, utilizes a hot wire ignition source applied for 30 seconds to determine the glow-wire flammability index (GWFI) Similarly, the glow-wire ignitability test, specified in IEC 60695-2-13, also employs a hot wire for 30 seconds to assess the glow-wire ignitability index (GWIT) The hot wire coil ignitability test, referenced in ASTM D 3874 (IEC 60695-2-20, withdrawn), involves a hot wire coiled around the test specimen with heating applied for up to 120 seconds; however, this IEC test method was withdrawn due to issues with repeatability and reproducibility Additionally, the needle flame test, according to IEC 60695-11-5, uses a small diffusion flame as the ignition source.
The article discusses various flame test methods as outlined in IEC 60695 standards It includes a 50 W pre-mixed flame test method (IEC 60695-11-10) and a 500 W pre-mixed flame test method (IEC 60695-11-20) Additionally, it covers a nominal 1 kW pre-mixed flame test (IEC 60695-11-2) The document also references vertical and 60° tests for aircraft components as specified in FAR 25 – Part I – Appendix F, which focuses on testing aerospace electrical wires and cables.
The comparative tracking indices of solid insulating materials are evaluated according to IEC 60112, where ignition that causes persistent flaming (burning for more than 2 seconds) is considered a failure criterion The standard test method for the comparative tracking index of electrical insulating materials is ASTM D 3638, which also requires reporting of flame ignition Additionally, the high-current arc ignition (HAI) test outlined in UL 746A, Section 32, is utilized to assess polymeric insulating materials, while the high-voltage arc ignition (HVAR) test in UL 746A, Section 33, serves a similar purpose for evaluating these materials.
C TI = C om par ati ve tr ac ki ng i ndex b
P TI = P roof tr ac ki ng i ndex
[1] ISO 11357, Plastics – Differential scanning calorimetry (DSC)
[2] SFPE Handbook of Fire Protection Engineering, National Fire Protection Association
Press, Quincy, MA (USA), 1995, pp 1-103 to 1-106
[3] Haines, P J., Thermal methods of analysis, Blackie Academic & Professional,
[4] ISO 5660-1:2015, Reaction-to-fire tests – Heat release, smoke production and mass loss rate – Part 1: Heat release rate (cone calorimeter method)
[5] IEC TS 60695-8-3, Fire hazard testing – Part 8-3:Heat release – Heat release of insulating liquids used in electrotechnical products
[6] ASTM E 1321, Standard Test Method for Determining Material Ignition and Flame
[7] IEC TS 60695-11-11, Fire hazard testing – Part 11-11: Test flames – Determination of the ignition characteristic heat flux from a non-contacting flame source
[8] ISO 4589-2:1996, Plastics – Determination of burning behaviour by oxygen index –
[9] Fenimore and Martin, Modern Plastics, 43, p 141, 1966
[10] ISO 4589-3:1996, Plastics – Determination of burning behaviour by oxygen index –
[11] Weil, Hirschler, Patel, Said and Shakir, Fire and Materials, 16(4), p 159, 1992
[12] ISO 4589-1, Plastics – Determination of burning behaviour by oxygen index – Part 1:
[13] IEC 60695-2-10, Fire hazard testing – Part 2-10: Glowing/hot-wire based test methods
– Glow-wire apparatus and common test procedure
[14] IEC 60695-2-11, Fire hazard testing – Part 2-11: Glowing/hot-wire based test methods
– Glow-wire flammability test method for end-products
[15] IEC 60695-2-12, Fire hazard testing – Part 2-12: Glowing/hot-wire based test methods
– Glow-wire flammability test method for materials
[16] IEC 60695-2-13, Fire hazard testing – Part 2-13: Glowing/hot-wire based test methods
– Glow-wire ignitability test method for materials
[17] ASTM D 3874, Standard Test Method for Ignition of Materials by Hot Wire Sources
[18] IEC 60695-11-5, Fire hazard testing – Part 11-5: Needle flame test
[19] IEC 60695-11-10:2013, Fire hazard testing – Part 11-10: Test flames – 50 W horizontal and vertical flame test method
[20] IEC 60695-11-20:2015, Fire hazard testing – Part 11-20: Test flames – 500 W flame test methods
[21] IEC 60695-11-4, Fire hazard testing – Part 11-4: Test flames – 50 W flame –
Apparatus and confirmational test method
[22] IEC 60695-11-3, Fire hazard testing – Part 11-3: Test flames – 500 W flames –
Apparatus and confirmational test methods
[23] IEC 60695-11-2:2013, Fire hazard testing – Part 11-2: Test flames – 1 kW pre-mixed flame test method
[24] IEC 60695-11-40, Fire hazard testing – Part 11-40: Test flames – Confirmatory tests –
[25] FAR 25, Federal Aviation Regulations – Airworthiness standards – Part 25: Transport category – Airplanes
[26] IEC 60112, Method for the determination of the proof and the comparative tracking indices of solid insulating materials
[27] ASTM D 3638, Standard Test Method for Comparative Tracking Index of Electrical
[28] IEC TR 62062:2002, Results of the Round Robin series of tests to evaluate proposed amendments to IEC 60112
[29] IEC 60587, Test method for evaluating resistance to tracking and erosion of electrical insulating materials used under severe ambient conditions
[30] UL 746A – Sec 32, Standard for Polymeric Materials – Short Term Property
Evaluations – Sec 43: High-current arc ignition test
[31] UL 746A – Sec 33, Standard for Polymeric Materials – Short Term Property
Evaluations – Sec 44: High-voltage arc ignition test
[32] ISO 871:2006, Plastics – Determination of ignition temperature using a hot-air furnace