FIRE HAZARD TESTING – Part 6-2: Smoke obscuration – Summary and relevance of test methods 1 Scope This part of IEC 60695 provides a summary of the test methods that are used in the asse
General
Test methods are characterised by whether they are static or dynamic and/or by the nature of the test specimen.
Physical fire model
The smoke released from a material is not an inherent property but is significantly influenced by the burning conditions Key factors such as decomposition temperature, ventilation levels, and fuel composition play a crucial role in determining the composition of fire effluent, ultimately affecting both the quantity of smoke produced and the rate of smoke generation.
Demonstrating the relevance of test conditions in standardized fire models to real fire stages is essential ISO 19706 provides a general classification of fire stages, as detailed in Table 1 Key factors influencing smoke production include oxygen concentration and irradiance/temperature.
Static test methods
A static smoke test involves allowing smoke to accumulate within a test chamber, which may lead to some re-circulation and secondary combustion of smoke particles Factors such as deposition, agglomeration, stirring, and progressive oxygen depletion can influence the level of obscuration caused by the smoke.
Dynamic test methods
A dynamic smoke test involves a continuous flow of fire effluent through a measuring device without re-circulation, ensuring that smoke particles do not accumulate Instead, these particles are dispersed in a controlled airflow within the test apparatus During this process, the decay of smoke can occur, which may involve the coagulation of particles and their deposition due to cooling.
Table 1 – Characteristics of fire stages (ISO 19706) Fi re st ag es H eat f lu x to fu el su rf ace kW /m 2
The article discusses various combustion scenarios, detailing parameters such as maximum temperature, oxygen volume percentage, and fuel/air equivalence ratios It categorizes combustion into non-flaming, well-ventilated flaming, and under-ventilated flaming types Non-flaming combustion includes self-sustaining smoldering and oxidative or anaerobic pyrolysis, with temperatures ranging from 100 to 800 °C and varying efficiency levels Well-ventilated flaming combustion operates at temperatures between 350 to 650 °C, with a fuel/air equivalence ratio of approximately 20 Under-ventilated flaming combustion is characterized by localized fires in poorly ventilated spaces, with temperatures from 0 to 150 °C and oxygen consumption significantly lower than in well-ventilated conditions The article emphasizes the importance of external radiation sources and room geometry in determining combustion characteristics, as well as the variability of combustion ratios based on material chemistry and thermal conditions.
The test specimen may be a manufactured product, a component of a product, a simulated product (representative of a portion of a manufactured product), a basic material (solid or liquid), or a composite of materials
General
The static test methods discussed here are based on widely recognized international, national, or industry standards commonly used in the electrotechnical field This review does not aim to cover every possible test method available.
NOTE These summaries are intended as a brief outline of the test methods, and should not be used in place of full published standards.
Determination of smoke opacity in a 0,51 m3 chamber
Standards which use a vertically oriented test specimen
Two international and four national standards are based on testing a vertically oriented test specimen in a single chamber of 0,51 m 3 volume
The chamber, commonly known as the "NBS chamber," was developed in the USA by the National Bureau of Standards, which is now called the National Institute of Standards and Technology.
These are: IEC/TR 60695-6-30 [1] 2 and IEC 60695-6-31 [2], ASTM E662 [3], BS 6401 [4],
This small-scale fire test evaluates the smoke opacity produced by a vertically oriented material specimen subjected to specific thermal irradiance in a closed chamber of 0.51 m³, with or without pilot flames The luminous flux passing through the smoke is continuously monitored throughout the test.
The test specimen is a flat piece 76,2 mm × 76,2 mm, with a maximum thickness of 25,4 mm
The method utilizes an electrical radiant energy source to generate a heat flux of 25 kW/m² on a vertically positioned test specimen Testing is conducted in two modes: non-flaming, which relies solely on the radiant energy source, and flaming, where a small burner is added to create pilot flames along the lower edge of the specimen, igniting any combustion products.
A photometric system using polychromatic white light, with a vertical light path is used to measure the variation in light transmission during the test
2 Figures in square brackets refer to the Bibliography
Results are expressed in terms of specific optical density, D S, which is calculated using the following equation:
V is the volume of smoke (i.e the volume of the chamber);
A is the exposed surface area of the test specimen;
L is the path length of the light used to measure the smoke;
I is the incident luminous flux;
T is the transmitted luminous flux
D S is related to the extinction area of the smoke (S) by the equation:
D s = × where S is the extinction area of smoke
NOTE D m is used instead of D s in NF C20-902-1 & -2 (see A.1)
Repeatability and reproducibility have been determined in an interlaboratory trial, based on the French standards NF C20-902-1 and NF C20-902-2
The results, presented in accordance with ISO 5725-2, are given in Annex A
6.2.1.6 Relevance of test data and special observations
Test methods based on the NBS smoke chamber have been in worldwide use since about
Since its introduction in 1970 for material evaluation, the NBS method has been largely replaced by ISO 5659-2 due to several significant limitations Firstly, the NBS method operates at a relatively low heat flux with limited air supply, only replicating conditions found in ISO 19706 fire stages 1b and possibly 2 Secondly, the small, vertically mounted, and flat test specimens restrict the evaluation to materials, excluding liquids and certain thermoplastics Additionally, specimens that swell towards the furnace can cause increased incident heat flux, potentially extinguishing pilot flames and invalidating the test Lastly, the low heat flux and specific geometry of test specimens hinder the establishment of a reliable link between NBS chamber data and other fire scenarios.
The NBS smoke chamber method has several limitations, including a lack of correlation between test data and real fire behavior, no monitoring of specimen mass during testing, and a limited air supply that halts combustion when oxygen levels drop below 14% Additionally, significant smoke deposition on walls occurs, and the method's repeatability and reproducibility are poor, varying with the material tested Materials that exhibit high flow, excessive swelling, or inconsistent ignitability yield less reliable results.
The method does however offer the useful option to evaluate smoke production from both flaming and non-flaming combustion, albeit at a low heat flux
The data generated are not suitable for use as input to fire hazard assessment or for fire safety engineering
This method is not advisable for the development of electrotechnical products and should not serve as a foundation for regulations or controls regarding smoke release in these products, owing to the constraints of the physical fire model and the geometry of the test specimens.
Standard which uses a horizontally oriented test specimen
One International standard, ISO 5659-2 [7], is based on the following method:
This test evaluates the smoke opacity produced by a horizontally positioned material specimen subjected to a defined thermal irradiance, with or without a pilot flame, within a closed chamber of 0.51 m³ The luminous flux passing through the smoke is continuously monitored and documented.
NOTE This method uses essentially the same apparatus as described in 6.2.1, with the exception of modifications to the source of thermal irradiance and test specimen orientation
The test specimen is a flat piece 75 mm × 75 mm with a maximum thickness of 25 mm
This test method utilizes an electrically heated conical radiant energy source to subject horizontally mounted test specimens to incident flux levels of 25 kW/m² or 50 kW/m² The heat source features electrical windings housed within a truncated steel cone, and the exposure can occur in either flaming or non-flaming mode, depending on the presence of a pilot flame from a small gas burner.
The test chamber, with a volume of 0.51 m³, is a sealed environment where smoke opacity is evaluated using a photometric system A vertical white light source illuminates the chamber, and a photodetector quantifies the reduction in light transmission caused by smoke accumulation.
Test specimens are placed horizontally under the conical radiant heater with a distance of
The distance between the surface of the test specimen and the lower edge of the heater should be 25 mm However, for test specimens that intumesce when exposed to the conical radiant heater, this distance must be increased to 50 mm Additionally, the heat flux applied to the test specimen is calibrated beforehand based on the specified distance.
The light transmission measurements are used to determine the specific optical density of smoke
The mass loss of the test specimen can be continuously monitored using a load cell positioned beneath it This method also allows for the determination of the mass optical density of smoke.
Results are expressed in terms of specific optical density 10 min after the start of the test,
D s 10 , which is calculated using the following equation:
V is the volume of smoke (i.e the volume of the chamber);
A is the exposed surface area of the test specimen;
L is the path length of the light used to measure the smoke;
T 10 is the percentage transmittance after 10 min;
D s10 is related to the extinction area of the smoke produced after 10 min, S (t min) , by the equation:
Results can also be expressed in terms of mass optical density, D mass , by the equation:
The relationship between D mass and the extinction area of the smoke is given by:
An interlaboratory trial involving eight laboratories has been carried out during the development of ISO 5659-2 The results, presented in accordance with ISO 5725-2, are given in Table B.1 in Annex B
An interlaboratory trial was conducted with ten laboratories to evaluate two intumescent plastics, polycarbonate and PVC flooring, using a test specimen-heater distance of 50 mm, as part of the revision of ISO 5659-2 The results, formatted according to ISO 5725-2, are detailed in Table B.2 and Table B.3 in Annex B.
6.2.2.6 Relevance of test data and special observations
This method enhances the NBS smoke chamber approach by allowing horizontal orientation of test specimens, making it suitable for evaluating thermoplastics and potentially liquids in the future, although it remains limited to flat specimens The maximum heat flux has been increased to 50 kW/m², enabling the replication of ISO 19706 fire stages 3a), 1b), and 2, which enhances the differentiation of flame retardant materials Additionally, recorded mass loss rate data can be utilized for hazard assessment and calculating mass optical density, contributing valuable information for fire safety engineering Furthermore, a testing method for intumescent materials has been incorporated.
The method's repeatability and reproducibility vary significantly based on the material being tested, with smoke generation being particularly influenced by the ignition behavior of the material.
The International Maritime Organisation (IMO) utilizes this method for regulatory control; however, it is not advisable to apply it for regulating electrotechnical products unless the products in question adhere to specific limitations regarding test specimen geometry.
Determination of smoke density in a 27 m3 smoke chamber
Standards
Four international standards are based on a 27 m 3 (3 m × 3 m × 3 m) smoke chamber These are: IEC 61034-1 [8], IEC 61034-2 [9], EN 61034-1 [10], EN 61034-2 [11] The chamber is often referred to as the “three metre cube”
Two national standards use the “three metre cube” chamber These are BS 6853 [12] and CEI 20-37-3 [13].
Purpose and principle
This test evaluates the smoke density produced by materials or products when subjected to a flame in a closed chamber, with continuous measurement and recording of the luminous flux passing through the smoke.
Test specimen
The test specimen consists of horizontally oriented materials or products, typically 1 m long, positioned above the ignition source.
Method
The test method utilizes a one-liter pan of burning alcohol as the flame source within a closed chamber of 27 m³ Smoke density is assessed using a photometric system that shines white light horizontally across the chamber at a height of 2.15 m A photodetector measures the reduction in light transmission caused by smoke accumulation, allowing for the evaluation of maximum obscuration during the test To ensure uniform smoke distribution and reduce stratification, a fan operates continuously throughout the test.
In some standards, percentage transmittance (% T ) values are recorded, using the following formula:
I is the incident luminous flux;
T is the transmitted luminous flux
In some standards, primarily for cables, optical density values (referred to as A m ) are calculated using the following formula:
NOTE A m is also incorrectly known in some standards as absorbance and results are reported in terms of a parameter A 0 :
V is the volume of the chamber (27 m 3 );
L is the light path length (3 m); n is the number of units of test specimen
The extinction area of the smoke (S) can be calculated from A m or A 0 as follows:
Repeatability and reproducibility
Repeatability and reproducibility have been determined in an interlaboratory trial, based on IEC 61034-2
The results, presented in accordance with ISO 5725-2, are given in Annex C.
Relevance of test data and special observations
This method was initially created to assess smoke release from cables and other products used in underground railways The parameters of the fire scenario, including test chamber geometry, fire source, and specimen positioning, are specifically tailored to reflect conditions in underground railways It effectively simulates the conditions outlined in ISO 19706, fire stage 2.
The optical system employed is unable to differentiate between products that release smoke, leading to a light transmission through the chamber of less than 10% Consequently, the data provided is not directly applicable for quantitative fire hazard assessment or fire safety engineering; however, with additional processing, it may become suitable for such purposes.
In some countries, this method is used as the basis for regulatory control
This method can be further developed for various electrotechnical products, provided that the physical fire model is suitable and the constraints on test specimen geometry and discrimination are acceptable.
Determination of specific optical density using a dual-chamber test
Standards
One international technical report, ISO/TR 5924 [14], is based on the following method.
Purpose and principle
This test is used to assess the opacity of smoke generated by materials or products subjected to a specified thermal irradiance in a closed dual chamber.
Test specimen
The test specimen measures 165 mm × 165 mm and has a maximum thickness of 70 mm.
Method
Test specimens are horizontally mounted in a decomposition chamber and subjected to thermal irradiance levels reaching 60 kW/m² The smoke produced is captured in a secondary chamber, where its opacity is subsequently measured.
Repeatability and reproducibility
Relevance of test data and special observations
This method is now little used, has essentially been superseded by ISO 5659-2, and is now regarded as obsolescent
It is not recommended for further development
General
The dynamic test methods discussed here are chosen based on their status as published international, national, or industry standards widely used in the electrotechnical field This review does not aim to cover every possible test method.
NOTE These summaries are intended as a brief outline of the test methods and should not be used in place of full published standards.
Determination of smoke density generated by electric cables mounted on a
Standards
Several national and industry standards are based on the following method For example, NFPA 262 [15], ULC S102.4 [16], and EN 50289-4-11 [17].
Purpose and principle
This test is used to assess the smoke obscuration generated by cables in a horizontal tunnel with induced draught.
Test specimen
Test specimens consist of cables in 7,32 m lengths installed in a single layer over the rungs of a cable ladder 286 mm wide.
Method
The test specimens are subjected to a 300,000 BTU/h (87.9 kW) flame for 20 minutes within a tunnel, with a forced air flow directed away from the ignition source Throughout the test, the peak and average optical density of the smoke are recorded at the tunnel's opposite end using a photo cell.
Repeatability and reproducibility
An interlaboratory trial involving five laboratories has been carried out to evaluate NFPA 262 The results are given in Annex D.
Relevance of test data and special observations
This method is used to simulate a specific fire scenario involving movement of environmental air with severe fire source and ventilation conditions
The method is able to replicate ISO 19706, fire stage 3b (see Table 1)
This method is used to provide data for the regulatory control of some types of cables, in some countries.
Determination of smoke generated by electrical cables mounted on a vertical
Standards
There are two north American vertical ladder standards that involve the measurement of smoke These are ASTM D5424 [18] and UL 1685 [19]
Cables are installed on a vertical ladder within a chamber that maintains controlled air flow The measurement of smoke obscuration is conducted, alongside calculations for smoke release rate and total smoke release Additionally, mass loss and heat release may be assessed in certain instances.
Cables are mounted on a ladder in several configurations depending on the specified protocol
The ladder containing the cables is mounted vertically inside the enclosure, and optionally on a load cell
The cable(s) is(are) exposed to a 20 kW flame for 20 min The smoke obscuration is measured by a photoelectric cell located in the exhaust duct
A smoke release rate (SRR) is calculated using the extinction coefficient in the duct and the volumetric flow rate
7.3.1.5 Relevance of test data and special observations
These methods are adaptations of the standard cable industry tests for flame propagation, with instrumentation added to the exhaust duct to allow for the dynamic measurement of smoke
Test specimens are linear, should be self-supporting and should normally be installed vertically in enclosed ducts
The ventilation conditions and fire source are such that the test method is able to replicate ISO 19706, fire stage 2 (see Table 1)
This method is ideal for advancing electrotechnical products, provided that the installation environment is appropriate, the test specimen geometry meets acceptable limitations, and the physical fire model is suitable.
This method is used to provide data for the regulatory control of cables designated low smoke in the United States and Canada.
prEN 50399
There is a European vertical ladder standard that involves the measurement of smoke This is prEN 50399 [20]
7.3.2.2 Purpose and principle prEN 50399 specifies the test apparatus and test procedures for the assessment of the reaction to fire performance of cables It was developed from the FIPEC research programme
[21] in response to the European Construction Products Directive (CPD) [22] to enable classification under the CPD to be achieved
The test method involves a real-scale fire test of cable samples mounted on a vertical cable ladder, utilizing a specified ignition source to assess the burning behavior of the cables This test generates crucial data regarding the early stages of a cable fire, focusing on the ignition of cable samples It evaluates the risk of flame propagation along the cable, the potential impact on adjacent areas through heat release rate measurements, and the hazard of reduced visibility due to the production of light-obstructing smoke in the room of origin and surrounding enclosures.
During the test, several key parameters can be assessed under specific conditions, including flame spread, heat release rate, total heat release, smoke production rate, total smoke production, fire growth rate index, and the presence of flaming droplets or particles.
The apparatus is designed in accordance with EN 60332-3-10, featuring modifications to the mounting and airflow within the chamber, along with enhanced instrumentation for measuring heat release and smoke production during testing.
NOTE 1 The mounting changes make comparison with EN 50266-1 tests impossible.
NOTE 2 The IEC standard which corresponds to EN 50266-1 is IEC 60332-3-10 [24]. prEN 50399 contains two protocols In one protocol the flame ignition source has a nominal power of 20,5 kW In the other protocol it has a nominal power of 30 kW
There are three different classifications for smoke based on this test They are based on the total smoke production and the peak rate of smoke production
The test specimens consist of cables measuring (3.5 +0.1 – 0.0) meters in length The loading and spacing of these specimens on the ladder are determined by the diameter of the cable.
Cables are positioned at the front of a vertical ladder within the test enclosure The heat release rate is calculated by assessing the oxygen concentration, flow rate, and temperature in the exhaust duct, based on the principle of oxygen consumption.
The airflow through the test chamber is 8,0 m 3 × min -1 ± 0,8 m 3 × min -1
The test flame is applied for 20 min, after which it is extinguished The air flow through the test chamber is maintained for a further 30 s after which it is stopped
CLC/TC20/Sec1576/INF [26] is a report of round-robin tests carried out in support of the development and finalistion of prEN 50399 The round-robin especially evaluated repeatability and reproducibility
The test, created in Europe to comply with the European Construction Products Directive, is essential for four classes specified by the European Commission This test data enables EU member states to implement a unified system for classifying the fire performance of cables utilized in buildings for the first time.
Research has shown that additional measurement techniques, validated for standard tests on building products, are effective for evaluating the fire performance of electric cables These methods encompass measurements of heat release and smoke production.
The test does not have the resolution to be able to differentiate products that produce very low levels of smoke Such products are currently assessed using the 3 m cube – see 6.3.
Determination of smoke using a cone calorimeter
Standards
Two standards, one national and one international, are based on the following method These are ASTM E1354 [27] and ISO 5660-2 [28].
Purpose and principle
This test evaluates the smoke obscuration from specimens subjected to a truncated cone heater in high ventilation conditions The generated smoke is channeled through a duct, where both the extinction coefficient and volumetric flow rate are measured.
Test specimen
The test specimen is a flat piece, 100 mm × 100 mm, with a maximum thickness of 50 mm.
Method
The test specimen is exposed to a heat flux of up to 100 kW/m 2 from a conical heater and the combustion gases are ignited using a spark ignitor
The cone calorimeter is an effective testing method that simultaneously evaluates multiple parameters, including smoke production It utilizes horizontally oriented test specimens, with smoke being drawn from the combustion area into a duct at a rate of 24 dm³/s This smoke is monitored using a helium neon laser and a twin silicon photodiode system The results are reported as the specific extinction area (\$σ_f\$), which is calculated from the extinction coefficient, volume flow rate, and mass loss rate.
V • is the volume flow rate; m • is the mass loss rate; k is the extinction coefficient [= (1/L) ln(I /T)]
NOTE It is important to realise that σ f does not give information on the rate of smoke production in a fire
The rate of smoke production is given by:
The average specific extinction area of smoke (σ f avg ) is then calculated as follows: m S m t k avg V f ∆ = ∆
∆t is the time interval between data readings;
The total extinction area of smoke is given by:
S=∑ • ∆ The total extinction area of smoke produced is also given by:
S d and can be found by calculating the area under the S • versus the time graph.
Repeatability and reproducibility
An interlaboratory trial involving seven laboratories was carried out during the development of ISO 5660-2 The results, presented in accordance with ISO 5725, are given in Annex E.
Relevance of test data and special observations
The cone calorimeter, initially designed to assess heat release through oxygen consumption, is frequently enhanced with a laser system for real-time smoke measurement.
The cone calorimeter is commonly utilized for fire modeling and hazard assessment, yet it has notable limitations that hinder its application for electrotechnical products Firstly, the test specimen must be small and essentially flat Secondly, the unrestricted air access to the specimen confines the method to replicating only specific fire stages as outlined in ISO 19706, specifically stages 1b) and 2.
This method could provide the basis for further development as a method for electrotechnical products, provided that the test specimen geometry is essentially flat, and representative of end product use
Data from this test should not be used in isolation as the basis for regulatory control of smoke release from electrotechnical products
8 Overview of methods and relevance of data
The methods described in Clauses 6 and 7 are summarized in Table 2, highlighting the limitations of the test method and its applicability to the fire stages outlined in Table 1 Product committees looking to adopt or modify these test methods must verify that the chosen method is appropriate and suitable for its intended use.
Dynamic test methods generally provide test data in a format suitable for input to fire hazard assessment, or fire safety engineering
The methods discussed rely on diverse physical fire models and varying test specimen geometries, significantly influencing the smoke obscuration produced by materials or products Consequently, it is important to note that the ranking of smoke obscuration data from one test cannot be assumed to align with the ranking from another test.
In addition, there are many ways of expressing smoke obscuration data which means that the data from different methods cannot be directly compared, without further calculation
Table 2 provides an overview of smoke test methods, detailing the type of test method, clause references, limitations on test specimens, relevance to the stage of fire, and suitability of data format for input to fire safety engineering The static method 6.2.1 focuses on determining smoke opacity in a 0.51 m³ chamber using a vertically oriented test specimen.
The material is essentially flat, measuring less than 76.2 mm × 76.2 mm, and is not suitable for liquids or certain thermoplastics It is not recommended for use in applications requiring smoke opacity determination in a 0.51 m³ chamber with a horizontally oriented test specimen.
E ss ent ial ly fl at onl y, and les s than 75 m m × 75 m m P os si bl y sui tabl e for pr oduc ts ( see 6 2)
No Y es No Y es Y es No
Only use products with the appropriate geometry and for the relevant first stage The determination of smoke opacity should be conducted in a 27 m³ smoke chamber, as currently reported.
Materials or products, typically cables, should be approximately 1 meter long and are only to be used for the relevant first stage The determination of specific optical density is conducted using a dual-chamber test.
165 m m × 165 m m , m ax im um thi ck nes s of 70 m m No Y es No Y es No No N ow r egar ded as obs ol es cent N ot as c ur rent ly r epor ted
Table 2 outlines various test methods and their corresponding limitations regarding test specimens, relevance to fire stages, regulatory use, and data suitability for fire safety engineering Specifically, it includes the dynamic determination of smoke opacity generated by electric cables mounted on a horizontal ladder.
E ss ent ial ly fl at bui ldi ng pr oduc ts or c abl es No No No No No Y es
S houl d onl y be us ed for pr oduc ts w ith the appr opr iat e geom et ry and for the rel ev ant fi re st age
The determination of smoke opacity generated by electrical cables mounted on a vertical ladder is outlined in ASTM D 5424 and UL 1685 standards.
Electrical or optical wires and cables should only be used for their intended purpose and relevant fire stages The determination of smoke opacity generated by electrical cables mounted on a vertical ladder is outlined in standard prEN 50399.
Electrical or optical wires and cables should only be used for their intended purposes and relevant fire stages The determination of smoke opacity can be conducted using a conical orimeter.
Int ended for es sent ial ly flat m at er ial s P os si bl y sui tabl e for pr oduc ts ( see 7 3)
No Y es No Y es No Y es
Only use data for products that have the appropriate geometry and are relevant to the specific fire stage The suitability of data for fire safety engineering is limited to applications where the testing method corresponds to the relevant fire stage.
NBS smoke chamber – Interlaboratory tests from the French standard
The evaluation of four materials utilized in electrotechnical products, including three types used in electric cables, was conducted using 14 NBS smoke chambers, following the procedures outlined in the French standards NF C20-902-1 and NF C20-902-2.
The results of these tests related to the determination of D m are summarised in the following table
21 m is the average specific optical density (D m ); r is the repeatability;
S r is the standard deviation of repeatability;
S R is the standard deviation of reproducibility
Repeatability and reproducibility data – ISO 5659-2
Reproducibility (between laboratories) r % of mean R % of mean
72 a + pf indicates a test carried out in mode 2 (i.e with pilot flame)
Table B.2 – Test results for poly-carbonate
NOTE The distance between the test specimen and the heater was 50 mm
* Most of the laboratories reported that the D s10 and D s max exceeded 500
Table B.3 – Test results for PVC flooring
NOTE The distance between the test specimen and the heater was 50 mm
"Three metre cube" smoke chamber – French interlaboratory tests according to IEC 61034-2
Three types of cables were evaluated by seven laboratories using the "three metre cube" chamber in accordance with the procedure described in the first edition of IEC 61034-2 (1991)
The results of these tests, related to the determination of the percentage transmission of light through the smoke, are summarized in Table C.1
Table C.1 – Measurement of transmission expressed as a percentage
Cable type studied Flexible cable
4 m is the average percentage transmission value; r is the repeatability;
S r is the standard deviation of repeatability;
S R is the standard deviation of reproducibility
NOTE This interlaboratory test was carried out using the first edition of IEC 61034-2 Some technical improvements are described in the second and third editions
Repeatability and reproducibility data – NFPA 262
Five laboratories were involved in this international interlaboratory test [29]
The smoke measurement system is calibrated using neutral density filters ranging from 0.1 to 1.0, ensuring that the measured optical density exhibits a linear response with a regression coefficient of at least 0.99 The results for optical density are reported with a precision of 0.01.
The method used to determine the repeatability and reproducibility was ISO 5725
The average value (m), repeatability (r), and reproducibility (R), were calculated for each of six cable test specimens
Precision data of smoke measurement in ISO 5660-2