Material combustion product toxicity testing quantifies the toxic gases—such as carbon monoxide, hydrogen cyanide, and hydrogen halides—released when polymers, cables, composites, and interior materials decompose or burn. By applying internationally recognized methods from ISO, IEC, ASTM, EN, and GB standards, accredited third-party laboratories determine gas yields, lethal toxic potency (LC50), fractional effective dose (FED), and toxicity indices that support product certification, material selection, and fire safety engineering. This article explains the sample types, test items, analytical methods, and typical applications of combustion toxicity testing.
Technical Overview
Smoke inhalation, rather than direct flame contact or burns, is the dominant cause of incapacitation and death in building fires, accounting for the majority of fire fatalities in most reported incident statistics. When organic materials undergo thermal decomposition or combustion, the resulting fire effluents contain a complex mixture of asphyxiant gases, irritant gases, and organic volatiles whose composition depends on the material chemistry, temperature, oxygen availability, and whether decomposition occurs in flaming or non-flaming mode. Material combustion product toxicity testing is therefore designed to generate effluents under controlled and reproducible conditions, chemically characterize the gases produced, and convert the analytical results into hazard metrics that regulators and fire safety engineers can use.
The principal toxic species of concern fall into functional groups. Asphyxiant gases include carbon monoxide (CO), which arises from incomplete oxidation of carbonaceous fuels, and hydrogen cyanide (HCN), which is generated by nitrogen-containing polymers such as polyurethanes, polyamides, ABS, melamine resins, and acrylic fibers. Irritant gases include the hydrogen halides HCl, HBr, and HF produced by halogenated polymers such as PVC and fluoropolymers as well as halogenated flame retardants, together with sulfur dioxide, nitrogen oxides, ammonia, formaldehyde, acrolein, and isocyanates. Carbon dioxide acts indirectly by stimulating respiration and accelerating the uptake of CO and HCN. Standards bodies including ISO, IEC, ASTM, EN, GB, and IMO have established test frameworks in which these gases are measured and reduced to indices such as the fractional effective dose (FED), lethal toxic potency (LC50), conventional index of toxicity (CIT), or a graded hazard classification.
Regulatory demand for such data is strong in sectors where occupants cannot easily escape from fire: railway and metro vehicles governed by EN 45545-2, ships and offshore installations governed by the IMO FTP Code, public assembly buildings in China governed by GB 8624 and GB 20286 with grading based on GB/T 20285, and low-smoke halogen-free cable systems governed by IEC 60754 and EN 50267. Accredited third-party laboratories perform these tests to support certification, product development, and fire hazard analysis.
Testing Samples
Polymeric Materials and Compounds
Thermoplastics such as PE, PP, PS, ABS, PC, PA, and POM, thermosets such as epoxy, phenolic, and unsaturated polyester resins, polyurethane and silicone foams, and elastomers are tested as pellets, plaques, films, or machined specimens. Compounders and formulators use the results to compare resin grades, flame-retardant packages, filler loadings, and stabilizer systems.
Wires, Cables, and Cable Materials
Insulation compounds, sheathing compounds, bedding materials, and finished cables are evaluated for halogen acid gas evolution, acidity, and combustion gas toxicity. These data substantiate low-smoke zero-halogen (LSZH) declarations and support classification of cable systems for rail, marine, building, and infrastructure projects.
Railway and Metro Interior Materials
Seat cushions and covers, headrests, wall and ceiling linings, GRP panels, floor coverings, driver cab components, ducting, adhesives, and coating systems are tested against the requirement sets of EN 45545-2 at the appropriate hazard level (HL1 to HL3), including the smoke chamber gas analysis used to derive the conventional index of toxicity.
Marine and Offshore Materials
Surface materials, bulkhead and ceiling linings, floor coverings, and primers and paints used on ships, ferries, and offshore platforms are tested under the IMO 2010 FTP Code, Part 2, which combines smoke production measurement with concentration limits for designated toxic gases.
Building Products and Public Place Materials
Decorative finishes, wall coverings, thermal insulation, upholstered furniture components, and flame-retarded products intended for public assembly occupancies are assessed using GB/T 20285 smoke toxicity grading referenced by GB 20286, alongside other reaction-to-fire properties required by GB 8624.
Electrical, Electronic, and Battery Materials
Equipment enclosures, connectors, PCB laminates, potting compounds, battery module housings, separators, and electrolyte-related decomposition studies increasingly require gas toxicity characterization, particularly for energy storage systems and electric vehicles where fluorinated chemistry can yield HF under abuse conditions.
Textiles, Foams, and Furnishings
Upholstery fabrics, curtains, mattresses, and flexible foams are tested because of their large exposed surface area and their tendency to smolder, generating high CO yields during non-flaming decomposition.
Testing Items
Testing programs typically combine gas speciation with derived hazard metrics. The most commonly reported items include the following:
- Asphyxiant gases: carbon monoxide (CO), carbon dioxide (CO2), hydrogen cyanide (HCN), and oxygen depletion
- Irritant and acid gases: hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen fluoride (HF), sulfur dioxide (SO2), nitric oxide (NO), nitrogen dioxide (NO2), and ammonia (NH3)
- Organic species: formaldehyde, acrolein, benzene, toluene, styrene, phenol, and isocyanates
- Concentrations (ppm or mg/m3) and mass yields (mg of gas per g of specimen consumed)
- Fractional effective dose (FED) and fractional effective concentration (FEC) calculated according to ISO 13571
- Lethal toxic potency (LC50) estimated according to ISO 13344 or measured per ASTM E1678
- Conventional index of toxicity (CIT) required by EN 45545-2 for railway applications
- Combined toxicity index per defense-oriented specifications such as NES 713
- Smoke toxicity hazard grade per GB/T 20285, including the quasi-safe AQ sub-levels used in Chinese public place regulations
- Halogen acid gas content and aqueous acidity (pH and conductivity) per IEC 60754-1, IEC 60754-2, and EN 50267-2 for cables
Testing Methods
Static Decomposition and Combustion Chamber Methods
Static methods expose a small specimen to a controlled thermal environment inside a closed system, allow the effluent to equilibrate, and then sample the well-mixed atmosphere. GB/T 20285 uses a quartz tube furnace operating at defined temperatures to pyrolyze or combust the specimen, with gases collected and analyzed to compute lethal-threshold-based hazard grades. NES 713 burns the specimen in a sealed chamber and calculates a combined toxicity index by summing the measured concentrations of a defined set of gases normalized against their hazardous reference concentrations. Static methods are reproducible and inexpensive, making them suitable for screening and regulatory grading, although the fixed ventilation condition does not replicate developing fires.
Dynamic Flow Tube Furnace Methods
Dynamic methods move a primary air stream through a heated tube in which the specimen decomposes, so that gas concentrations reach a steady state and can be related directly to decomposition conditions. The ISO 19700 steady-state tube furnace supports well-ventilated and vitiated (under-ventilated) combustion scenarios across a range of furnace temperatures and fluxes, producing yield data that feed directly into ISO 13344 LC50 calculations and ISO 13571 tenability assessments. The related IEC/TS 60695-7-50 and 60695-7-51 procedures address toxic potency within the electrotechnical fire testing framework, NF X 70-100 provides a tube furnace approach widely used for French railway and aerospace materials, and ASTM E1678 determines the lethal toxic potency of smoke using a dynamic crucible furnace configuration.
Smoke Chamber Method with Effluent Gas Analysis
The ISO 5659-2 smoke chamber, an NBS-type chamber of approximately 0.5 m3 volume, exposes 75 mm by 75 mm horizontal specimens to radiant fluxes of 25 kW/m2 or 50 kW/m2, with or without piloted ignition. When coupled with continuous gas sampling and FTIR analysis, the same test yields both smoke density parameters, such as Ds(max) and VOF4, and time-resolved toxic gas concentrations. EN 45545-2 uses this configuration to calculate CIT values for railway requirement sets, while the IMO 2010 FTP Code Part 2 applies the chamber with gas concentration limits for CO, HCl, HBr, HF, SO2, NOx, and HCN for shipboard surface materials.
Cable-Specific Chemical Methods
For cable materials, IEC 60754-1 and EN 50267-2-1 determine the amount of halogen acid gas evolved during combustion, while IEC 60754-2 and EN 50267-2-2 absorb the combustion gases in water and measure pH and conductivity to characterize acidity and corrosivity. Typical acceptance criteria for halogen-free declarations include pH not lower than 4.3 and conductivity not exceeding 10 µS/mm, subject to the prevailing specification.
Gas Analysis Instrumentation
Fourier transform infrared spectroscopy operated according to ISO 19702 provides simultaneous, continuous quantification of most fire gases, including HCN and the hydrogen halides, and is the preferred technique for smoke chamber and tube furnace coupling. Supplementary techniques include non-dispersive infrared analyzers for CO and CO2, paramagnetic or electrochemical sensors for oxygen, chemiluminescence analyzers for NOx, ion chromatography of absorbed solutions for fluoride and halide species, gas detection tubes for screening-level methods such as GB/T 20285 and NF X 70-100, and gas bags followed by gas chromatography-mass spectrometry for volatile organic species. General guidance on sampling and analysis of fire atmospheres is given in ISO 19701, ASTM E800, and the IEC 60695-7 series.
Calculation of Hazard Metrics
Raw concentrations are converted into decision-ready metrics using standardized dose-effect models. FED accumulates the ratio of exposure to the incapacitating dose of asphyxiants, incorporating the synergistic effect of CO2 on uptake of CO and HCN, while FEC accumulates irritant effects on escape capability, both per ISO 13571. LC50 values express the smoke concentration lethal to 50 percent of an exposed population, estimated from FED calculations per ISO 13344 or determined experimentally per ASTM E1678. CIT ratios the measured gas concentrations against reference values defined in EN 45545-2 and scales the result to classify materials across hazard levels HL1, HL2, and HL3.
Applications
Combustion toxicity testing data are used across the product life cycle and across industries:
- Certification of railway and metro interior materials against EN 45545-2 requirement sets for hazard levels HL1 through HL3
- Type approval of shipboard surface materials under the IMO FTP Code and SOLAS-related acceptance procedures
- Compliance demonstration for flame-retarded products used in public assembly occupancies under GB 20286 and GB 8624
- Verification of low-smoke zero-halogen cable claims and support for project specifications in rail, tunnel, and building installations
- Research and development screening of polymer formulations, flame retardants, fillers, and intumescent systems to minimize toxic gas yields
- Fire safety engineering studies that feed measured gas yields into tenability analysis, evacuation modeling, and performance-based design documentation
- Quality control of incoming resins and compounds and batch release testing for critical transportation programs
- Post-incident investigation and litigation support, where effluent chemistry helps reconstruct exposure conditions
- Emerging applications in lithium-ion battery energy storage, electric vehicle interiors, and aircraft cabin materials where specialized specifications add toxic gas analysis to smoke testing
FAQ
Why is toxicity testing performed separately from flammability testing?
Flammability tests measure ignition, flame spread, and heat release, but they do not characterize the chemical hazard of the smoke. Two materials with identical flame spread ratings can produce very different effluent toxicities, for example when a nitrogen-containing polymer yields HCN or a halogenated polymer yields HCl. Dedicated toxicity testing is therefore required wherever standards or specifications impose limits on combustion gases.
How do I select the appropriate test method?
Selection follows the end-use regulation. Use EN 45545-2 smoke chamber gas analysis with CIT calculation for railway materials, IMO FTP Code Part 2 for marine surfaces, GB/T 20285 grading for Chinese public place products, IEC 60754 series for cable compounds, and ISO 19700 or ASTM E1678 tube furnace methods when LC50 and yield data are needed for research or fire engineering. Accredited third-party laboratories can advise on the requirement set that matches your product category and application.
What sample form and quantity are required?
Requirements depend on the method: ISO 5659-2 requires 75 mm by 75 mm plaques at product thickness, typically several specimens per condition; tube furnace methods use small quantities of granulated or cut material across a range of furnace conditions; and IEC 60754 uses approximately 1 g of compound per determination. Specimens are normally conditioned at 23 °C and 50 percent relative humidity before testing.
Are halogen-free materials automatically low in toxicity?
No. Removing chlorine and bromine eliminates HCl and HBr, but halogen-free materials can still produce high yields of CO under vitiated combustion, and nitrogen-containing formulations can generate lethal concentrations of HCN. Full-spectrum gas analysis, rather than halogen content alone, is needed to characterize toxicity.
What do FED, FEC, LC50, and CIT mean in practical terms?
FED expresses cumulative exposure to asphyxiant gases as a fraction of the dose that would incapacitate an exposed person, FEC expresses irritant effects that impair escape, LC50 expresses the smoke concentration lethal to half of an exposed population, and CIT is a dimensionless benchmark index used to rank railway materials against reference gas concentrations. A FED reaching 1.0, an LC50 achieved at low mass loss, or a CIT above the specification limit each indicate elevated toxic hazard.
How long does testing take?
Single-condition screening tests such as IEC 60754 acidity measurements are typically completed within one to two weeks, while multi-condition programs such as full EN 45545-2 qualification involving toxicity, smoke density, and flammability components, or multi-temperature ISO 19700 campaigns, may require several weeks because of specimen preparation, conditioning, calibration, and replicate determinations.
Do current methods avoid animal exposure testing?
Modern standards are predominantly instrumental. Lethal potency is estimated analytically from gas concentrations using the FED methodology of ISO 13344 and ISO 13571, and older animal-based procedures such as the original ASTM E1678 protocol have largely been replaced by gas analysis with mathematical dose-effect models.