Plastic Combustion Decomposition Gas Testing: Standards, Methods, and Safety Assessment

Plastic combustion decomposition gas testing evaluates the toxic, corrosive, and flammable gases released when polymeric materials burn or thermally decompose, providing critical fire safety data for material selection, product development, and regulatory compliance. This guide explains the key test items, internationally recognized methods such as IEC 60754 and ISO 19700, typical sample types, and industry applications ranging from railway vehicles to wire and cable manufacturing.

Technical Overview

Plastics are organic polymers that undergo pyrolysis and thermal decomposition when exposed to elevated temperatures, typically between 200 °C and 600 °C depending on the polymer chemistry. During this process, polymer chains break down into smaller molecular fragments, releasing a complex mixture of gases, condensable liquids, and solid residues. When these decomposition products ignite, secondary combustion reactions generate additional gaseous species whose composition depends on the material formulation, oxygen availability, and fire temperature.

Fire safety statistics consistently show that the majority of fire fatalities result from inhalation of toxic smoke rather than direct flame exposure. For this reason, combustion gas analysis is a core element of material hazard assessment. The gases evolved from burning plastics are generally classified into three categories:

• Asphyxiant gases: carbon monoxide (CO), carbon dioxide (CO2), and hydrogen cyanide (HCN), which reduce oxygen delivery and cause incapacitation
• Irritant and corrosive gases: hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen fluoride (HF), sulfur dioxide (SO2), nitrogen oxides (NOx), aldehydes, and acrolein, which attack the respiratory tract and damage electronic equipment
• Flammable gases and unburned hydrocarbons: methane, ethylene, styrene monomer, benzene, and other volatile organic compounds that can sustain or propagate fire

Modern combustion gas testing simulates different fire stages—smoldering, developing fire, and fully developed fire—under controlled furnace conditions. Results are typically expressed as gas yield (mg of gas per g of material), gas concentration (ppm), acidity (pH and conductivity of the absorbed gas solution), toxicity index, or fractional effective dose (FED) values used in fire hazard engineering calculations.

Testing Samples

Wire and Cable Materials

Insulation and sheathing compounds are among the most frequently tested plastic products due to their widespread installation in confined spaces. Typical samples include PVC-based compounds, cross-linked polyethylene (XLPE), ethylene-vinyl acetate (EVA), and halogen-free flame retardant (HFFR or LSZH) compounds used in power, control, and communication cables.

Engineering Thermoplastics

Structural and functional polymers such as polyamide (PA), polycarbonate (PC), acrylonitrile butadiene styrene (ABS), polybutylene terephthalate (PBT), polyoxymethylene (POM), polymethyl methacrylate (PMMA), polyurethane (PU), and fluoropolymers such as PTFE are tested to characterize their specific decomposition products, including HCN from nitrogen-containing polymers and HF from fluoropolymers.

Foam, Elastomeric, and Composite Materials

Flexible and rigid polyurethane foams, silicone elastomers, phenolic resins, glass-fiber reinforced plastics, and composite panels used in seating, insulation, and paneling are evaluated because of their large exposed surface area and high fuel load in fire scenarios.

Finished Components and Assemblies

Cut specimens from finished products—electronic equipment enclosures, vehicle interior panels, aircraft cabin parts, floor coverings, and pipe insulation—may be tested directly to assess the actual material as supplied, including additives, fillers, and flame retardants.

Acceptable sample forms include granules, pellets, plaques, compression-molded sheets, and small pieces cut from finished articles. Depending on the specific method, the required specimen mass typically ranges from approximately 0.5 g to 20 g per test condition.

Testing Items

Depending on the applicable standard and the intended application, plastic combustion decomposition gas testing may cover the following analytical items:

• Asphyxiant gases: carbon monoxide (CO), carbon dioxide (CO2), hydrogen cyanide (HCN)
• Hydrogen halides: hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen fluoride (HF)
• Sulfur and nitrogen compounds: sulfur dioxide (SO2), nitrogen monoxide (NO), nitrogen dioxide (NO2), ammonia (NH3), hydrogen sulfide (H2S)
• Low-molecular-weight irritants: formaldehyde, acetaldehyde, acrolein
• Aromatic and volatile organic species: benzene, toluene, ethylbenzene, styrene, phenol
• Flammable gases: methane, ethane, ethylene, propylene
• Halogen acid gas content expressed in mg/g of sample (IEC 60754-1)
• Acidity of evolved gases: pH value and conductivity of the absorption solution (IEC 60754-2)
• Smoke production: specific optical density and smoke density rating
• Toxicity evaluation: toxicity index, FED (asphyxiants) and FEC (irritants) calculations

Testing Methods

Halogen Acid Gas Evolution (IEC 60754 / EN 50267 / GB/T 17650)

A weighed specimen is heated in a combustion tube under a controlled airflow at a specified furnace temperature, and the evolved gases are captured in an absorption solution. In IEC 60754-1, the absorbed halogen acid content is determined by analytical chemistry and expressed in mg/g, with a common pass criterion of less than 5 mg/g for halogen-free declarations. IEC 60754-2 determines the pH and conductivity of the gas absorption solution, with typical acceptance values of pH ≥ 4.3 and conductivity ≤ 10 μS/mm for low-acidity materials. The EN 50267 series and GB/T 17650 series describe equivalent procedures widely specified for cable materials.

Steady-State Tube Furnace (ISO/TS 19700)

The ISO/TS 19700 method places the sample in a quartz tube furnace with a controlled secondary air feed, allowing the combustion condition (flammation, smoldering, or pyrolysis) to be established and maintained at a steady state. This enables measurement of gas yields under well-defined equivalence ratios, providing input data for fire hazard engineering and FED-based toxicity assessment.

Tubular Furnace Method (NF X 70-100)

This French tube furnace method decomposes small test pieces in a stream of air at fixed temperatures, commonly 600 °C and 800 °C, with subsequent gas analysis for CO, CO2, HCN, HCl, HBr, HF, SO2, NOx, and organic species. It is the reference procedure underlying the smoke toxicity requirements of EN 45545-2 for railway applications.

Smoke Density Chamber (ISO 5659-2 / ASTM E662)

Specimens are exposed to a radiant heat source (with or without pilot flame) inside a closed chamber, and light transmission across the chamber path is recorded to calculate specific optical density. Modern instrumentation combines the chamber with Fourier-transform infrared (FTIR) gas analyzers to measure the concentrations of principal toxic gases simultaneously with smoke production.

Cone Calorimeter and FTIR Coupling (ISO 5660-1)

The cone calorimeter measures heat release rate, ignition time, and mass loss under controlled irradiance levels. When coupled to FTIR gas analysis, it also yields real-time concentration profiles of CO, CO2, HCN, HCl, and other species, supporting comprehensive fire hazard characterization.

Analytical Techniques

Gas quantification is performed using ion chromatography for hydrogen halides, FTIR spectroscopy for multi-component real-time analysis, gas chromatography for hydrocarbon speciation, electrochemical sensors for CO and NOx, and colorimetric detection tubes for rapid screening of specific species such as HCN.

Applications

Combustion decomposition gas testing is applied across industries where fire performance and occupant safety are regulated:

• Railway vehicles: demonstration of compliance with EN 45545-2 smoke and toxicity requirements for interior materials, seating, and cables
• Shipbuilding and marine engineering: qualification of materials under the IMO FTP Code, including smoke generation and toxicity criteria for accommodation and machinery spaces
• Wire and cable manufacturing: verification of low smoke zero halogen (LSZH) properties per IEC 60754 series for installations in tunnels, data centers, and public buildings
• Construction products: supporting fire classification under EN 13501-6 and related national building codes
• Automotive and aerospace: evaluation of cabin interior materials, thermal-acoustic insulation, and cable harnesses
• Electronics and electrical equipment: hazard analysis of enclosures, connectors, and printed circuit board substrates under abnormal thermal events
• Research and development: formulation optimization of flame retardant systems, halogen substitution studies, and comparative material benchmarking

Accredited third-party laboratories providing these services can issue test reports accepted for regulatory submissions, tender documentation, and certification programs worldwide.

FAQ

What is the difference between flame retardance testing and combustion gas testing?

Flame retardance tests (such as UL 94 or the limiting oxygen index) evaluate whether a material ignites and how flames propagate, while combustion gas testing characterizes the chemical composition and toxicity of the gases released when the material decomposes. A self-extinguishing material can still evolve highly toxic gases, so both aspects must be assessed for a complete fire hazard profile.

How much sample is required for testing?

Typical requirements are approximately 1 g per test condition for IEC 60754, around 20 g in total for NF X 70-100 testing at multiple temperatures, and specimens of 75 mm × 75 mm for ISO 5659-2 smoke chamber testing. Accredited laboratories confirm exact quantities based on the selected standards.

What do "low halogen" and "halogen-free" mean in practice?

Under IEC 60754-1, materials with evolved halogen acid content below 5 mg/g are commonly regarded as halogen-free, while IEC 60754-2 acidity limits (pH ≥ 4.3, conductivity ≤ 10 μS/mm) address corrosive gas emission. Specific procurement specifications may impose stricter limits, so the agreed contractual criteria should always be checked.

What are FED and FEC?

The Fractional Effective Dose (FED) model estimates the combined incapacitating effect of asphyxiant gases (CO, CO2, HCN) on occupants, while the Fractional Effective Concentration (FEC) model addresses sensory irritation from gases such as HCl and acrolein. Both are used in fire safety engineering, notably within EN 45545-2.

How long does combustion gas testing take?

Single-method tests such as IEC 60754 typically require five to ten working days including report issuance, while multi-temperature toxicity programs covering several gas species may take two to four weeks. Exact lead times depend on the number of test conditions and the complexity of the analytical package.