Plastic Combustion Corrosive Gas Analysis: Standards, Methods, and Applications

Plastic combustion corrosive gas analysis quantifies the acidic gases—primarily HCl, HBr, HF, and SO2—that polymeric materials release when they burn, using standardized procedures such as IEC 60754-1 and IEC 60754-2. This testing is essential for qualifying low-smoke zero-halogen (LSZH) cable compounds, protecting sensitive electronics from secondary smoke damage, and demonstrating compliance with fire-safety specifications in rail, marine, data-center, and building applications. This article explains the technical principles, sample types, test items, methodologies, and typical applications of corrosive gas analysis for plastics.

Technical Overview

When plastics and other polymeric materials burn or thermally decompose, they evolve a complex mixture of gases. Depending on the formulation, these gases can include strongly corrosive and acidic species such as hydrogen chloride (HCl), hydrogen bromide (HBr), hydrogen fluoride (HF), sulfur dioxide (SO2), nitrogen oxides (NOx), and phosphorus-containing acids. Halogenated polymers such as PVC and halogenated flame retardants are the principal sources of hydrogen halides, while sulfur-cured rubbers and certain additives release sulfur oxides.

Corrosive combustion gases cause extensive secondary damage well beyond the immediate fire zone. Transported by smoke, they condense on cool surfaces and, in combination with firefighting water or ambient humidity, form aggressive acids that attack copper circuitry, silver contacts, protective coatings, steel structures, and concrete. Equipment never touched by flames is frequently written off after a fire solely because of acid deposition. For this reason, corrosivity performance is now specified in nearly every high-consequence sector, including rail transit, shipping, tunnels, data centers, and nuclear facilities.

Corrosive gas analysis subjects a representative plastic specimen to controlled combustion in a tube furnace, captures the evolved gases in absorption solutions, and quantifies them by titration, ion chromatography, or electrochemical measurement. The main international frameworks governing this testing are listed below.

• IEC 60754-1 / EN 50267-2-1 — Determination of the halogen acid gas content evolved during combustion of materials taken from cables
• IEC 60754-2 / EN 50267-2-2 — Determination of acidity (by pH measurement) and conductivity
• GB/T 17650.1 and GB/T 17650.2 — Chinese national standards technically equivalent to the IEC 60754 series
• EN 14582 — Determination of halogen and sulfur content by combustion in oxygen, followed by ion chromatography
• IEC 62321-3-2 — Determination of halogen content in electrotechnical products by combustion ion chromatography (CIC)
• ASTM D5485 — Determination of the corrosive effect of combustion products using the cone corrosimeter
• ISO 11907 series — Plastics: determination of the corrosivity of combustion products

Testing Samples

Corrosive gas analysis can be applied to virtually any organic polymeric material. Accredited third-party laboratories typically receive the following categories of samples for combustion corrosivity qualification.

Cable Insulation and Sheathing Compounds

Wire and cable materials dominate this testing field. Specimens include PVC insulation and sheaths, cross-linked polyethylene (XLPE), polyolefin-based low-smoke zero-halogen (LSZH/LSOH) compounds, ethylene-vinyl acetate (EVA) formulations, and mineral-filled flame-retarded sheathing compounds intended for rail, shipboard, and building cables.

Flame-Retardant Polymer Compounds

Materials containing halogenated flame retardants, such as brominated epoxy systems, brominated polystyrene, or chlorinated paraffins, are analyzed to determine how much HBr or HCl they release. The data support both compliance verification and reformulation programs directed toward halogen-free grades.

Engineering Plastics and Electronic Materials

Polycarbonate, ABS, polyamide (PA), PBT, thermoset moldings, connector housings, and printed circuit board laminates are tested under halogen-free initiatives. IEC 61249-2-21 defines halogen-free laminate criteria (chlorine ≤ 900 ppm, bromine ≤ 900 ppm, total chlorine plus bromine ≤ 1500 ppm), typically verified by combustion ion chromatography.

Rubbers, Elastomers, and Foams

Chloroprene rubber, fluoroelastomers, EPDM, silicone compounds, and flexible polyurethane foams are evaluated because halogen-containing elastomers and sulfur-based curing systems can contribute significant corrosive gas loads in confined spaces such as ships and rail vehicles.

Interior and Building Materials

Wall linings, floor coverings, seat fabrics, decorative laminates, adhesives, and cable trunking used in passenger cabins and public buildings are screened to demonstrate compliance with reaction-to-fire specifications such as EN 45545-2 for railway applications.

Testing Items

Depending on the specification invoked, one or more of the following parameters are determined and reported for each material.

• Hydrogen chloride and hydrogen bromide (HCl + HBr) evolved gas content, expressed as a mass percentage of the specimen
• Hydrogen fluoride (HF) content or total fluorine evolution for fluoropolymer-containing materials

pH value of the aqueous absorption solution of the combustion gases

• Conductivity of the absorption solution, typically reported in µS/mm
• Total halogen content (F, Cl, Br, I) and total sulfur content in mg/g by combustion ion chromatography
• Smoke corrosivity index, expressed as metal loss on copper targets or NaCl-equivalent deposition
• Compliance assessment against LSZH, FR-LS, halogen-free, or project-specific purchasing specifications

Testing Methods

Halogen Acid Gas Evolution — IEC 60754-1 / EN 50267-2-1

A pre-weighed specimen, commonly 500 mg to 1 g of granulated material, is pyrolyzed and combusted in a quartz tube furnace, typically at 800 °C, under a controlled stream of air. The evolved gases are swept through absorption vessels where the hydrogen halides are trapped in aqueous solution. The absorbed chloride and bromide are quantified by argentometric titration or, increasingly, by ion chromatography, and the combined HCl + HBr content is calculated as a mass percentage of the original specimen. Materials with a halogen acid gas content not exceeding 0.5% (5 mg/g) are conventionally regarded as halogen-free or low-halogen for cable qualification purposes.

Acidity and Conductivity — IEC 60754-2 / EN 50267-2-2

The specimen is combusted in the tube furnace, in this method typically at 935 °C, and the combustion products are absorbed in a defined volume of deionized water. The pH and the conductivity of the resulting solution are then measured at a controlled temperature. Standard acceptance criteria for low-halogen, low-corrosivity materials are pH ≥ 4.3 and conductivity ≤ 10 µS/mm. Because this method captures the aggregate contribution of all acidic species, including sulfur and phosphorus compounds, it is a broader indicator of combustion corrosivity than the halogen-specific Part 1 procedure.

Combustion Ion Chromatography — EN 14582 / IEC 62321-3-2

For total halogen and sulfur determination, the sample is combusted in an oxygen-rich environment, either in a combustion flask or an automated combustion unit, and the absorbed products are analyzed by ion chromatography. This approach quantifies individual elements (F, Cl, Br, I, S) with high sensitivity and is widely used to verify halogen-free declarations for electronic materials and polymer compounds.

Smoke Corrosivity — ASTM D5485 / ISO 11907

Corrosimetric methods expose clean copper targets to smoke generated under radiant heating conditions, such as in the cone corrosimeter. Metal loss measured after exposure is converted to a NaCl-equivalent deposition value, providing a direct estimate of the corrosive damage that smoke would inflict on electronics and metallic components in a real fire scenario.

Typical Acceptance Criteria

• HCl + HBr ≤ 0.5% of specimen mass per IEC 60754-1
• pH ≥ 4.3 per IEC 60754-2
• Conductivity ≤ 10 µS/mm per IEC 60754-2
• Cl ≤ 900 ppm, Br ≤ 900 ppm, Cl + Br ≤ 1500 ppm per IEC 61249-2-21 for halogen-free laminates
• Smoke density limits per IEC 61034 or ASTM E662 where a full LSZH declaration is required

Applications

Corrosive gas analysis results feed directly into material qualification, product certification, and fire-safety engineering across a broad range of industries.

• Rail transit: qualification of cables and interior materials under EN 45545-2 and EN 50305, where limited smoke and corrosivity are mandatory for rolling stock and underground lines
• Marine and offshore: selection of cable sheaths, insulation, and interior fittings that minimize acid smoke in confined compartments
• Data centers and telecom facilities: protection of high-value server and switching hardware from secondary smoke damage through specification of LSZH cabling and enclosures
• Tunnels and metro infrastructure: corrosion-resistant materials that reduce post-fire structural damage and accelerate reopening of underground spaces
• Power plants, substations, and nuclear facilities: verification that cable and coating materials will not disable safety-critical instrumentation during fire events
• Electronics and electrical equipment: halogen-free verification of PCB laminates, connectors, and housings per IEC 61249-2-21 and buyer specifications
• Building and construction: demonstration of low-corrosivity performance for public buildings, airports, and mass-transit stations

FAQ

Which plastics generate the most corrosive combustion gases?

PVC is the most significant source of hydrogen chloride, releasing HCl on the order of half of its own mass when it burns. Brominated and chlorinated flame retardants evolve HBr and HCl respectively, fluoropolymers such as PTFE can release hydrogen fluoride, and sulfur-cured rubbers produce sulfur dioxide. Halogen-free polyolefins, by contrast, chiefly generate carbon dioxide, carbon monoxide, and water, with comparatively low acidity.

What is the difference between IEC 60754-1 and IEC 60754-2?

Part 1 specifically quantifies the combined halogen acid gases (HCl + HBr) trapped during combustion, reported as a mass percentage of the sample, and is the definitive test for halogen-related corrosivity. Part 2 measures the overall acidity of all combustion products by pH and the total ionic content by conductivity of the absorption water, thereby also capturing corrosive contributions from sulfur and phosphorus species.

What limits must a material meet to be called low-smoke zero-halogen?

Exact requirements vary by specification, but the most widely applied criteria are HCl + HBr content ≤ 0.5% per IEC 60754-1, pH ≥ 4.3 and conductivity ≤ 10 µS/mm per IEC 60754-2, together with smoke density limits measured under IEC 61034 or ASTM E662. Some railway and marine specifications add explicit fluorine and sulfur limits.

How much sample is required and how are specimens prepared?

Typically only a few grams of material are needed. Specimens are granulated to the particle size required by the applicable standard, conditioned, and weighed into quartz combustion boats. Cable compounds are usually submitted in granule or strip form, and finished components can be cryo-milled to obtain a representative sample.

Does passing IEC 60754 guarantee that a material is safe in a fire?

No. Corrosive gas analysis addresses only one aspect of fire hazard. A complete fire-risk assessment also considers ignitability, flame spread, heat release, smoke density, and smoke toxicity, which are evaluated under separate standards such as ISO 5660-1, ISO 5659-2, and EN 45545-2. Halogen-free materials can still produce significant smoke or carbon monoxide.

Can corrosive gas analysis support halogen-free product declarations?

Yes. Combustion corrosivity data, combined with total halogen results from combustion ion chromatography, form the technical basis for halogen-free labeling of cables, connectors, and laminates. These results are routinely submitted to accredited third-party laboratories for independent verification during product certification.