Smoke generated by burning cellular plastics is one of the most critical hazards in fire scenarios, as it rapidly reduces visibility and carries toxic combustion products. Determination of smoke generation quantifies the optical density and total smoke output of foamed materials under controlled flaming conditions, enabling objective fire-hazard assessment and regulatory compliance. This article outlines the principle, standards, sample requirements, test items, methods, and typical applications of smoke generation testing for cellular plastics.
Technical Overview
Cellular plastics—materials with a foamed, low-density structure such as polyurethane, polystyrene, polyethylene, and phenolic foams—are widely used in thermal insulation, packaging, cushioning, and lightweight construction. Because of their high surface-to-mass ratio and combustible polymer matrices, these materials can generate large volumes of dense smoke when ignited or exposed to radiant heat. Statistical fire investigations consistently identify smoke inhalation and loss of visibility as leading causes of fire casualties, making smoke output a primary parameter in fire-risk evaluation.
Smoke generation testing measures the attenuation of a light beam passing through smoke accumulated in a closed chamber or transported through an exhaust duct during controlled combustion of a test specimen. The measured reduction in light transmittance is converted into optical density values, from which derived indices such as smoke density rating (SDR), specific optical density (Ds), smoke production rate (SPR), and total smoke production (TSP) are calculated. Internationally recognized test standards include ASTM D2843, ASTM E662, ISO 5659-2, ISO 5660-1, GB/T 8323, GB/T 16172, and GB/T 20284, which form the technical basis for classification systems such as GB 8624 and EN 13501.
Accredited third-party laboratories perform these tests under standardized ventilation, ignition, and irradiance conditions to produce reproducible data for product certification, research and development, and fire-engineering design.
Testing Samples
Rigid and Flexible Polyurethane Foams (PU / PIR)
Polyurethane and polyisocyanurate foams used in building insulation panels, pipe insulation, and spray-foam systems. Specimens are typically cut to the standard dimensions required by the selected method (for example, 75 mm × 75 mm with specified thickness for smoke-chamber testing) and conditioned to constant mass at standard temperature and humidity.
Expanded and Extruded Polystyrene Foams (EPS / XPS)
Molded EPS board and extruded XPS board used for wall, roof, and floor insulation. Due to their thermoplastic melting and dripping behavior, specimens may require the support fixtures specified in the relevant standard to ensure consistent exposure to the ignition source.
Polyolefin and Cross-Linked Foams (PE / EVA / XLPE)
Flexible foamed sheets used in packaging, automotive interiors, sports equipment, and cushioning. These materials are tested to evaluate both flaming and smoldering smoke contribution.
Phenolic, PVC, and Melamine Foams
Thermoset or inherently flame-retarded foams used in high fire-safety applications such as duct insulation, marine panels, and acoustic components. Testing verifies the effectiveness of flame-retardant formulations in suppressing smoke production.
Composite Foam Products and Sandwich Panels
Finished products such as metal-faced insulation sandwich panels, foam-cored doors, upholstered furniture padding, and mattress layers, tested in their end-use configuration where the standard permits.
Testing Items
Depending on the selected standard and the purpose of the evaluation, the following parameters are typically reported:
- Light transmittance (%) of the accumulated smoke at defined test times
- Optical density (OD) and average optical density over the exposure period
- Specific optical density: Ds, Ds(4 min), and maximum specific optical density (Ds max) per ASTM E662 and ISO 5659-2 / GB/T 8323
- Smoke Density Rating (SDR), a 0–100 index per ASTM D2843, commonly limited to 75 or lower in many building-code applications
- Smoke Production Rate (SPR) and Total Smoke Production (TSP) determined by cone calorimetry per ISO 5660-1 / GB/T 16172
- Smoke growth rate index (SMOGRA) and FIGRA-based smoke classification per GB/T 20284 / EN 13823
- Mass loss and specimen mass-loss rate, providing correlation between decomposition behavior and smoke yield
Testing Methods
Smoke Density Chamber Method (ASTM D2843 / ISO 5659-2 / GB/T 8323)
A horizontally supported specimen is exposed to a standardized propane burner flame inside a sealed chamber of defined volume. A vertical light path from a photometric source to a detector passes through the accumulating smoke. Transmittance is recorded continuously, and the Smoke Density Rating is calculated from the area under the transmittance–time curve. ISO 5659-2 and GB/T 8323 additionally allow radiant heating with or without pilot ignition and report Ds max and vomax values.
NBS Smoke Chamber Method (ASTM E662)
A vertical specimen is exposed either to a radiant heat source alone (smoldering/non-flaming mode) or to radiant heat combined with a pilot flame (flaming mode). Specific optical density Ds is calculated from measured transmittance, chamber geometry, and specimen exposed area, yielding comparative smoke data for screening materials.
Cone Calorimeter Method (ISO 5660-1 / GB/T 16172)
A 100 mm × 100 mm specimen is exposed to a defined radiant flux (commonly 25, 35, or 50 kW/m²) in an open, ventilated configuration. Smoke is quantified by a laser photometer in the exhaust duct, yielding smoke production rate and total smoke release alongside heat release rate, ignition time, and mass loss. This method provides data suitable for fire modeling and performance-based design.
Single Burning Item (SBI) Method (GB/T 20284 / EN 13823)
For products intended for the European and Chinese building-material classification systems, a corner-mounted specimen assembly is exposed to a main burner, and smoke production is determined from duct measurements. The SMOGRA index contributes to the smoke classes s1, s2, or s3 under GB 8624 and EN 13501.
For all methods, specimens must be conditioned to equilibrium in a controlled atmosphere, mounted in the prescribed orientation, and tested with calibrated photometric systems, ignition sources, and radiant heaters to ensure metrological traceability and interlaboratory reproducibility.
Applications
Smoke generation data for cellular plastics directly support the following applications:
- Building-product fire classification and certification under GB 8624, EN 13501, and regional building codes requiring limits on SDR, Ds max, or smoke classes
- Material selection for thermal insulation systems, sandwich panels, air-duct linings, and façade assemblies where escape-route visibility is a design criterion
- Flame-retardant formulation development and comparative screening of PU, PIR, EPS, XPS, and phenolic foam systems
- Quality control in foam manufacturing, verifying consistency between production lots and qualified formulations
- Compliance demonstration for transportation interiors, furniture, mattresses, and appliances governed by sector-specific smoke requirements
- Input data for fire-risk analysis, egress simulation, and performance-based fire safety engineering
FAQ
What is an acceptable smoke density result?
Acceptance limits depend on the jurisdiction and application. Under many building-code references to ASTM D2843, a maximum Smoke Density Rating of 75 is common, while GB 8624 imposes graded smoke limits based on the product class and the applicable test route. The specification of the purchaser or regulator should always be consulted.
Why are both flaming and non-flaming (smoldering) modes tested?
Some materials produce more smoke when thermally decomposing without flame than when burning openly. Testing both exposure modes, as provided in ASTM E662 and ISO 5659-2, captures the full range of smoke behavior a product may exhibit in a real fire.
How do melting and dripping of thermoplastic foams affect testing?
EPS, XPS, and polyolefin foams may melt, flow, or drip during exposure, altering the exposed area and burning regime. Standards specify support grids, specimen thicknesses, and mounting practices to standardize this behavior, and deviations must be documented in the test report.
What is the typical test duration and reporting time?
Chamber tests typically run 4 to 10 minutes of active exposure per specimen, with replicate determinations required by most standards. Full reporting, including conditioning, calibration, and documentation, is generally completed within one to two weeks by accredited third-party laboratories.
Can smoke results from different methods be compared directly?
No. Each method uses distinct exposure conditions, chamber or duct geometry, and calculation bases. Data are only comparable within the same standard and test configuration, which is why classification systems specify the exact method to be used for each product category.