Plastic Smoke Density Tester F313，ISO 5659.2-2006

In the field of fire safety and evaluation of fire-retardant performance of materials, smoke density testing is a critically important method. Its core purpose is to simulate, under laboratory conditions, the smoke characteristics produced by materials during combustion or high-temperature decomposition, and to quantitatively assess the impact of smoke on visibility and associated safety risks. This is of great significance for industries such as building materials, electrical cables, plastic products, transportation interior components, and aerospace, particularly in product design, risk assessment, regulatory compliance, and safety certification.

Smoke density testing is not a single experimental method. Instead, it encompasses multiple standards and testing systems. Depending on material type, service environment, and the specific performance parameters to be evaluated, different standards and test procedures may be applied. The essence of the test lies in measuring the amount of smoke generated when a material is exposed to a heat source (sometimes including an open flame), and using optical measurements to evaluate the smoke’s ability to obscure visible light, thereby inferring its effect on visibility along evacuation routes.

Basic Concept of Smoke Density Testing

“Smoke density” generally refers to the ability of smoke particles to block light. Smoke itself is a mixture of fine solid particles and liquid droplets suspended in air, produced during combustion or thermal decomposition. These particles absorb and scatter light, causing a reduction in light intensity as it passes through the smoke and resulting in reduced visibility. Therefore, smoke density testing typically uses optical measurement methods. By measuring the attenuation of a light beam passing through a smoke-filled, enclosed test chamber, the concentration of smoke can be quantified.

Core test results usually include:

Smoke Density Rating (SDR): An assessment of the overall smoke density level over a specified period.

Maximum Smoke Density (Ds max): The highest smoke density value recorded during the entire test.

Smoke Production Rate (SPR): The rate at which smoke concentration changes over time.

Light Transmittance–Time Curve (T–t Curve): A curve showing changes in light transmittance over time, used to analyze the dynamic smoke generation process.

These quantitative indicators allow for a scientific evaluation of the smoke intensity produced by materials under fire conditions. This is particularly important for evacuation safety, as dense smoke often poses a greater threat than flames themselves by causing poisoning and suffocation.

Core Principles of Smoke Density Testing

The fundamental principle of smoke density testing is to pass a light beam through a smoke-filled space generated inside a sealed test chamber and calculate the optical density of the smoke by measuring changes in light intensity before and after transmission. The test generally includes the following steps:

Sample Preparation: Test specimens are selected and prepared according to standard-specified dimensions and quantities. Different standards impose different requirements on sample size and preconditioning.

Test Chamber Sealing and Heat Source Preparation: The sample is placed inside a sealed test chamber equipped with a light source and optical sensors. Depending on the standard, a specific heat source is used; some standards require open-flame exposure, while others use radiant heating.

Optical Measurement: Once the test begins, light emitted from the source passes through the smoke in the chamber and is detected by photoelectric sensors. As smoke is generated and accumulates, absorption and scattering reduce the transmitted light intensity. The system calculates optical density based on these changes.

Data Recording and Analysis: Throughout the test, the system continuously records light transmittance, calculates smoke density ratings and maximum smoke density values, and generates time-based smoke development curves.

Test results are typically presented in the form of smoke density curves and peak density values, which are used to determine whether the fire safety performance of a material meets relevant standards.

Common Smoke Density Test Standards

Multiple standards are used worldwide for smoke density testing across different application areas. Some of the most widely adopted standards include:

ASTM E662

ASTM E662. titled Specific Optical Density of Smoke Generated by Solid Materials, is one of the most widely used standards. It determines smoke density by measuring the obscuration of a light beam in a closed test chamber. The test includes both non-flaming (thermal decomposition) and flaming combustion modes, with smoke density recorded at various time intervals. Results are expressed as specific optical density values and are commonly used in aviation, construction, and rail transportation industries.

EN ISO 5659-2

EN ISO 5659-2 applies to smoke density testing of plastic materials and measures the optical density of smoke generated under fixed radiant heat exposure conditions. This standard is particularly suitable for evaluating smoke production from plastics in fire scenarios and is widely referenced in regulations for building, rail, and marine transportation materials.

ASTM D2843

ASTM D2843 is a test method for measuring smoke density produced by plastics during combustion or decomposition. Originally developed to evaluate the smoke-obscuring characteristics of plastic materials under fire conditions, it generates two key indices: maximum smoke generation and smoke density rating. This method is also accepted in some building codes, particularly for evaluating transparent or translucent plastics used in light-transmitting applications.

Smoke Index in ASTM E84 Tunnel Test

ASTM E84 requires materials to be installed in a tunnel furnace to evaluate flame spread and smoke development. The results include the Smoke Developed Index (SDI), which represents the smoke density performance of materials under flame propagation conditions. This is a classic standard in the fire evaluation of building materials.

EN 61034-2 / GB/T 17651.2

For cable products, EN 61034-2 and GB/T 17651.2 define methods for measuring smoke density generated during cable combustion under specified conditions. These tests form part of cable fire performance classification and are especially important for evaluating fire risks in wiring systems and visibility in evacuation routes.

Application Scenarios of Smoke Density Testing

Smoke density testing has broad practical applications, particularly in fire safety assessment and mandatory compliance testing.

Building Materials Safety Evaluation

Smoke generation from building materials during a fire is critical, as smoke severely affects evacuation visibility and may cause respiratory injury. Smoke density testing of wall panels, flooring, ceilings, and insulation materials provides guidance for material selection in different building areas and supports compliance with fire safety regulations.

Transportation Industry

In aviation, rail transit, and maritime industries, smoke density testing of interior materials such as carpets, seat materials, and panels is a mandatory safety requirement. Dense smoke can hinder passenger evacuation and cause toxic exposure, especially in enclosed spaces. Many industry regulations reference ASTM E662 or ISO 5659-2 to evaluate smoke generation characteristics.

Cables and Wiring Products

Cables can act as pathways for fire spread, and smoke generated by burning insulation materials can significantly impact evacuation safety. Measuring cable smoke density according to EN 61034-2 or GB/T 17651.2 provides a basis for fire rating classification and regulatory compliance.

Plastic Products and Consumer Materials

Plastics are widely used in electronics, household appliances, and consumer goods. During high-temperature decomposition or combustion, plastics may produce large amounts of smoke. Smoke density testing helps assess product safety and ensures compliance with regulatory limits on smoke generation.

Significance of Test Indicators and Interpretation of Results

Smoke density testing not only provides quantitative data on smoke concentration but also reflects several critical safety characteristics:

Optical Density and Visibility

Measured optical density values are inversely related to visibility. Higher smoke density means greater light absorption and scattering, resulting in severely reduced visibility during real fires and making evacuation routes harder to identify. This is the core safety indicator of the test.

Maximum Smoke Density and Time Dynamics

Maximum smoke density represents the peak smoke concentration during testing, while the smoke production rate curve shows how smoke concentration evolves over time. These indicators are especially important for analyzing early-stage fire behavior, when rapid visibility loss poses the greatest danger.

Comprehensive Indicators such as SDR and SDI

Composite indicators such as Smoke Density Rating (SDR) or Smoke Developed Index (SDI) allow comparison of different materials and test conditions. For example, the SDI in ASTM E84 is used alongside flame spread index to rate the overall fire performance of interior finishing materials.

Importance of Smoke Density Testing to Fire Safety

In fire safety assessment, smoke often presents a greater hazard than flames themselves because:

Visibility deteriorates rapidly, obscuring evacuation routes.

Smoke may contain toxic gases, increasing the risk of poisoning.

Corrosive or acidic components in smoke can severely damage equipment.

Through scientific smoke density testing, potential risks can be identified during the product development stage, enabling optimization of material selection, product design, and protective measures, while also supporting regulatory compliance testing.

Technological Development Trends and Future Directions

As fire safety standards continue to evolve and understanding of smoke generation deepens, smoke density testing technology is also advancing:

More refined data analysis: The use of optical sensors and image recognition technologies to capture finer-grained smoke dynamics in real time.

Cross-standard integrated evaluation: Combining indicators from different test standards to provide multi-dimensional safety assessments, such as evaluating smoke density together with toxicity.

Simulation of real fire scenarios: Integrating experimental testing with virtual fire simulations to better correlate laboratory data with real-world fire behavior and improve practical guidance.

Smoke density testing is an indispensable component of fire safety evaluation. By quantifying smoke concentration and its light-obscuring effects during combustion or thermal decomposition, it provides a scientific basis for design verification, risk assessment, and regulatory compliance of building materials, cables, plastic products, and transportation interior materials. As standards improve and testing technologies advance, smoke density testing will continue to play a vital role in safeguarding public safety and enhancing fire performance of products.