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D5207-20 – Standard Test Method Technical Guide
🛠️ Scope and Summary of Practice
ASTM D5207-20 establishes a standardized procedure for confirming the heat output of the 20‑mm (50 W) and 125‑mm (500 W) test flames employed in small‑scale burning tests on plastic materials. Under the jurisdiction of ASTM Committee D20 on Plastics, this practice relies on the laboratory burner defined in Specification D5025 and specifies back pressures and flow rates for methane, propane, and butane supply gases. The purpose is to ensure that two different burner/gas combinations produce an identical thermal impact on the specimen.
The practice measures the response of materials to heat and flame under controlled laboratory conditions. It does not by itself incorporate all factors required for fire hazard or risk assessment under actual fire conditions. Users must consult the full standard for the complete list of referenced documents, including Terminology D883 and E176, which provide essential definitions for plastics and fire testing terminology.
🔥 Flame Configurations and Gas Supply Parameters
Two standard test flame configurations are defined: the 20‑mm (50 W) flame and the 125‑mm (500 W) flame. Before the heat‑evolution confirmation is performed, the operator must verify that the flame is burning steadily with the correct height and a clear blue color. The standard provides distinct back pressures and volumetric flow rates for methane, propane, and butane to achieve these conditions. Table 1 summarizes the target parameters and acceptance limits for confirming the test flames.
| 🔥 Flame Type | 🌡️ Power Output | 💨 Primary Gas | ⚙️ Back Pressure / Flow Rate | 📐 Rise Time Target (100→700 °C) |
|---|---|---|---|---|
| 20‑mm Flame | 50 W | Methane | ~0.5 kPa / ~105 mL·min⁻¹ | 44 s (acceptance: 40–48 s) |
| 125‑mm Flame | 500 W | Methane | ~10 kPa / ~965 mL·min⁻¹ | 54 s (acceptance: 50–60 s) |
| Alternate Fuel Gases | Propane / Butane | Specified lower flow rates (higher calorific value) | Same rise‑time targets (ensures identical heat evolution) | |
💡 Technical Note: The acceptance criterion for flame confirmation is strictly the time required for the thermal sensor to heat from 100 °C to 700 °C. Exact flow rates may vary slightly with gas purity and burner condition, but the measured rise time must fall within the specified window for the flame to be considered valid for testing.
🌡️ Heat‑Evolution Confirmation Procedure
The confirmation process evaluates the heat‑evolution profile of the established flame. After the correct flame height and color are obtained, a thermal sensor is positioned over the flame. The sensor consists of a mineral‑insulated, metal‑sheathed base‑metal thermocouple conforming to ASTM E608, calibrated per ASTM E220 and referenced to the emf tables of ASTM E230.
Once positioned, the time for the thermocouple temperature to increase from 100 °C to 700 °C is determined. This time measurement confirms that the flame heat output is within the required tolerance for the specific test flame. Table 2 outlines the key equipment requirements for the procedure.
| ⚙️ Component | 📋 Specification / Requirement |
|---|---|
| Laboratory Burner | ASTM D5025 design (Bunsen‑type, specific barrel dimensions, air inlet openings) |
| Thermocouple Sensor | Mineral‑insulated, metal‑sheathed base‑metal type per ASTM E608 |
| Calibration | Calibrated per ASTM E220 using the standard emf values of ASTM E230 |
| Timing Device | Accurate to ±0.1 s over the duration of the rise |
| Test Gas Supply | Methane (≥98 % purity), or technical‑grade propane/butane |
The rise time is typically measured several times to ensure repeatability. If the recorded time deviates from the acceptance criteria, the gas pressure and flow settings must be adjusted, and the burner or thermocouple inspected for damage or improper alignment.
⚠️ Fire Testing Safety: As stated in Section 1.4 of the standard, fire testing is inherently hazardous. Adequate safeguards for personnel and property shall be employed in conducting these tests. Users are responsible for establishing appropriate safety, health, and environmental practices in accordance with regulatory limitations.
❓ Frequently Asked Questions
🔍 Why is flame confirmation necessary for small‑scale burning tests?
Flame confirmation guarantees that the heat‑evolution profile of the test flame is consistent and reproducible. Variations in gas composition, burner cleanliness, or ambient conditions can alter flame severity. The procedure ensures that the flame delivering heat to the test specimen meets the precise energy requirements of the referenced test method, allowing valid comparisons between laboratories.
💡 What gases are acceptable for use with ASTM D5207?
The standard explicitly provides back pressures and flow rates for three fuel gases: methane, propane, and butane. While methane is the most common gas for standards such as UL 94, propane and butane are allowed provided their flow rates are adjusted per the standard’s tables and the flame is confirmed via the 100 °C to 700 °C thermal sensor rise test.
⚡ What is the specific acceptance criterion for the rise time?
For the 20‑mm (50 W) flame, the sensor must reach 700 °C from 100 °C in 44 ± 4 seconds. For the 125‑mm (500 W) flame, the required time is 54 ± 6 seconds (typically 50–60 s). If the measured time does not fall within this acceptance window, the flame configuration is considered invalid for testing.
📌 How often should the flame confirmation procedure be performed?
While the standard does not prescribe a fixed schedule, established laboratory practice requires confirmation whenever a gas cylinder is changed, the burner is cleaned or replaced, or at the beginning of each test day. Any noticeable change in flame appearance—height, color, or stability—should immediately trigger a re‑confirmation.