1. Purpose
The Vertical Burning Tester (also known as the Vertical Flame Tester) is a precision instrument used to evaluate the flammability of plastics, textiles, and automotive materials.
This calibration procedure ensures the accuracy, reliability, and repeatability of test results according to international standards such as UL 94, ASTM D3801, and ISO 9772.
2. Calibration Objectives
Verify that the burner, frame, timing device, and test chamber meet standard specifications.
Ensure accurate control of flame height, gas flow rate, sample distance, and ignition duration.
Maintain test result consistency and traceability in compliance with laboratory quality systems (ISO/IEC 17025).
3. Calibration Items and Methods
| Calibration Item | Description | Method |
|---|---|---|
| Flame Height and Burner Structure | Check that the flame height (typically 20 mm or 125 mm, depending on the standard) and blue cone shape meet requirements. | Measure flame height with a flame height gauge; verify gas pressure and flow rate with a calibrated flowmeter. |
| Specimen Holder and Frame Geometry | Confirm that the sample holder is correctly aligned, and the distance between the burner and specimen matches standard values. | Use a steel ruler and angle gauge to measure spacing and verticality. |
| Timing Device | Verify the accuracy of after-flame and after-glow time measurement. | Compare against a reference electronic timer; perform multiple time interval checks (10 s, 20 s, 30 s). |
| Temperature and Ambient Conditions | Ensure environmental temperature and humidity are within the allowable range. | Record with calibrated thermohygrometer. |
| Exhaust and Ventilation System | Verify airflow is stable and does not interfere with the flame. | Inspect ventilation and measure airflow speed; confirm no cross-draft. |
| Safety and Instrument Integrity | Ensure the test chamber is clean, transparent, leak-free, and structurally sound. | Visual inspection and gas leak test; confirm stable ignition. |
4. Calibration Procedure
Perform a preliminary inspection with the tester in a cold state (no combustion).
Ignite the burner and adjust gas flow to achieve the required flame height.
Use calibration tools (flame height gauge, timer, angle meter) to check all parameters.
Conduct a trial test to verify flame stability and timing accuracy.
Record all data including ambient conditions, gas flow rate, and measurement deviations.
Issue a calibration report specifying the instrument model, calibration date, responsible technician, and pass/fail results.
If deviations exceed allowable limits, adjust or repair components and repeat the calibration.
5. Calibration Frequency and Tolerance
Full calibration should be performed annually; for frequent use or critical testing environments, every 6 months is recommended.
Recalibration is required after instrument relocation, gas replacement, or burner maintenance.
Typical allowable deviations:
Flame height: ±1 mm
Timer accuracy: ±0.5 s
Gas flow rate: ±5%
6. Documentation and Traceability
Calibration records must be retained for at least two years or per laboratory quality system requirements.
All calibration instruments (timers, gauges, flowmeters) should be traceable to national or international standards.
A daily functional check (flame height, timer, sample holder alignment) should be performed before each test session.
7. Applicable Standards
UL 94: Tests for Flammability of Plastic Materials
ASTM D3801: Vertical Burning Test for Plastics
ISO 9772 / ISO 9773: Determination of Burning Behavior
FMVSS 302: Automotive Interior Material Flammability
GB/T 2408: Vertical Burning Test Standard (China)
