🎯 Objective
To determine the flash point and fire point of a given oil sample using Pensky Martin's closed cup apparatus.
📖 Principle / Theory
When a flammable liquid is heated, it gives off vapours. The Flash Point is the lowest temperature at which the vapour of the liquid momentarily ignites (flashes) when a flame is applied — but the burning does not continue.
The Fire Point is the temperature at which the vapour continues to burn for at least 5 seconds after the test flame is applied.
Pensky Martin's closed cup apparatus minimises interference from surrounding air currents and is used for oils with flash point > 50°C (e.g., diesel, lubricating oils).
Low flash point = more flammable = greater fire hazard.
🧰 Apparatus Required
Pensky Martin's closed cup apparatus, thermometer (0–400°C), heating mantle, pilot flame.
🧪 Chemicals Required
Given oil sample (diesel / lubricating oil / kerosene), acetone (for cleaning).
⚗️ Procedure
- Clean the Pensky Martin's cup thoroughly with acetone and allow to dry.
- Fill the oil sample to the mark on the inner cup. Fit the lid with shutter and thermometer.
- Heat the oil slowly at a rate of 5–6°C per minute with stirring.
- At every 2°C rise, open the shutter momentarily and apply the test flame.
- Note the temperature at which a momentary blue flame appears — this is the FLASH POINT.
- Continue heating. Note the temperature at which the oil ignites and burns continuously for ≥ 5 seconds — this is the FIRE POINT.
- Note both values. Repeat for confirmatory readings.
📊 Observations & Calculations
| Observation | Trial 1 | Trial 2 | Trial 3 |
|---|---|---|---|
| Initial burette reading (mL) | ______ | ______ | ______ |
| Final burette reading (mL) | ______ | ______ | ______ |
| Volume of titrant used (mL) | ______ | ______ | ______ |
| Concordant volume (mL) | ______ | ||
Volume of titrant (V) = ______ mL
Result = ______ (using appropriate formula)
✅ Result
Flash Point of the given oil = ______°C. Fire Point = ______°C. The oil is classified as a [flammable / combustible] liquid.
⚠️ Precautions
- Maintain slow, steady heating rate (5–6°C/min). Rapid heating gives inaccurate results.
- Keep away from flammable materials during the experiment.
- Apply the test flame for only 1 second at each test temperature.
- Do not lean over the apparatus; a flash can occur unexpectedly.
- Keep a fire extinguisher (CO₂ type) nearby.
- The thermometer must be calibrated and properly positioned.
❓ Viva-Voce Questions
📚 References
- IS 1448 (P:21) – Methods of Test for Petroleum Products: Flash Point (Pensky Martin)
- Rattan, S. – Engineering Chemistry, Arihant Publication