Pensky-Martens Flashpoint Tester

Fully Automated Pensky-Martens Flashpoint Tester (PMA-4)

ASTM D93

lab-equipment04

Every liquid has a vapor pressure, which is a function of that liquid’s temperature. As the temperature increases, the vapor pressure increases. As the vapor pressure increases, the concentration of vapor of the flammable liquid in the air increases. Hence, temperature determines the concentration of vapor of the flammable liquid in the air.

A certain concentration of vapor in the air is necessary to sustain combustion, and that concentration is different for each flammable liquid. The flash point of a flammable liquid is the lowest temperature at which there will be enough flammable vapor to ignite when an ignition source is applied.

There are two basic types of flash point measurement: open cup and closed cup. In open cup devices the sample is contained in an open cup which is heated, and at intervals a flame is brought over the surface. The measured flash point will actually vary with the height of the flame above the liquid surface, and at sufficient height the measured flash point temperature will coincide with the fire point. The best known example is the Cleveland open cup (COC).

There are two types of closed cup testers: non-equilibrium, such as Pensky-Martens where the vapors above the liquid are not in temperature equilibrium with the liquid, and equilibrium, such as Small Scale (commonly known as Setaflash) where the vapors are deemed to be in temperature equilibrium with the liquid. In both these types the cups are sealed with a lid through which the ignition source can be introduced. Closed cup testers normally give lower values for the flash point than open cup (typically 5-10°C lower, or 9-18 °F lower) and are a better approximation to the temperature at which the vapor pressure reaches the lower flammable limit.

The flash point is an empirical measurement rather than a fundamental physical parameter. The measured value will vary with equipment and test protocol variations, including temperature ramp rate (in automated testers), time allowed for the sample to equilibrate, sample volume and whether the sample is stirred.

Methods for determining the flash point of a liquid are specified in many standards. For example, testing by the Pensky-Martens closed cup method is detailed in ASTM D93, IP34, ISO 2719, DIN 51758, JIS K2265 and AFNOR M07-019. Determination of flash point by the Small Scale closed cup method is detailed in ASTM D3828 and D3278, EN ISO 3679 and 3680, and IP 523 and 524.


Why we need to know?

  • The flash point of a volatile material is the lowest temperature at which it can vaporise to form an ignitable mixture in air. Measuring a flash point requires an ignition source. At the flash point, the vapor may cease to burn when the source of ignition is removed.
  • The flash point is not to be confused with the auto ignition temperature, which does not require an ignition source, or the fire point, the temperature at which the vapor continues to burn after being ignited. Neither the flash point nor the fire point is dependent on the temperature of the ignition source, which is much higher.
  • The flash point is often used as a descriptive characteristic of liquid fuel, and it is also used to help characterise the fire hazards of liquids. “Flash point” refers to both flammable liquids and combustible liquids. There are various standards for defining each term. Liquids with a flash point less than 37.7°C – depending upon the standard being applied are considered flammable, while liquids with a flash point above those temperatures are considered combustible.


Flash Point for General Oil (Closed Cup):


General Oil

Flash Point (°C)

Base Oil

210

Bunker Fuel

> 200

Diesel

60 – 75

Heavy Oil

150 – 200

Light Fuel Oil 80 cSt

62 – 88

Medium Fuel Oil 180 cSt

62 – 88 

Tyre Oil

< 30

Waste Engine Oil

40 – 210

Pentas Flora Recovered Oil

Flash Point (°C)

Eco Light Fuel Oil

40 – 50

Super Light Fuel Oil

40 – 60

Green Light Fuel Oil

70 – 80

Base Light Fuel Oil

130 – 150

Recovered Oil Specification by DOE

37.7 and above