Flash Point

Detailed Description

The flash point is the lowest temperature at which a liquid generates sufficient vapor to form an ignitable mixture with air near the surface of the liquid. At the flash point, the vapor may ignite if an ignition source is present, but the flame will not sustain itself without the continued application of heat.

Key concepts related to flash point include:

Flash point vs. fire point: The flash point is the temperature at which a momentary flash occurs, while the fire point (typically a few degrees higher) is the temperature at which sustained combustion occurs.
Closed cup vs. open cup: Flash points can be measured using closed cup methods (vapor contained) or open cup methods (vapor exposed to air), with closed cup values typically lower.
Lower flammable limit (LFL): At the flash point, the concentration of vapor in air is at or above the LFL, the minimum concentration needed for ignition.
Pressure dependence: Flash point varies with pressure; higher pressures generally result in higher flash points.

The flash point of a substance is influenced by several factors:

Volatility: More volatile substances generally have lower flash points.
Chemical structure: The molecular structure affects vapor pressure and thus flash point.
Purity: Impurities can significantly alter the flash point of a substance.
Mixture composition: For mixtures, the component with the lowest flash point often dominates, though interactions can be complex.

Importance in Safety Data Sheets

The flash point is one of the most critical safety parameters in an SDS for several reasons:

Fire hazard assessment: Primary indicator of a liquid's fire hazard and flammability classification.
Storage requirements: Determines appropriate storage conditions, including temperature controls and fire protection needs.
Handling procedures: Informs safe handling practices, including ventilation requirements and ignition source controls.
Transportation regulations: Critical for determining transportation hazard classes and packaging requirements.
Emergency response: Essential information for firefighters and emergency responders.
Regulatory compliance: Used for classification under GHS, NFPA, and other hazard communication systems.

Measurement Methods

Several standardized methods are used to determine flash points:

Method	Description	Typical Applications
Pensky-Martens Closed Cup (PMCC)	ASTM D93, ISO 2719: Sample is heated in a closed cup with intermittent stirring and an ignition source is introduced periodically	Viscous liquids, petroleum products, paints, varnishes
Tag Closed Cup (TCC)	ASTM D56: Sample is heated in a closed cup without stirring and an ignition source is introduced periodically	Liquids with viscosity less than 5.5 mm²/s at 40°C, excluding petroleum products
Abel Closed Cup	IP 170, ISO 13736: Similar to TCC but with different dimensions and procedure	Low flash point liquids (below 70°C), especially petroleum products
Small Scale Closed Cup (SSCC)	ASTM D3828, ISO 3679: Uses small sample volumes with rapid temperature equilibration	Limited sample quantities, rapid testing
Cleveland Open Cup (COC)	ASTM D92, ISO 2592: Sample is heated in an open cup and an ignition source is passed over the surface	High flash point materials, residual fuel oils, lubricants
Setaflash Closed Cup	ASTM D3278, ISO 3679: Rapid equilibrium method using a small sample size	Paints, varnishes, limited sample quantities

Flash Point Testing Apparatus

Pensky-Martens Closed Cup

Features a closed cup with a stirrer, cover with openings for thermometer and ignition source, and controlled heating rate.

Standard: ASTM D93, ISO 2719

Temperature Range: 40°C to 360°C

Tag Closed Cup

Features a water or air bath for temperature control, test flame applicator, and thermometer.

Standard: ASTM D56

Temperature Range: 0°C to 93°C

Cleveland Open Cup

Features an open brass test cup, heating plate, test flame applicator, and thermometer.

Standard: ASTM D92, ISO 2592

Temperature Range: 79°C to 400°C

Setaflash Closed Cup

Features a small sample cup with cover, built-in thermometer, and gas ignition source.

Standard: ASTM D3278, ISO 3679

Temperature Range: -30°C to 300°C

Flash Point and Flammability Classification

Flash point is a primary criterion for flammability classification under various regulatory systems:

GHS Classification for Flammable Liquids

Category	Criteria	Examples
Category 1	Flash point < 23°C and initial boiling point ≤ 35°C	Diethyl ether, pentane
Category 2	Flash point < 23°C and initial boiling point > 35°C	Acetone, ethanol, gasoline
Category 3	Flash point ≥ 23°C and ≤ 60°C	Kerosene, diesel fuel, turpentine
Category 4	Flash point > 60°C and ≤ 93°C	Mineral oil, some lubricating oils

Other Classification Systems

System	Classification	Flash Point Criteria
NFPA 704	Flammability Rating 4	Flash point < 23°C
NFPA 704	Flammability Rating 3	Flash point ≥ 23°C and < 38°C
NFPA 704	Flammability Rating 2	Flash point ≥ 38°C and < 93°C
NFPA 704	Flammability Rating 1	Flash point ≥ 93°C
DOT (US)	Flammable Liquid	Flash point ≤ 60°C
DOT (US)	Combustible Liquid	Flash point > 60°C and < 93°C
OSHA (US)	Flammable Liquid	Flash point < 93°C

Substance	Flash Point (°C)	Method	GHS Category
Acetone	-20	Closed cup	2
Ethanol	13	Closed cup	2
Isopropyl alcohol	12	Closed cup	2
Toluene	4	Closed cup	2
Xylene	27	Closed cup	3
Diesel fuel	52-96	Closed cup	3 or 4
Kerosene	38-72	Closed cup	3 or 4
Mineral oil	135-210	Open cup	Not classified
Vegetable oil	327	Open cup	Not classified
Diethyl ether	-45	Closed cup	1

Safety Considerations

Understanding flash point is critical for safety for several reasons:

Ignition risk assessment: Materials with flash points at or below ambient temperature present immediate fire hazards in normal conditions.
Vapor accumulation: Even if the bulk liquid is below its flash point, localized heating or poor ventilation can create ignitable vapor concentrations.
Process safety: Operations involving heating of flammable liquids require special precautions when approaching the flash point.
Static electricity: Low flash point liquids are particularly susceptible to ignition from static discharges.
Hot work permits: Flash point information is essential when determining safe conditions for hot work near flammable liquids.
Fire suppression: Different fire suppression strategies may be required based on flash point and other properties.

Regulatory Requirements

According to GHS and various regional regulations (EU CLP, US OSHA HazCom, etc.), the flash point should be indicated in Section 9 of the Safety Data Sheet as part of the description of basic physical and chemical properties. This information is considered mandatory for liquids with flash points ≤ 93°C, though it may be reported as "not applicable" for solids or non-flammable liquids.

Additionally, the test method used to determine the flash point should be specified, as different methods can yield different results for the same substance.

Best Practices

When reporting flash points in an SDS:

Specify the temperature in degrees Celsius (°C) and optionally in other units (e.g., Fahrenheit)
Indicate the test method used (e.g., closed cup, open cup) and the specific standard if known (e.g., ASTM D93)
For substances with very low flash points, it may be appropriate to indicate "
For substances with very high flash points, it may be appropriate to indicate ">X°C" if the exact value is above the upper limit of the test method
For mixtures with variable composition, provide a range if appropriate
Note if the substance decomposes before reaching its flash point
For non-flammable substances, clearly indicate "not applicable" rather than leaving the field blank
Ensure consistency between the flash point and the flammability classification in Section 2 of the SDS