Flammability

Detailed Description

Flammability is the ability of a substance to burn or ignite, causing fire or combustion. In the context of a Safety Data Sheet (SDS), flammability is a critical safety property that indicates how easily a material can ignite and sustain combustion under specified conditions.

The combustion process requires three elements, often depicted as the "fire triangle":

Fuel: The flammable substance itself
Oxygen: Typically from air
Heat/Ignition source: Energy to initiate the reaction

Key concepts related to flammability include:

Flammable range: The concentration range in air between the lower flammable limit (LFL) and upper flammable limit (UFL) within which a substance can ignite and sustain combustion.
Flash point: The lowest temperature at which a liquid produces sufficient vapor to form an ignitable mixture with air.
Auto-ignition temperature: The minimum temperature required for self-sustained combustion without an external ignition source.
Burning rate: The speed at which combustion propagates through a material.
Heat of combustion: The energy released when a substance undergoes complete combustion.

Importance in Safety Data Sheets

Flammability information in an SDS is critical for several reasons:

Hazard classification: Determines the material's fire hazard classification under GHS and other regulatory systems.
Risk assessment: Enables evaluation of fire and explosion risks in workplaces and processes.
Storage requirements: Informs appropriate storage conditions, including temperature controls, ventilation, and segregation from incompatible materials.
Handling procedures: Guides safe handling practices, including controls for ignition sources and static electricity.
Emergency response: Provides critical information for firefighting and spill response procedures.
Transportation regulations: Determines transportation hazard classes and packaging requirements.

Flammability Parameters

Several parameters are used to characterize flammability:

Parameter	Description	Relevance
Flash Point	Lowest temperature at which vapors ignite when exposed to an ignition source	Primary indicator for liquid flammability classification
Auto-ignition Temperature	Temperature at which a substance ignites without an external ignition source	Important for hot work permits and process safety
Lower Flammable Limit (LFL)	Minimum concentration in air needed for ignition (% by volume)	Critical for vapor hazard assessment and ventilation requirements
Upper Flammable Limit (UFL)	Maximum concentration in air that will sustain combustion (% by volume)	Important for understanding rich mixture hazards
Burning Rate	Rate at which flame propagates through a material	Indicates how quickly a fire involving the material will spread
Heat of Combustion	Energy released during complete combustion	Indicates fire intensity and potential thermal hazards
Minimum Ignition Energy (MIE)	Minimum energy required to ignite a flammable mixture	Important for static electricity and spark hazard assessment
Oxygen Index	Minimum oxygen concentration needed to support combustion	Relevant for fire-resistant materials and inert atmosphere systems

Flammability Classification

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

GHS Classification for Flammable Solids

Category	Criteria	Examples
Category 1	Burning rate test: Burning time < 45 seconds or burning rate > 2.2 mm/s AND passes wetted zone test	Certain metal powders, phosphorus, some organic powders
Category 2	Burning rate test: Burning time < 45 seconds or burning rate > 2.2 mm/s	Sulfur, naphthalene, camphor

GHS Classification for Flammable Gases

Category	Criteria	Examples
Category 1A	Flammable at 13% or less by volume in air OR flammable range ≥ 12 percentage points	Hydrogen, methane, propane
Category 1B	Flammable but not Category 1A	Ammonia, some refrigerant gases
Category 2	Flammable range in air but not Category 1	Some gas mixtures with limited flammability

Flammability Testing Methods

Test Method	Description	Applicable Materials
Flash Point Testing	Various methods (closed cup, open cup) to determine the lowest temperature at which vapors ignite	Liquids
Burning Rate Test	Measures the rate of flame propagation along a specified sample length	Solids
Bomb Calorimetry	Measures heat of combustion by burning a sample in a sealed vessel	Solids, liquids
Limiting Oxygen Index (LOI)	Determines minimum oxygen concentration needed to support combustion	Solids, especially polymers
UL 94 Vertical Burning Test	Standardized test for flammability of plastic materials	Plastics, polymers
Flammable Range Determination	Measures lower and upper flammable limits in air	Gases, vapors
Auto-ignition Temperature Test	Determines temperature at which self-ignition occurs	Liquids, gases
Dust Explosion Testing	Evaluates explosion characteristics of combustible dusts	Powders, dusts

Flammability Characteristics of Common Materials

Material	Flash Point (°C)	Auto-ignition Temp. (°C)	Flammable Range (% vol)	GHS Classification
Gasoline	-43	280-456	1.4-7.6	Flam. Liq. 1
Diesel Fuel	52-96	210-315	0.6-7.5	Flam. Liq. 3
Ethanol	13	363	3.3-19	Flam. Liq. 2
Acetone	-20	465	2.5-12.8	Flam. Liq. 2
Toluene	4	480	1.1-7.1	Flam. Liq. 2
Methane (gas)	N/A	537	5.0-15.0	Flam. Gas 1A
Hydrogen (gas)	N/A	500	4.0-75.0	Flam. Gas 1A
Sulfur (solid)	207	232	N/A	Flam. Solid 2
Wood dust	N/A	204-260	40 g/m³ (min. explosive conc.)	Combustible Dust

Factors Affecting Flammability

Several factors can influence the flammability of a substance:

Temperature: Higher temperatures generally increase flammability by increasing vapor pressure and decreasing flash point.
Pressure: Changes in pressure can affect flammable range and ignition energy requirements.
Oxygen concentration: Higher oxygen levels can expand flammable ranges and increase combustion rates.
Particle size: For solids, smaller particles (especially dusts) have greater surface area and can be more flammable.
Moisture content: Water content can inhibit ignition and combustion of many materials.
Ventilation: Air movement can affect vapor concentration and dispersion, influencing ignition likelihood.
Ignition source energy: Higher energy sources are more likely to ignite flammable materials.
Mixture composition: For mixtures, flammability can be complex and may not follow simple additive rules.

Regulatory Requirements

According to GHS and various regional regulations (EU CLP, US OSHA HazCom, etc.), flammability information must be provided in Sections 2 and 9 of the Safety Data Sheet. Section 2 includes the hazard classification and associated hazard statements, while Section 9 provides the specific physical and chemical properties related to flammability (flash point, flammable limits, etc.).

For transportation purposes, flammability classification may also determine the appropriate UN hazard class, packing group, and shipping requirements under regulations such as ADR, IMDG, and IATA.

Best Practices

When reporting flammability in an SDS:

Clearly state the GHS flammability classification and category
Provide all relevant flammability parameters (flash point, auto-ignition temperature, flammable limits)
Specify test methods used for flammability determinations
Include information on special fire hazards (e.g., formation of toxic combustion products)
Provide appropriate fire prevention and firefighting guidance in Sections 5 and 7
Ensure consistency between flammability information in different sections of the SDS
For materials that may form combustible dust, include appropriate warnings even if the bulk material is not classified as flammable
For mixtures, consider the contribution of all components to overall flammability