Explosive Properties

Detailed Description

Explosive properties refer to the ability of a substance, mixture, or article to rapidly release energy and gas, creating a pressure wave and potentially causing damage to the surroundings. In the context of a Safety Data Sheet (SDS), explosive properties are critical safety characteristics that indicate the potential for sudden, violent reactions under specific conditions.

An explosion involves:

Rapid chemical reaction: A fast exothermic reaction that produces large volumes of gas
Pressure generation: Sudden formation of high-pressure gases
Shock wave: Propagation of a pressure wave through the surrounding medium
Energy release: Rapid release of thermal and kinetic energy

Explosive properties can be intrinsic to a substance's molecular structure (e.g., presence of certain functional groups) or can arise from specific conditions (e.g., confinement of flammable vapors).

Key concepts related to explosive properties include:

Detonation: Supersonic combustion wave propagation (faster than the speed of sound in the material)
Deflagration: Subsonic combustion wave propagation
Sensitivity: Ease of initiation of an explosive reaction by heat, shock, friction, or other stimuli
Brisance: Shattering effect or destructive capability of an explosive
TNT equivalence: Comparison of explosive energy to that of trinitrotoluene (TNT)

Importance in Safety Data Sheets

Information about explosive properties in an SDS is critical for several reasons:

Hazard classification: Determines classification under GHS and other regulatory systems
Risk assessment: Enables evaluation of explosion risks in workplaces and processes
Storage requirements: Informs appropriate storage conditions, including temperature controls, confinement, and segregation from incompatible materials
Handling procedures: Guides safe handling practices, including controls for ignition sources, impact, and friction
Emergency response: Provides critical information for emergency planning and response
Transportation regulations: Determines transportation hazard classes and packaging requirements
Process safety: Essential for designing safe processes and equipment

Types of Explosive Hazards

Several types of explosive hazards may be relevant in an SDS:

Type	Description	Examples
Intrinsically Explosive Substances	Substances with molecular structures that contain both oxidizing and fuel components, often with weak bonds	Nitroglycerin, TNT, organic peroxides, azides
Explosive Mixtures	Combinations of oxidizers and fuels that can explode when initiated	Ammonium nitrate/fuel oil (ANFO), black powder
Dust Explosions	Rapid combustion of finely divided solid particles suspended in air	Coal dust, flour, metal powders, wood dust
Vapor Cloud Explosions	Explosion of flammable vapor mixed with air when ignited	Gasoline vapors, natural gas, solvent vapors
Pressure Vessel Explosions	Physical explosion due to overpressure in a confined space	Boilers, compressed gas cylinders, autoclaves
Reactive Chemical Explosions	Violent reactions between incompatible chemicals	Strong oxidizers with organic materials, water-reactive metals
Decomposition Explosions	Self-accelerating decomposition of unstable compounds	Certain peroxides, nitro compounds, acetylides

GHS Classification for Explosives

Under the Globally Harmonized System (GHS), explosives are classified into six divisions based on their behavior when initiated:

Division	Hazard Description	Examples
Division 1.1	Substances, mixtures, and articles that have a mass explosion hazard (affects almost the entire quantity instantly)	TNT, dynamite, nitroglycerin
Division 1.2	Substances, mixtures, and articles that have a projection hazard but not a mass explosion hazard	Certain ammunition, some fireworks
Division 1.3	Substances, mixtures, and articles that have a fire hazard and either a minor blast hazard or a minor projection hazard or both	Certain propellants, some fireworks
Division 1.4	Substances, mixtures, and articles that present no significant hazard; only a small hazard in the event of ignition	Consumer fireworks, small arms ammunition
Division 1.5	Very insensitive substances or mixtures that have a mass explosion hazard	Certain blasting agents, ANFO
Division 1.6	Extremely insensitive articles that do not have a mass explosion hazard	Certain specialized military explosives

Additionally, GHS includes classifications for:

Self-reactive substances and mixtures: Thermally unstable substances that can undergo strongly exothermic decomposition even without oxygen
Organic peroxides: Substances containing the -O-O- structure that can be considered derivatives of hydrogen peroxide

Testing Methods for Explosive Properties

Test Method	Description	Application
UN Test Series 1	Determines if a substance has explosive properties	Initial screening for explosive properties
UN Test Series 2	Determines if a substance is too insensitive for inclusion in the explosives class	Further assessment of substances with potential explosive properties
UN Test Series 3	Determines sensitivity to thermal and mechanical stimuli	Thermal stability and sensitivity to impact and friction
BAM Fallhammer Test	Measures sensitivity to impact	Determination of impact sensitivity
BAM Friction Apparatus	Measures sensitivity to friction	Determination of friction sensitivity
Koenen Test	Measures response to intense heat under confinement	Assessment of thermal sensitivity under confinement
DSC/DTA	Differential Scanning Calorimetry/Differential Thermal Analysis to measure heat flow during decomposition	Thermal stability assessment
20L Sphere Test	Measures dust explosion parameters	Assessment of dust explosion hazards

Explosive Properties Parameters

Parameter	Description	Significance
Impact Sensitivity	Minimum energy required to cause initiation by impact	Indicates sensitivity to mechanical shock
Friction Sensitivity	Minimum force required to cause initiation by friction	Indicates sensitivity to frictional forces
Thermal Sensitivity	Temperature at which rapid decomposition or explosion occurs	Important for storage and process safety
Detonation Velocity	Speed at which the detonation wave propagates	Indicates explosive power and performance
Explosive Power	Energy released per unit mass	Indicates destructive potential
Critical Diameter	Minimum diameter for sustained detonation	Important for assessing risk in different geometries
Kst Value	Dust explosion severity index	Indicates relative explosion severity of combustible dusts
Minimum Ignition Energy (MIE)	Minimum energy required to ignite a dust cloud or vapor	Important for electrostatic hazard assessment

Structural Features Associated with Explosive Properties

Certain molecular structural features are associated with explosive properties:

Nitro groups (-NO₂): Present in many explosives (TNT, PETN, RDX)
Peroxide groups (-O-O-): Weak oxygen-oxygen bonds (TATP, MEKP)
Azide groups (-N₃): High-energy nitrogen-rich compounds (lead azide)
Acetylide groups (-C≡C-): Especially metal acetylides (copper acetylide)
Fulminates (-CNO): Highly sensitive compounds (mercury fulminate)
Diazo compounds (-N=N-): Nitrogen-rich compounds with weak bonds
High nitrogen content: Compounds with high N:C ratio often have high energy content
Strained ring systems: Compounds with strained molecular geometries

The presence of these structural features should trigger careful assessment of potential explosive properties.

Examples of Explosive Properties Descriptions in SDSs

"Explosive; mass explosion hazard (Division 1.1)"
"Not explosive based on molecular structure and oxygen balance"
"May form explosive peroxides upon prolonged storage in air"
"May form explosive dust-air mixtures if dispersed"
"Heating may cause an explosion (Self-reactive Type B)"
"Not explosive. Impact sensitivity: >40 J. Friction sensitivity: >360 N"
"May explode if heated under confinement"
"Explosive when dry. Keep wetted with 30% water by mass"

Regulatory Requirements

According to GHS and various regional regulations (EU CLP, US OSHA HazCom, etc.), information about explosive properties 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 specific physical and chemical properties related to explosivity.

For transportation purposes, explosive classification determines the appropriate UN hazard class, division, compatibility group, and shipping requirements under regulations such as ADR, IMDG, and IATA.

In many jurisdictions, the manufacture, storage, and use of explosives are subject to additional regulatory requirements and licensing.

Best Practices

When reporting explosive properties in an SDS:

Clearly state whether the substance or mixture has explosive properties
If explosive, provide the appropriate GHS classification and division
Include relevant test data (impact sensitivity, friction sensitivity, thermal stability)
Specify test methods used for determining explosive properties
Identify conditions that may lead to explosive behavior (heating, confinement, drying)
Provide information on sensitizing contaminants or conditions
Include appropriate warnings for substances that can form explosive peroxides or other hazardous derivatives
For dust-forming materials, include information on dust explosion hazards even if the bulk material is not classified as explosive
Ensure consistency between explosive properties information in different sections of the SDS
Provide clear guidance on safe handling, storage, and emergency procedures