Chemically active substances analysis evaluates the oxidizing, corrosive, flammable, pyrophoric, water-reactive, and self-decomposing properties of chemical materials to support safe handling, storage, transport classification, and regulatory compliance. Accredited third-party laboratories apply internationally recognized test methods from ISO, IEC, ASTM, GB, and the UN Manual of Tests and Criteria to generate reliable hazard data for GHS classification, safety data sheet preparation, and process safety management. This article explains the technical scope of chemically active substances analysis, typical sample types, key testing items, standard testing methods, industrial applications, and frequently asked questions.
Technical Overview
Chemically active substances are materials that readily undergo, initiate, or accelerate chemical reactions under normal or reasonably foreseeable conditions of use. The category includes oxidizing solids and liquids, organic peroxides, self-reactive substances, pyrophoric materials, substances that emit flammable gases on contact with water, corrosive acids and bases, polymerizable monomers, and combustible dusts. Because these materials can release heat, pressure, or aggressive reaction products, they are among the leading contributors to industrial fires, explosions, thermal runaway events, and corrosion damage.
Chemically active substances analysis combines physicochemical hazard testing with quantitative chemical measurement. Its objectives are to determine how reactive a material is, under which thermal or environmental conditions it becomes unstable, how it interacts with air, water, metals, and incompatible chemicals, and how much reactive content it actually contains. The resulting data underpin hazard classification under the UN Globally Harmonized System (GHS), dangerous goods classification under the UN Recommendations on the Transport of Dangerous Goods, chemical hazard communication requirements such as the GB 30000 series, and registration or notification schemes for new chemical substances.
For manufacturers, formulators, and downstream users, this analysis is not merely a compliance exercise. It provides the technical basis for storage temperature limits, incompatibility segregation, packaging selection, dust explosion protection, reaction hazard evaluation, and emergency response planning.
Testing Samples
Oxidizing Substances
Solid and liquid oxidizers such as nitrates, chlorates, perchlorates, permanganates, peroxides, hypochlorites, and persulfates, supplied either as pure technical products or as aqueous solutions and formulated mixtures. These samples are tested to determine whether they intensify combustion when mixed with combustible materials.
Organic Peroxides and Self-Reactive Substances
Dialkyl peroxides, peroxyesters, peroxydicarbonates, ketone peroxides, azo compounds, and thermally unstable intermediates. These samples require determination of active oxygen content, thermal stability, and self-accelerating decomposition behavior to define safe storage and transport conditions.
Flammable Liquids and Solids
Solvents, paints, coatings, adhesives, inks, aerosol products, matches, sulfur, and firelighters. Testing establishes flash point, ignition ease, and burning behavior for classification as flammable gases, liquids, or solids.
Pyrophoric and Water-Reactive Substances
Alkali metals, metal hydrides, organometallic catalysts, activated carbons, freshly divided metal powders, and water-treatment chemicals. These samples are evaluated for spontaneous ignition in air and for the rate and volume of flammable gas evolved on contact with water or humid air.
Corrosive Substances
Strong mineral acids, concentrated alkalis, acidic and alkaline salts, etching solutions, and cleaning formulations. Testing measures pH, titratable acidity or alkalinity, and corrosion rate against steel and aluminum reference metals.
Polymerizable Monomers and Process Chemicals
Styrene, acrylate and methacrylate monomers, vinyl acetate, isocyanates, epoxy resins, and curing agents. Analysis verifies inhibitor content, peroxide buildup, and exothermic polymerization potential over the product life cycle.
Combustible Dusts and Powders
Organic dusts from food, feed, wood, plastics, pharmaceuticals, and dyes, together with metallic dusts such as aluminum, magnesium, and iron powders. These samples are characterized for dust cloud and dust layer ignition sensitivity and explosion severity.
Testing Items
Depending on the material and its intended classification, the typical scope of chemically active substances analysis includes:
- Flash point, closed cup and open cup
- Auto-ignition and self-ignition temperature
- Oxidizing properties of solids and liquids, including burning time and pressure-rise comparison against reference oxidizers
- Thermal stability: decomposition onset temperature, heat of decomposition, and adiabatic behavior
- Self-accelerating decomposition temperature (SADT)
- Pyrophoricity of liquids and solids
- Gas evolution rate and total gas volume for substances emitting flammable gas in contact with water
- Flammability of solids: ease of ignition, burning rate, and flame propagation
- Corrosion rate to steel and aluminum for Class 8 assessment, together with pH and titratable acidity or alkalinity
- Active oxygen content and peroxide concentration in organic peroxides and peroxide-forming solvents
- Dust explosion parameters: explosion severity (Kst, Pmax), minimum ignition energy (MIE), minimum ignition temperature (MIT) of cloud and layer, minimum explosible concentration (MEC), and limiting oxygen concentration (LOC)
- Incompatibility and contact reactivity screening with water, acids, alkalis, oxidizers, and common packaging materials
- Identification of evolved or decomposition gases by gas chromatography and mass spectrometry
Testing Methods
Thermal Analysis
Differential scanning calorimetry (DSC) performed in accordance with ASTM E537 and ISO 11357 determines decomposition onset temperatures and heats of reaction. Thermogravimetric analysis (TGA) characterizes mass loss and multi-stage decomposition. Accelerating rate calorimetry (ARC) per ASTM E1981 provides adiabatic self-heating data and time-to-maximum-rate curves, while kinetic evaluation per ASTM E698 supports SADT determination and shelf-life estimation for self-reactive substances and organic peroxides.
Ignition and Flash Point Testing
Flash point is measured using the Pensky-Martens closed cup method per ISO 2719, ASTM D93, GB/T 261, and JIS K 2265, the Tag closed cup method per ASTM D56, the equilibrium closed cup method per ISO 3679, and the Cleveland open cup method per ISO 2592, ASTM D92, and GB/T 3536. Auto-ignition temperature of liquids is determined per ASTM E659, and ignition sensitivity of dust clouds and layers per ASTM E1491 and ASTM E2021.
Oxidizing Properties Testing
Oxidizing potential is assessed using the United Nations Manual of Tests and Criteria test protocols, in which the sample is mixed with a combustible reference substance such as cellulose and its burning time or pressure rise is compared with standardized reference oxidizer mixtures. Screening-level assessments using DSC and heat-of-mixing calorimetry help define the required test program before formal classification tests are performed.
Reactivity with Water and Pyrophoricity Testing
Standardized gas evolution tests measure the rate and total volume of flammable gas released when the sample contacts water, which determines classification for substances that emit flammable gases in contact with water. Pyrophoric testing observes whether liquids or powders ignite spontaneously within a defined exposure period when dropped or poured in air.
Corrosivity Testing
Corrosion rate testing exposes steel and aluminum coupons to the liquid sample under controlled temperature and time conditions to assess metal-destroying capability for transport Class 8 classification. Complementary pH measurement and titratable acidity or alkalinity determination characterize skin and eye corrosion potential for mixture classification purposes.
Dust Explosion Testing
Explosion severity indices (Kst and Pmax) are measured in a 20-liter sphere or larger vessel per ASTM E1226 and ISO 6184-1. Minimum ignition energy is determined per ASTM E2019, minimum explosible concentration per ASTM E1515, and electrostatic ignition hazards are assessed with reference to the IEC 60079-32 framework. These data drive area classification, explosion venting and suppression design, and inerting requirements.
Quantitative Chemical Analysis
Active oxygen in organic peroxides is determined by iodometric titration, oxidizer content by redox titration, and inhibitor levels by chromatographic methods. Ion chromatography, elemental analysis, Karl Fischer moisture determination, and gas chromatography with mass spectrometric detection are used to quantify reactive components and identify decomposition or reaction gases.
Applications
Chemically active substances analysis serves a wide range of industrial and regulatory purposes:
- Dangerous goods classification and packaging selection for road, sea, and air transport under the UN transport regulations
- GHS classification, hazard labeling, and safety data sheet authorization for acids, oxidizers, peroxides, flammable products, and reactive mixtures
- Process safety management, including safe storage temperature definition, incompatibility segregation, thermal runaway prevention, and emergency relief system design support
- New chemical substance notification and chemical registration dossiers requiring physicochemical hazard endpoints
- Battery and energy storage material evaluation, including reactivity screening of electrodes, electrolytes, and cell-level thermal runaway testing referenced in UL 9540A
- Quality control and shelf-life management of organic peroxides, polymerizable monomers, and inhibitor-containing products
- Combustible dust hazard assessments for food, feed, woodworking, plastics, metal processing, and pharmaceutical manufacturing plants
- Incident investigation and failure analysis following fires, explosions, or unexpected exothermic events
FAQ
What are chemically active substances?
They are materials with an inherent tendency to undergo or promote chemical reactions, including oxidizers, organic peroxides, self-reactive and pyrophoric substances, water-reactive materials, corrosives, polymerizable monomers, and combustible dusts. Their reactivity can produce heat, pressure, flame, toxic gases, or corrosive attack, which is why systematic analysis is required before handling, storage, or transport.
Why is SADT important, and how does it differ from the decomposition onset temperature?
The self-accelerating decomposition temperature is the lowest temperature at which self-accelerating decomposition occurs within a specific commercial package, whereas the decomposition onset temperature from DSC is an intrinsic property measured on a small open or sealed sample. SADT determines the actual control and emergency temperatures for storage and transport and is the parameter used for classification of self-reactive substances and organic peroxides.
How much sample is required for testing?
Requirements vary by test. Screening thermal analysis typically needs only a few grams, flash point tests require several tens of milliliters, oxidizer classification and gas evolution tests require several hundred grams, and dust explosion programs may require one to several kilograms of representative powder. Accredited third-party laboratories usually provide a sample checklist after reviewing the safety information of the material.
How long does chemically active substances analysis take?
Individual flash point, pH, or DSC measurements can often be completed within a few working days, while full classification programs combining thermal stability, oxidizing properties, SADT, and gas evolution testing may require two to six weeks. Testing of unknown or highly energetic materials includes an additional safety screening phase before any large-scale tests are authorized.
Which standards govern the classification of chemically active substances?
Classification criteria are defined in the UN Globally Harmonized System and the UN Manual of Tests and Criteria, with national implementations such as the GB 30000 series in China. The underlying measurement methods are published by standards organizations including ISO, IEC, ASTM, and their regional and national counterparts such as EN and JIS standards.
Can the test program be customized for a specific process or customer requirement?
Yes. Accredited third-party laboratories routinely design tailored programs that combine standard classification tests with incompatibility studies, reaction screening, and thermal stability assessments under process-relevant conditions, ensuring that the data directly support process safety decisions rather than generic documentation alone.