SECTION 10.3: Possibility of Hazardous Reactions

Overview

This subsection identifies potential chemical reactions that could create hazardous situations during storage, handling, or foreseeable misuse. The analysis aligns with CLP Regulation Annex I requirements and ECHA guidance on reactive hazards.

Key Reaction Types

Reaction Type Trigger Conditions Potential Hazards Example Substances
Decomposition Heat >150°C, shock, contaminants Release of toxic gases (CO, HCN), explosive byproducts Organic peroxides, azides
Polymerization Temperature >80°C, inhibitor depletion Exothermic runaway reactions, vessel rupture Styrene, acrylic monomers
Oxidation-Reduction Contact with incompatible materials Fire/explosion, toxic gas generation KMnO₄ + glycerol, Na + H₂O
Hydrolysis Moisture exposure Violent gas release, heat generation AlCl₃, PCl₅
Isomerization UV exposure, catalytic surfaces Uncontrolled energy release Nitro compounds

Reaction Risk Assessment Matrix

Likelihood Severity Risk Level Mitigation Required
Probable Catastrophic Critical Engineering controls + PPE
Possible Major High Procedural controls + monitoring
Rare Moderate Medium Warning labels + training

Critical Reaction Parameters

  • Self-Accelerating Decomposition Temperature (SADT): Minimum temp causing exothermic decomposition within 7 days (UN Test H.1-H.4)
  • Adiabatic Temp Rise: ΔT >200°C indicates high reaction hazard potential
  • Gas Evolution Rate: >1 mL/g·min requires pressure relief systems

Hazardous Reaction Testing Methods

  1. Accelerating Rate Calorimetry (ARC): Measures self-heating rates under adiabatic conditions (ASTM E1981)
  2. Differential Scanning Calorimetry (DSC): Identifies exothermic peaks using heating rates 2-10°C/min (OECD TG 113)
  3. Reactive System Screening Tool (RSST): Assesses runaway reaction potential in closed systems
  4. 24-Hour Thermal Stability Test: Exposure at 75°C with pressure monitoring (UN Test N.1)

Example: Hydrogen Peroxide Decomposition

2H₂O₂ → 2H₂O + O₂↑ (ΔH = −98.2 kJ/mol)

Hazard Profile:

  • SADT: 85°C (unstabilized)
  • Catalytic contaminants: Fe³⁺, Cu²⁺, organic materials
  • Pressure build-up rate: 10 bar/min at 100°C

Preventive Measures

  • Maintain inhibitor concentrations >0.1%
  • Use chemically compatible materials (316L SS, PTFE)
  • Implement max shelf-life limits (e.g., 6 months for peroxide-formers)
  • Conduct quarterly stability checks for sensitive materials

Emergency Response Preparedness

  • Venting capacity: 1 m³ gas/kg substance
  • Neutralization protocols (e.g., 10% NaHCO₃ solution for acid spills)
  • Thermal runaway shutdown procedures (quench systems)