SECTION 10.5: Hazardous Decomposition Products

Overview

This subsection identifies hazardous substances generated during decomposition processes under normal handling conditions or foreseeable emergencies.

Key Decomposition Scenarios

  • Thermal decomposition (e.g., combustion, pyrolysis)
  • Hydrolysis reactions with water/moisture
  • Oxidation-reduction reactions
  • Catalytic degradation (e.g., metal ion-induced breakdown)

Common Hazardous Decomposition Products

Decomposition Type Typical Products Hazard Class (CLP) Example Substance
Combustion CO, CO₂, NOₓ Acute Tox. 1-3, STOT Polyvinyl chloride
Hydrolysis HCl, H₂S Skin Corr. 1B, Acute Tox. 2 Aluminum phosphide
Photolysis Free radicals Carc. 1B, Mut. 2 Chlorinated solvents
Catalytic breakdown Benzene derivatives Carc. 1A, Flam. Liq. 2 Styrene-butadiene rubber

Testing and Analysis Methods

Thermogravimetric Analysis (TGA)

  • Identifies decomposition onset temperatures
  • Sample mass loss vs. temperature profile
  • 20°C/min heating rate → 5% mass loss at 250°C = decomposition threshold

Additional Analysis Methods

  • GC-MS Decomposition Studies: Detects volatile organic byproducts
  • Reaction Calorimetry: Measures heat flow during decomposition events

Example: PVC Thermal Decomposition

C₂H₃Cl(n) →200°C HCl + aromatic hydrocarbons

Decomposition Details:

  • Products: HCl gas (Skin Corr. 1B), benzene (Carc. 1A)
  • CLP Requirements: GHS08, GHS05 pictograms