Spotting a high-hazard process
A screening checklist for reactivity, fire & explosion, toxicity and special reactions, with an interactive version.
Educational overview. The principles here are general and simplified, and the figures and rules of thumb are typical values, not limits for your plant. Decisions need process-specific data, the applicable codes and standards, and a qualified assessment.
Why screen at all?
A development team cannot run every safety test on every step. A high-hazard screen sorts the steps that need a full thermal and process-safety assessment from the ones that need only a basic check. It should happen early, when the route is chosen, because that is when changing the chemistry is still cheap.
The checklist below groups the warning signs used by many pharma and fine-chemical companies into four categories. One “high” flag is enough to treat the step as a high-hazard process.
How to read the energy numbers
| Indicator | Low | Medium | High |
|---|---|---|---|
| Adiabatic temperature rise ΔTad | < 50 K, no pressure build-up | 50–200 K | > 200 K |
| Decomposition energy (DSC) | < 100 J/g | 100–300 J/g | 300–500 J/g high; > 500 J/g severe: check explosive properties |
| TMRad at the worst temperature | > 24 h | 8–24 h | < 8 h |
The first two measure severity (how bad), the third probability (how likely, how fast). Risk needs both. The Stoessel diagram in lesson 5 puts them together.
Distillation residues, mother liquors, waste streams and hold tanks are where unstable by-products concentrate. Many incidents happened not in the reaction but while stripping a solvent to dryness.
🧾 Interactive screening checklist
Tick everything that applies to your process. Nothing is stored or sent anywhere.
● = high-severity flag
Key takeaways
- Screen every step early; one high flag means a full assessment.
- Severity: ΔTad (50 / 200 K) and decomposition energy (100 / 300 / 500 J/g). Probability: TMRad (8 / 24 h).
- Residues, distillations to dryness and all-in heated batches are classic traps.