The rule
Even where no single substance exceeds its threshold, several dangerous substances held together can create an equivalent hazard. The summation rule measures that:
- For each substance, take quantity ÷ that substance's threshold.
- Add the ratios within the same hazard heading.
- If a total is one or greater, the establishment is in scope at that tier.
Three separate totals
| Heading | What it covers |
|---|---|
| Health hazards | Acute toxicity and related health classes |
| Physical hazards | Explosive, flammable, oxidising and related classes |
| Environmental hazards | Classes hazardous to the aquatic environment |
The three totals are never mixed; each is calculated separately, and any one of them passing 1 brings the establishment into scope.
Lower and upper tier are calculated separately
The same arithmetic is done once with lower-tier thresholds and once with upper-tier thresholds. An establishment can be in scope at the lower tier and not at the upper; its obligations follow accordingly.
Why most errors happen here
Someone reading the inventory sees that no line exceeds a threshold and concludes “we are out of scope”. But if ten substances each stand at a fifth of their threshold, the total is two and the establishment is in scope. Done by hand, this calculation also goes stale, because it is not redone when a classification changes or a new substance arrives.
How this stands in Optifora
The threshold list is held as 69 rows, and the summation is computed under three headings and for both tiers; a change in the inventory refreshes it automatically.