AQL is the statistical sampling system that turns “how many defects are acceptable” from a vague conversation into a specific number agreed in writing. Defined under ISO 2859-1, AQL specifies the sample size to inspect from a given batch size at a given inspection level, and the accept/reject threshold based on the number of defects found.
How AQL works in practice
A buyer and a factory agree on an AQL percentage. Common AQL values for industrial chemicals and materials:
| AQL | Severity | Typical use |
|---|---|---|
| 0.65 | Critical defects | Pharma-grade, food-contact, electronics-grade |
| 1.5 | Major defects (high spec) | Specialty chemicals, fine chemicals |
| 2.5 | Major defects (standard) | Bulk industrial chemicals |
| 4.0 | Minor defects | Packaging, labelling, non-functional |
| 6.5 | Cosmetic defects | Outer drum dents, label scuffs |
For a single shipment you might agree multiple AQL values, 0.65 for critical defects, 2.5 for major, 4.0 for minor, and the inspection report scores against all three.
Sample size determination
AQL sample size is set by the batch size and the inspection level. ISO 2859-1 publishes lookup tables. For a typical chemical batch of 100 to 200 drums, a Level II inspection draws roughly 32 samples. Increase to Level III for tighter scrutiny on critical batches; decrease to Level I for relaxed inspection on consistently-clean factories. The samples are inspected against the spec, defects are counted, and the count is compared against the AQL accept/reject threshold for that sample size.
What an AQL fail actually means
An AQL fail does not mean every drum is bad. It means the defect rate in the sample, projected to the full batch, exceeds the agreed acceptance threshold. The factory’s options after an AQL fail:
- 100% inspect and rework. Inspect every drum, segregate defective units, ship the cleaned batch. Slowest and most expensive option.
- Reproduce the batch. Rejected batch returns to production; new batch produced. Multi-week delay.
- Renegotiate spec. Sometimes the AQL was set too tight relative to factory capability and renegotiating to a more realistic AQL is the practical solution. Risky on first orders; reasonable on repeat orders where the factory’s normal capability is clear.
The buyer chooses, not the factory. The AQL agreement gives the buyer the option.
AQL for chemical products specifically
AQL is most often applied to products with discrete defective-or-not characteristics: drum integrity, label correctness, fill weight accuracy, batch traceability marking. For continuous-variable characteristics (purity assay, residual solvent content, moisture) the relevant standard is the COA spec table. AQL applies less cleanly because each unit is not pass/fail, it is a measured value.
A practical chemical inspection therefore combines:
- AQL inspection for packaging, labelling, sealing, drum condition
- COA verification with third-party lab testing for chemical specification
Both are necessary. AQL alone misses contaminated chemical inside clean drums; COA alone misses leaking drums of in-spec chemical.
Practical sourcing notes
For our chemical shipments, the agreed AQL is written into the purchase order before the factory begins production: AQL 0.65 critical, 2.5 major, 4.0 minor. The pre-shipment inspector applies these thresholds during the SGS or Bureau Veritas inspection. If the inspection fails any of the three thresholds, the cargo does not seal until the factory addresses the defects. The cost of catching defects before sailing is the inspection fee. The cost of catching them at the destination port is at least an order of magnitude higher.
Related terms
SGS and Bureau Veritas are the third-party inspection bodies that conduct AQL sampling at the factory. COA covers the continuous-variable spec checks that AQL does not. MSDS is unrelated to AQL but travels with the same shipment.