ISO 2859-1 isn't just about sample sizes — it also defines three inspection severities: Normal, Tightened, and Reduced. Understanding when to switch between these levels is essential for effective supplier management.
Normal Inspection: The Starting Point
All new supplier relationships begin at Normal inspection. This is the standard General Level II sampling we discussed in our AQL guide. Normal inspection continues until there's statistical evidence that quality has shifted — either improved significantly or deteriorated.
Tightened Inspection: When Quality Slips
You switch to Tightened inspection when 2 out of 5 consecutive lots are rejected. At Tightened, sample sizes increase by approximately 40%, making it harder for marginal lots to pass. This puts pressure on the supplier to improve.
Tightened inspection continues until 5 consecutive lots are accepted, at which point you return to Normal. If quality remains poor under Tightened inspection for 10 consecutive lots, ISO 2859-1 recommends stopping inspection entirely — a strong signal that the supplier needs fundamental improvement before continuing the relationship.
Reduced Inspection: Rewarding Consistency
Reduced inspection is the reward for consistently good quality. You can switch to Reduced when 10 consecutive lots are accepted at Normal inspection, and the total number of defects in those 10 lots is within specific limits. At Reduced, sample sizes decrease by about 40%, saving inspection costs.
Practical Implementation
Most importers don't actively switch severities — they maintain Normal inspection for simplicity. However, for high-volume relationships, implementing switching rules can save 15-20% on inspection costs while maintaining quality pressure on underperforming suppliers.