ISO 2859-5:2005 PDF

Overview

ISO 2859-5:2005 specifies a system of sequential sampling plans indexed by Acceptance Quality Limit (AQL) for lot‑by‑lot inspection by attributes. It supplements ISO 2859-1 by providing sequential schemes that achieve the same operating characteristics as single‑sample AQL plans but with substantially smaller average sample numbers. The standard is aimed at continuing series of lots where switching rules between normal, tightened and reduced inspection can be applied to protect the consumer and incentivize suppliers.

Keywords: ISO 2859-5, sequential sampling plans, AQL, sampling procedures, inspection by attributes, lot-by-lot inspection.

Key topics

• Sequential sampling schemes indexed by AQL: Statistical plans that decide lot acceptability by accumulating results over time rather than a single fixed sample.
• Reduction in average sample number: Sequential plans typically require far fewer inspections on average (documented potential savings up to ~85% vs single sampling for very good quality).
• Curtailment rule: A built‑in upper limit on sample size to control excessive inspection; the standard incorporates curtailment (upper limit typically expressed relative to the equivalent single sample size, e.g., 1.5 · n0).
• Switching rules: Procedures to move between normal, tightened and reduced inspection depending on the historical series of lot results, providing:
  • Enhanced consumer protection when quality deteriorates (tightened or suspended inspection)
  • Cost incentives when quality is consistently good (reduced inspection)
• Practical constraints and cautions:
  • Sequential plans are more complex and may be harder for inspectors to apply correctly.
  • Variable inspection time, sampling logistics and lot heterogeneity can reduce practical benefits.
  • Not suitable for isolated or very short lot series - ISO 2859-2 is recommended in those cases.

Applications

ISO 2859-5:2005 applies to attribute inspection across many contexts, including:

• End items, components and raw materials
• Materials in process and production operations
• Supplies in storage and maintenance operations
• Data, records and administrative procedures

Typical users:

• Quality managers and inspectors in manufacturing and supply chain operations
• Procurement and supplier quality engineers seeking lot‑level AQL control
• Third‑party auditors and regulatory bodies that require statistically based sampling
• Organizations where individual item inspection is costly relative to overheads

Related standards

• ISO 2859-1 - Sampling schemes indexed by AQL (single‑sample basis)
• ISO 2859-2 - Sampling plans for isolated lots (use when sequential schemes are not appropriate)
• Other parts of ISO 2859 (Parts 1–4, 10) for overview, skip‑lot procedures and assessment of declared quality levels

ISO 2859-5 helps organizations implement efficient, statistically equivalent AQL sampling with lower average inspection effort while retaining consumer protection through switching and curtailment rules.