Acceptance sampling uses statistical sampling to determine whether to accept or reject a production lot of material. It has been a common quality control technique used in industry and particularly the military for contracts and procurement. A wide variety of acceptance sampling plans are available.
What is Acceptance Sampling?
- Contributions of Dodge and Romig to acceptance sampling - Acceptance sampling is an important field of statistical quality control that was popularized by Dodge and Romig and originally applied by the U.S. military to the testing of bullets during World War II. If every bullet was tested in advance, no bullets would be left to ship. If, on the other hand, none were tested, malfunctions might occur in the field of battle, with potentially disastrous results.
- Definition of Lot Acceptance Sampling - Dodge reasoned that a sample should be picked at random from the lot, and on the basis of information that was yielded by the sample, a decision should be made regarding the disposition of the lot. In general, the decision is either to accept or reject the lot. This process is called Lot Acceptance Sampling or just Acceptance Sampling.
- "Attributes" (i.e., defect counting) will be assumed - Acceptance sampling is "the middle of the road" approach between no inspection and 100% inspection. There are two major classifications of acceptance plans: by attributes ("go, no-go") and by variables. The attribute case is the most common for acceptance sampling, and will be assumed for the rest of this section.
- Important point - A point to remember is that the main purpose of acceptance sampling is to decide whether or not the lot is likely to be acceptable, not to estimate the quality of the lot.
- Scenarios leading to acceptance sampling - Acceptance sampling is employed when one or several of the following hold:
- Testing is destructive
- The cost of 100% inspection is very high
- 100% inspection takes too long
- Acceptance Quality Control and Acceptance Sampling - It was pointed out by Harold Dodge in 1969 that Acceptance Quality Control is not the same as Acceptance Sampling. The latter depends on specific sampling plans, which when implemented indicate the conditions for acceptance or rejection of the immediate lot that is being inspected. The former may be implemented in the form of an Acceptance Control Chart. The control limits for the Acceptance Control Chart are computed using the specification limits and the standard deviation of what is being monitored (see Ryan, 2000 for details).
- An observation by Harold Dodge In 1942, Dodge stated: "....basically the "acceptance quality control" system that was developed encompasses the concept of protecting the consumer from getting unacceptable defective product, and encouraging the producer in the use of process quality control by: varying the quantity and severity of acceptance inspections in direct relation to the importance of the characteristics inspected, and in the inverse relation to the goodness of the quality level as indication by those inspections." To reiterate the difference in these two approaches: acceptance sampling plans are one-shot deals, which essentially test short run effects. Quality control is of the long-run variety, and is part of a well-designed system for lot acceptance.
- An observation by Ed Schilling Schilling (1989) said: "An individual sampling plan has much the effect of a lone sniper, while the sampling plan scheme can provide a fusillade in the battle for quality improvement."
- Control of product quality using acceptance control charts - According to the ISO standard on acceptance control charts (ISO 7966, 1993), an acceptance control chart combines consideration of control implications with elements of acceptance sampling. It is an appropriate tool for helping to make decisions with respect to process acceptance. The difference between acceptance sampling approaches and acceptance control charts is the emphasis on process acceptability rather than on product disposition decisions.
Safety Management Systems
Safety Management System (SMS) is a term used to refer to a comprehensive business management system designed to manage occupational safety and health elements in the workplace. It is a systematic, explicit and comprehensive process for managing safety risks. As with all management systems, a safety management system provides for goal setting, planning, and measuring performance. A safety management system is woven into the fabric of an organization. It becomes part of the culture, the way people do their jobs.
There are three imperatives for adopting a safety management system for a business
These are ethical, legal and financial There is an implied moral obligation placed on an employer to ensure that work activities and the place of work to be safe, there are legislative requirements defined in just about every jurisdiction on how this is to be achieved and there is a substantial body of research which shows that effective safety management (which is the reduction of risk in the workplace) can reduce the financial exposure of an organisation by reducing direct and indirect costs associated with accident and incidents.
To address these three important elements, an effective SMS should:
- Define how the organisation is set up to manage risk.
- Identify workplace risk and implement suitable controls.
- Implement effective communications across all levels of the organisation.
- Implement a process to identify and correct non-conformities.
- Implement a continual improvement process
Basic Safety Management Components
Since there are many models to choose from to outline the basic components of a safety management system, the one chosen here is the international standard promoted by the International Labour Organisation (ILO). In the ILO document ILO-OSH 2001 Guidelines on Occupational Safety and Health Management Systems, the safety management basic components are:
- Policy
- Organizing
- Planning and Implementation
- Evaluation
- Action for Improvement
Although other SMS models use different terminology, the process and workflow for safety management systems is always the same;
- Policy - Establish within policy statements what the requirements are for the organisation in terms of resources, defining management commitment and defining OSH targets
- Organizing - How is the organisation structured, where responsibilities are and accountabilities defined, who reports to whom and who is responsible for what.
- Planning and Implementation - What legislation and standards apply to our organisation, what OSH objectives are defined and how are these reviews, hazard prevention and the assessment and management of risk.
- Evaluation - How is OSH performance measured and assessed, what are the processes for the reporting of accidents and incidents and for the investigation of accidents and what internal and external audit processes are in place to review the system.
- Action for Improvement - How are preventative and corrective actions managed and what processes are in place to ensure the continual improvement process?
Contents of a safety plan
Employers developing a Safety Plan need to consider their particular workplace and organizational needs to ensure the plans relevance. As a minimum, the Safety Plan should:
- include your OHS Policy signed by senior management;
- detail key staff and the organizational structure responsible for the management of safety;
- identify hazards associated with the work;
- explain methods of hazard identification including checklists and other methods to be used;
- detail risk assessment and control measures;
- list instruction and training and experience of the contractor’s employees;
- include the types of records that will be kept and who is to keep them;
- state the monitoring and safety requirements that will be used;
- identify safety meetings and the means of resolving safety issues;
- reference or include written work procedures, and
- include emergency procedures.
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