Quality standards. How to choose gloves? Recommendations for practitioners Acceptable level of quality aql
Practically at any industrial enterprise that mass-produces its products, the task of statistical acceptance control arises.
What is statistical acceptance control? To answer this question, we turn to the Great Soviet Encyclopedia. So:
Acceptance statistical control - 1) this is a set of statistical methods for controlling mass products in order to identify their compliance with specified requirements; 2) it is an effective means of ensuring the good quality of mass production.
This paper describes one of the varieties of statistical acceptance control - control by an alternative feature.
All procedures of this type of control are standardized and described in GOST R ISO 2859-1-2007 "Part 1: Sampling plans for successive lots based on an acceptable quality level" and GOST R 50779.72-99 "Part 2. Sampling plans for individual lots based on the quality limit LQ".
The purpose of these procedures is to influence the supplier economically and psychologically through the possible rejection of lots, as well as to help maintain an average level of process quality, while at the same time ensuring the risk limit of accepting low quality lots (customer risk) at the proper level.
In addition, these procedures provide
automatic protection of the consumer in cases of detection of quality degradation,
incentive to reduce control costs while achieving a stable level of quality.
This paper describes both the theoretical aspects of the procedures for acceptance control by an alternative sign, and the software package that implements these procedures based on a powerful statistical package. STATISTICS.
Task description
Within the framework of this work, the following task is considered:
A large set of objects of 2 types is considered. It's about the party N products in which n products turn out to be defective (that is, they have at least one defect), and the rest N - n are suitable.
With the unknown n one can estimate this number from a relatively small sample by choosing at random (randomly) m products and identifying all of them defective (let their number be equal to k).
Let's calculate the probability of the event , where is the random number of defective products in the sample.
The probability of this event is described by the hypergeometric distribution and is equal to
, where k= 0, 1, …,
Based on the observed number, it is possible to estimate the percentage of defects (input defectiveness level) in the entire batch with a volume of N.
From the point of view of statistics, during acceptance control, the hypothesis is tested H0: that the batch is good, against the alternative H1: that party is not good.
Here q0- the value of the percentage of rejects, when the lot is still considered good.
Usually, during sampling, batches are divided into good and bad using two numbers - AQL (acceptance level of defects) and LQ (rejection level of defects). Lots are considered good at and bad at q> LQ. With AQL< q < LQ (так называемая область неопределенности) качество партии считается ещё допустимым.
The acceptance level of defectiveness AQL is the maximum permissible value of the defectiveness level in a lot produced during the normal course of production. The defective quality level LQ is the limit for classifying products as defective.
According to GOST procedures, the so-called “sampling plans” are used for control on an alternative attribute.
The control plan establishes the number of units of production from each batch ( m) to be controlled and the required lot acceptance criteria.
Acceptance ( c) and, sometimes, rejection numbers. The lot is accepted if the number of defective items in the sample m < c .
A specific sampling plan is selected based on the following factors:
control level (normal, enhanced, weakened)
lot size
AQL level
Based on these factors, according to the GOST tables, a specific sampling plan is selected, i.e. sample size m and acceptance number c.
Each sampling plan is characterized by its operational characteristic (OC).
The operational characteristic of the control plan is the function P(q), equal to the probability of accepting a batch with a proportion of defective units of production q.
, where the probability of occurrence k defective units in a sample of m.
Most often, the operational characteristic is displayed in the form of a graph, where
, at q= AQL
, at q= LQ.
Here, is the supplier's risk, which is equal to the probability of rejecting a lot with q= AQL (error of the first kind of accepting the alternative " H1: Lot rejection" vs. hypothesis " H0: acceptance of the party"); - the risk of the consumer, equal to the probability of accepting a batch with q= LQ (error of the second kind).
By setting the risk levels and , based on a specific sampling plan, it is possible to calculate the corresponding AQL and LQ numbers, on the basis of which a decision is made to accept or reject the entire lot.
Calculator
The task described in the previous section was implemented as a statistical acceptance control (STC) probabilistic calculator.
In this version of the calculator, the calculation of the parameters of a single-stage sampling plan is implemented, according to GOST R ISO 2859-1-2007.
This application is written on the Visual Basic .NET platform using the statistical package libraries STATISTICS.
The calculator has an intuitive user interface and is easy to use.
The calculator interface is implemented in the form of two windows:
welcome window
main dialog box
After starting the calculator, the user sees a welcome window.
Rice. 1. Welcome window
While this window is displayed, the system is booting in the background STATISTICS.
After the system STATISTICS loaded, the welcome window disappears and the main calculator dialog box appears.
Rice. 2. Main dialog box
In the main window, you can set the following characteristics of the sampling plan:
After setting all the parameters of the plan, you must press the "Calculate" button.
Based on the first three characteristics entered, the calculator will calculate and plot the Operational Characteristics curve for this plan.
In addition, the calculator will mark the risk levels of the supplier and consumer on the OX curve and calculate the corresponding AQL and LQ numbers.
Rice. 3. OX curve
Example
As an example, consider the acceptance control of batches of bearings on an alternative basis.
Let the batch size of bearings be 150 pieces. According to the procedures of GOST R ISO 2859-1-2007, we must choose a sample size code. At the control level “general - II”, a batch size of 150 units corresponds to code F.
We consider a one-stage sampling plan. We are looking for the necessary plan in the GOST tables based on the sample size code F and the AQL level of 2.5%.
These parameters correspond to the following plan:
sample size N = 20
acceptance number c = 1
We launch the SPC calculator. We enter all the necessary parameters of the plan. The default supplier and consumer risk levels (according to GOST recommendations) are set to 5% and 10%, respectively.
Rice. 4. An example of using a calculator
After pressing the "Calculate" button, the calculator will display the OX curve and calculate the AQL and LQ numbers for the risk levels we have chosen.
In this example:
AQL = 1
LQ = 4
Those. to organize acceptance control of bearings with a lot size of 150 units using one-stage normal random control with supplier risk levels of 5% and consumer risk of 10%, it is necessary:
Case - production of fasteners
Let's consider an enterprise producing fasteners (various bolts, nuts, etc.) for the automotive industry.
Obviously, this type of product is characterized by increased requirements for its reliability and, consequently, acceptance control.
There are numerous specialized standards (both foreign DIN, ISO, and Russian GOST) that fully describe the requirements for parameters, tolerances, etc. fasteners.
Consider the production of fasteners in more detail.
The technological process for the production of bolts consists of the following main stages:
landing blanks;
transportation;
thread rolling.
When landing the workpiece, the locksmith controls all dimensions of the bolt:
bolt length (L);
smooth part diameter (d);
hex size (AV);
head height (k).
Rice. 5. Bolt parameters
When thread rolling:
thread outer diameter d outer = d;
average thread diameter d cf ;
thread length (b);
thread pitch.
According to the length of the thread, the bolts are divided into 3 types:
standard (standard thread length according to the bolt size group);
full (thread to the bolt head);
without carving.
Let us describe an example of the organization of acceptance control at a given enterprise.
Let's say this company has two bolt production lines. Each line, after appropriate adjustment by the fitter(s), is capable of producing finished bolts with specified parameters (for example, 20 pieces per minute).
Naturally, carrying out continuous control in this case is a very costly measure (the time and resources are huge). Therefore, one of the best options can be a single-stage selective control on an alternative basis.
This type of control is distinguished by its simplicity and cost-effectiveness in comparison with the complete control of products.
It is really very easy to organize a single-stage selective acceptance control.
Suppose we have assembled a batch of bolts of the same type, manufactured on the same line, established by a specific team of locksmiths, with a volume of 1000 pieces (approximately for one hour of line operation).
Next, you need to randomly select a certain number of bolts from this batch.
Further, these bolts are examined for compliance with their parameters (geometric dimensions) to the standards described in the GOST corresponding to this bolt. If any parameter of the controlled bolt does not meet the standard, then this bolt is considered defective.
Based on the number of defective bolts (or the number of defects), we can estimate the number of defective products in the entire batch.
However, we are faced with the following questions:
how many bolts to select for control,
What is the probability of erroneously rejecting a good batch, or vice versa, accepting a bad batch?
Naturally, the more bolts we extract from the batch for subsequent control, the less likely it is to make a mistake, but the greater the cost of organizing control.
To find the optimal sample size value, you can use the Statistical Acceptance Inspection (STC) calculator, developed on the platform of a powerful statistical package STATISTICS using GOST standards in the field of acceptance control.
The principle of operation of the SPC Calculator is described in detail in the first part of this material.
By setting the risk level of the supplier and consumer, the batch size, based on the standard level of nonconformities, using the SPC calculator, you can select the optimal sample size, acceptance and rejection numbers.
Let's consider a specific example.
Lot volume - 1000 pcs;
Normative level of inconsistencies NQL - 0.65%;
Supplier risk - 5%;
Consumer risk - 10%.
Based on the GOST tables, we are invited to use the following plan:
Sample size - 367 items;
Acceptance number - 1 pc.
Let's set the described parameters in the calculator, press the calculate button.
Rice. 6. Operational characteristics of the control plan for the production of bolts
Based on the results obtained, the acceptance number is taken equal to 1 piece, the rejection number is 4 pieces.
Those. if for a batch of 1000 bolts out of 367 randomly selected only one defective bolt was found, or there were none at all, then such a batch is recognized as suitable.
If in the same situation 4 or more defective bolts are found, then the batch is rejected (sent for complete control).
In other situations, the batch is subject to additional control (production of another sample or the use of multi-stage plans).
Having collected statistics on the number of good / bad batches for each production line, all teams of locksmiths and other production parameters, we can draw conclusions about the possible causes of defects in production.
This information will help the manager to outline an action plan to improve the situation with product quality, which in turn will allow:
increase the competitiveness of the product in the market;
reduce costs by switching to more economical control plans;
increase sales and, consequently, the income of the enterprise.
Bibliography
Rozanov Yu.A. Probability Theory, Stochastic Processes and Mathematical Statistics, Nauka, 1985.
Ivchenko G.I., Medvedev Yu.I. Mathematical Statistics, Higher School, 1992.
Borovikov V.P. Popular introduction to the program STATISTICS, Computer Press 1998.
Borovikov V.P., Borovikov I.P. STATISTICS. Statistical Analysis and Data Processing in the Windows Environment, Filin 1998.
Borovikov V.P. STATISTICS, The Art of Computer Data Analysis, Peter 2001.
Encyclopedia. Probability and mathematical statistics. (Chief editor Yu.V. Prokhorov), Moscow, Great Russian Encyclopedia, 1999.
GOST R ISO 2859-10-2008 “Statistical methods. Procedures for selective control on an alternative basis. Part 10. Introduction to the standards of the GOST R ISO 2859 series.
GOST R ISO 2859-1-2007 “Statistical methods. Procedures for selective control on an alternative basis. Part 1. Sampling plans for successive lots based on an acceptable level of quality.
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To the question How to calculate the AQL ("acceptable quality level" of a batch of goods)? given by the author Olga Aks the best answer is In any batch there are always products with defects. Even if the manufacturer independently checked each unit. As a rule, in relations with the manufacturer, the buyer does not expect absolutely perfect (in terms of quality) deliveries.
However, the buyer has the right to strive to minimize the number of defective products.
In order to answer the question of what this coefficient is, consulting companies have developed a special tool called AQL Tables (Acceptance Quality Limits - English quality limit).
AQL tables are a simple and powerful statistical tool that the auditor uses to determine:
1. How many product items need to be tested to get a statistically significant sample;
2. Where is the line between rejection and acceptance of a batch when it comes to products with defects. It's about on the calculation of the maximum permissible level of quality at which the evaluated batch of products can be accepted. The methodology is defined by the ISO 2859 standard.
For example, if the customer defines the acceptable number of products with a defect in the amount of 1.5% of the total number of products, this means that the AQL is 1.5%. Based on practice, all potential defects can be divided into three groups: critical, major and minor. For most consumer products, AQL takes the following values: 0% for critical defects - for example, if the product does not meet safety requirements; 2.5% for significant defects - a product that the end consumer is unlikely to buy; 4% for minor defects - there are slight deviations from the specification, but the end user most likely will not pay attention to them;
Limits vary by market and product type: AQL for electrical wires for aircraft will be much lower than those for electrical wires that will be used in the manufacture of phone chargers.
How to work with AQL tables AQL tables are written in the ISO 2859 standard and contain already calculated indicators for different product groups.
There are three parameters in the tables: volume, verification level and AQL. At the same time: Lot size is the number of units of one product. If you ordered the production of different products (table, chair and armchair) in a furniture factory, three separate quality control procedures must be carried out for each type of product.
The inspection level depends on... and affects the final number of units that will be inspected. AQL - calculated depending on the type of your product and market, that is, if you are positioned in the elite segment, you need to choose a lower AQL for major and minor defects.Medical gloves are one of the main means of ensuring infectious safety in a medical institution. Wide variety of medical gloves Russian market At present, as well as the aggressive marketing policy of a number of manufacturers, they do not always allow healthcare facility staff to adequately understand the types of gloves and choose the right products to ensure safe work with patients.
All properties (characteristics) of medical gloves can be divided into 3 main groups: the main ones are present in any glove, additional ones - specialized gloves may have, dubious ones - various marketing tricks of manufacturers and suppliers, designed, among other things, to reduce possible competition.
The main properties of a medical glove include:
1) material of manufacture.
The main manufacturing material is latex - an emulsion of rubber particles in an aqueous solution. There are natural or synthetic rubbers, depending on the type of rubber, natural latex is distinguished, as well as nitrile, polyisoprene, polychloroprene latex and vinyl (polyvinyl chloride, "plastic" latex).
Natural latex consists of more than 60% polyisoprene particles, which allows us to consider polyisoprene gloves as the closest in properties to conventional latex. The advantages of natural latex are widely known: gloves made of this material stretch well, fit the hand, are soft and elastic. At the same time, they contain a significant amount of proteins that cause allergic reactions and are not resistant to alcohols, oils, and esters. The world standard for the presence of proteins in a natural latex glove is less than 50 µg/g, determined by the Lowry method (colorimetric method). A number of manufacturers offer gloves with a protein level of less than 20 µg/g, and in early 2011, natural latex gloves completely free of proteins (MPXX technology - maximum protection) appeared.
Nitrile latex perfectly resists the action of alcohols, aldehydes, phenols and acids, which makes it possible to use nitrile gloves in laboratories, when working with aggressive environments, and when cleaning rooms in healthcare facilities. In addition, synthetic gloves are absolutely non-allergenic, as they do not contain proteins, but, nevertheless, very often cause contact dermatitis when long work. It is impossible to call nitrile gloves hypoallergenic. The disadvantages of nitrile gloves include low elasticity and extensibility, which prevents their widespread use in surgery.
Polychloroprene (neoprene) and polyisoprene gloves are quite expensive, so they are mainly used as surgical gloves. There is no justified need to use examination gloves made of neoprene and polychloroprene, since they are similar to nitrile in terms of resistance to chemicals. At the same time, the use of such gloves during surgical operations allows you to provide the highest level of protection for all members of the surgical team.
Vinyl gloves made from PVC - polyvinyl chloride, a short-lived and rather harmful substance. These gloves are cheap, but they have one important drawback: they are easily permeable to any proteins (including blood proteins) and microorganisms, which does not allow them to be used even for a short-term examination of patients.
Currently there are gloves having 2 different layers. for example, DermaGEL gloves from the Polish company Mercator Medical have an inner layer of nitrile or polyurethane, which gives the glove extra strength, insulates the skin from the action of natural latex proteins and greatly facilitates donning. The start of production of such hybrid gloves, combining the properties of different materials, is an important step towards creating a new level of infectious protection.
2) the presence or absence of powder
The negative properties of the powder used in the manufacture of gloves are widely known. Initially, the use of powder was due to the technological process of production, to prevent sticking of the walls after removal from the mold. In this case, multiple cleaning and rinsing steps were used to make powder-free gloves, resulting in a significant price difference between powdered and powder-free gloves. At present, such cleaning is used only by manufacturers with outdated equipment; at most enterprises, powder is excluded from the technological process, which has significantly reduced the difference in price. In order to keep the gloves from sticking together after demolding, most factories use surface modification - this process will be discussed later.
Powder is the strongest absorbent, attracting and holding proteins and microorganisms. Thus, it is a source of infectious danger, and enhances the allergic effect of natural latex on the skin. Numerous studies have shown a significant role of powder in the occurrence of postoperative complications, adhesions and scars, the occurrence of allergic reactions in both patients and healthcare facility staff, and the spread of nosocomial infections.
3) textured surface
The texture of the outer surface improves the grip of the medical instrument. During production, a textured surface is formed by using solutions of formers - chemicals that act on the outer surface of a glove that is not yet ready, not completely dry. In general, it is necessary to separate the concepts of a textured (textured) and micro-rough (micro rough) surface. In the second case, the surface of the glove changes very little and, in general, in terms of its contact properties, the microrough surface is closer to smooth than to textured. In addition, it is important to note that Russian GOSTs require the manufacturer to provide a minimum thickness of 0.08 mm for smooth sections of examination gloves, and 0.11 mm for textured ones. For surgical gloves, these values are 0.10 and 0.13 mm, respectively. Neither a smooth glove with a thickness of 0.07mm nor textured glove with a thickness of 0.10mm cannot be used for medical purposes.
4) presence / absence of a roller
The roller is a structural element of the glove, with the help of which the glove is fixed on the wrist. The main requirement for gloves with a roll is that the roll must be rolled up inside the glove, if it is rolled outward, the space between the roll and the outer surface of the glove is a source of significant infectious hazard. During a surgical operation, this space cannot be treated with a skin antiseptic and is a kind of storage for carrying bacteria. In the absence of a roller, a mandatory component of the glove should be a reinforced or reinforced cuff that fits snugly around the wrist. Gloves without a roll without a reinforced cuff are made from ordinary gloves by simply cutting off the roll, they do not fit and do not stick to the wrist and their use is not justified.
5) AQL
AQL (Eng. Acceptable Quality Level, Guaranteed Quality Level) - the maximum allowable number of defects in a batch of samples of a certain size. AQL is one of the most important quality indicators for mass production. In AQL testing - an acceptable quality level - a certain number of samples of manufactured products are selected according to a carefully defined procedure for random testing. These randomly selected samples are then tested in accordance with approved state standards and specifications. Based on the results obtained, a conclusion can be drawn about the quality of the entire batch of products. The higher the product quality requirements, the stricter the testing requirements.
Basically, they test medical gloves for water resistance. This is a procedure for determining the ability to retain water. 1000 ml is poured into the glove. water, while the glove should not leak for a certain period of time.
Thus, AQL is a statistical procedure for determining the quality of a glove.
The lowest AQL level allowed for a medical glove according to Russian GOST is 2.5, according to the European standard EN 455 - 1.5. There are medical gloves with an AQL of 1.0 or 0.65. clearly this indicator can be estimated as the probability of having defective items in a batch of 1000 boxes of gloves, 50 pairs each. With an AQL of 2.5, the probability that there will be no defective gloves in the box is only 3%, i.e. virtually every box in a batch will contain one, two, or more defective items. With AQL 1.5, the probability of having defective products in the box can be estimated at 22%, and with AQL 1.0 - at 6-8%.
Thus, a slight increase in the AQL level leads to a significant guaranteed reduction in the number of defective gloves in the lot.
6) Length and thickness
As mentioned above, Russian GOSTs (52238 - 2004 and 52239 - 2004) require the manufacturer to provide a minimum thickness of 0.08 mm for smooth sections of examination gloves, and 0.11 mm for textured ones. For surgical gloves, these values are 0.10 and 0.13 mm, respectively.
The length of an examination glove should not be less than 220mm, for a surgical glove - 255mm. Moreover, European standards EN 455 are even more stringent and do not allow lengths less than 240 and 280 mm for examination and surgical gloves, respectively.
At the same time, I would like to note that more and more diagnostic gloves are produced with a length of at least 290mm. Long gloves are absolutely essential when used as protective against harmful chemicals - in laboratories, when cleaning, when working with cytostatics or to protect against viral infections.
Additional properties of a medical glove include the following:
1) Anatomical shape.
GOST 52238 - 2004 indicates the presence of an anatomical shape as a prerequisite for classifying this glove as a surgical glove. In general, the shape of a glove with the thumb extended forward is called anatomical, which significantly reduces hand fatigue during work and long-term surgical operations. Anatomically shaped gloves are more expensive to manufacture than a regular (flat) shape and can only be worn on the corresponding - right or left - hand. For a more accurate selection of sizes for such gloves, digital (from 5.5 to 9) designations are used instead of the usual alphabetic ones for diagnostic gloves (XS, S, M, L, XL). Size XS corresponds to sizes 5.5 and 6, S - 6, 6.5 and 7, M - 7, 7.5 and 8, L - 8 and 8.5.
There is the concept of “improved anatomical shape”, which is a shape with fingers bent towards the palmar side, which reduces the load not only on the thumb, but also on all the others.
2) Sterility
The sterility of the glove is ensured by sterilization, i.e. complete release from all types of microorganisms, including bacteria and their spores, fungi, virions, as well as from prion proteins. Sterilization can be carried out by thermal, chemical, radiation, filtration methods; in industrial volumes, surgical gloves are sterilized by chemical (ethylene oxide gas sterilization) or radiation (gamma radiation) methods. Thermal sterilization of non-sterile gloves is carried out in the healthcare facility. Both radiation and gas sterilization are absolutely safe for the consumer and equally effective in removing microorganisms. Often the same manufacturer of gloves can be sterilized with both gamma radiation and ethylene oxide. As a rule, to confirm sterilization, an indicator is applied to the box, which changes its color with sufficient exposure intensity and confirms sterility.
3) Surface modification
Modification of the inner or outer surface of a medical glove is a common process designed to make the surface smoother. The modification of the inner surface is used to facilitate donning, including on wet hands, the modification of the outer surface is designed for more convenient work with small tools so that the contact surfaces of the fingers do not stick together.
There are 2 main methods of surface modification: chlorination (chlorination) and polymer treatment.
Chlorination- this is the treatment of a glove with perchloric acid, it can be single or double (on both sides). As a result of chlorination, latex particles are destroyed and form a smooth film on the surface. There is a process of partial dehydration, ie. removing water, making the glove feel drier to the touch. Chlorination can be carried out production line(online chlorination), and by soaking gloves in a perchloric acid solution for a long time. Online chlorination is one of the main ways to prevent gloves from sticking together after removal from the mold, this step has replaced technological process dusting. The concentration of chlorine in this case is extremely small and the process practically does not affect the properties of the glove. Double chlorination, carried out for a long time, significantly changes the properties of the glove. The destruction of the latex particles leads to a decrease in the elasticity and extensibility of the glove. Uncontrolled long-term chlorination leads to the appearance of an intense yellow color, makes the latex permeable to proteins and microorganisms, traces of chlorine on the surface of the glove can adversely affect both the doctor and the patient.
At the same time, an increase in the intensity of exposure has practically no effect on the properties of the surface - the surface becomes smooth even with not very strong chlorination.
Another method of surface modification is polymer treatment. The function of the polymer coating is to improve donning and prevent sticking of the glove. Almost any polymer can be used for surface treatment, polyurethane or silicone are most commonly used. When processing with polymers, it is not the formation of an additional functional layer, but a kind of smoothing of surface irregularities. The polymer-treated surface does not protect the skin from the action of latex proteins and does not interfere with the contact of natural latex with the skin, therefore it cannot serve as a protection against allergic reactions or contact dermatitis.
The questionable properties of medical gloves include the presence of a moisturizer (glycerin, tocopherol), extracts of aloe vera, chamomile, various compounds to improve skin trophism without confirming clinical efficacy and indicating the quantitative composition.
On packs of gloves, special markings are sometimes affixed. One of them is AQL. What is this indicator and what does it mean? Let's try to understand this issue. Acceptable Quality Level- This allowable level quality of medical gloves, or in other words, the percentage of acceptable marriage for the entire batch.
Naturally, production on conveyors has its own errors and it is too costly to control the quality level of each pair for 100%. Therefore, manufacturers have come up with such a method of selective testing, which allows you to highlight the component of defective products for the entire batch. If, as a result of testing, the value AQL exceeded the allowable rate, then the entire batch is recognized as unfit for use, and must be withdrawn from sale.
AT different countries AQL indicators for acceptable values are different. So, for example, RF, according to our requirements, viewing should have a value of no more than 2.5, and European standards require a stricter framework and correspond to a value of 1.5.
According to the AQL values, the following quality indicators are distinguished:
- 1 - very high
- 1.5 - high
- 2.5 - acceptable
- >3 - invalid
Accordingly, the lower the AQL, the higher the quality level of medical gloves.
Long-term practice shows that the majority of import manufacturers claiming AQL 1.5 do not correspond to the declared data and have a much higher defective rate. Therefore, the benefit that combines low price and low quality is highly questionable. A defective batch will eventually cost the same money, and the reputation of the supplier will be damaged and the medical staff will remain dissatisfied.
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What does ACL mean?
When using the services of an independent inspection company, it is very important to understand the standard used to take random samples for cosmetic inspection.
The most common standard for product inspection is ISO standard 2859-1 (ANSI/ASQC Z1.4-2003). It uses the AQL (Acceptable Quality Limit) concept.
What does ACL mean? The standard definition of AQL is “the maximum percentage of defects in a lot (or the maximum number of defects per hundred units of production) that can be considered as meeting average standards and acceptable for the purposes of lot acceptance for quality”.
Sample size, based on the AQL tables, will be selected and then checked for defects.
Defects are divided into three categories: minor, major and critical. Although different clients categorize differently, typical definitions are as follows:
- Minor defect- this is a non-compliance with standards, but something that most likely will not affect the use of the product.
- Major Defect is one that is most likely to result in the inability to use the product for its intended purpose.
- Critical Defect is one that is considered dangerous or unsafe.
According to the number of defects found and according to the number of defects allowed (figures are given in the AQL tables), your inspection company can advise you, accept or refuse from the party.
How to use AQL tables?
The AQL tables will help you determine the inspection sample size we need based on the quantity ordered and your inspection severity level. You can select Levels I, II, or III, with Level III being the most stringent and Level I being the least stringent. The standard level that is used by default and 98% of people is level II. The choice is up to the client, but this is the recommended level.
In order to find the required inspection sample size, you must first refer to the first table and on the left find the total number of products produced. For example, if you produce 8,000 pieces, at level II you see the letter L, which in the second table represents a sample size of 200.
At the top of the second table are defect levels from 0 to 6.5 (we cut out the higher numbers because they don't apply to consumer goods buyers).
You can choose which level to apply to your types of defects: critical, major, and minor. As a rule, most importers choose standard defect levels: 0/2.5/4.0 , but someone also chooses 0/1.5/2.5, this is at the request of the client.
Using standard defect levels of 0/2.5/4.0 and a sample size of 200, we can see that if you have more than 0 critical defects, 10 major defects, and 14 minor defects, you should discard that lot.
Of course, the decision what to do after receiving the results of the inspection, remains only with you. Most importers prefer to discuss what was found during the inspection with the supplier/manufacturer in order to improve anything that can be improved. In the event that the inspection results are very close to the AQL limits, it is important to double-check whether the level of defects found is acceptable to you or not.
