Information for proficiency testing participants for in-house and external measuring stations

Introduction

It is the duty of the company to determine whether a concentration of hazardous substances is in the air at the workplace. The required measurements of the hazardous substances can be conducted by in-house or external measuring stations. A measuring station can be considered to be suitable if it has the necessary expert knowledge and the required facilities. The qualification is assured via an accreditation for measuring stations outside the company [1].

No formal accreditation is provided for in-house measuring stations (IMS). Then the in-house measuring stations also have to fulfil the requirements for measuring stations according to TRGS 402 (Technical Regulation for Hazardous Substances) [2]. To maintain the quality parameters for analytic procedures, the quality assurance methods are to be used that are state-of-the-art. The Institute for Occupational Safety and Health of the German Social Accident Insurance (IFA) provides proficiency testing as support and assistance for the measuring stations. This should give them an opportunity to examine and document their own quality through external quality assurance procedures.

All proficiency testing schemes are being conducted in compliance with DIN ISO 13528 and with DIN ISO/IEC 17043 [3, 4].

Organisation of the proficiency testing

The production of the samples is done either at the IFA, or at the Institute for the Research of Hazardous Substances (IGF) of the German Social Accident Insurance Institution for the raw materials and chemical industry (BG RCI) in Dortmund.

Processing and documenting the analytic results

At the end of every year, the schedules for the respective PT scheme in the following year are announced. Once the samples are sent, the processing time is given - generally a period of around four weeks. This time frame may not be exceeded because results that arrive at IFA after the given deadline (date of postmark) are not considered in the evaluation.

The samples include a USB-stick (2.0) for data collection. The results are collected with a special data entry program. The program runs on all Windows versions above Windows 2000. A hardcopy printout of the results is to be produced, signed, and sent to the IFA together with the memorystick.

The complete statistical evaluation is carried out by the IFA. The data received are immediately made anonymous by the IFA. Then the analysis and a graphical presentation are prepared using the software Prolab Plus (of quo data, Dresden/Germany). The results will be evaluated using the z-score evaluation according to DIN ISO 5725-2 [5].Upon completion of the evaluation, each participating measuring station receives a confirmation of participation with the following data:

• Laboratory number
• Own laboratory result and |z|-score
• Mean value of the samples following elimination of outliers (Grubbs test)
• Standard deviation
• Reference value (mean value of the control samples for quality control)

as well as an PT protocol with the following information:

• Tabular and graphical presentation of the entire analysis results and the outliers
• Tabular and graphical presentation of the |z|-score analysis
• List of the analysis methods employed by the participants
• Alphabetical list of all participants
• and a certificate of attendance

Evaluation

• General statistical parameters
• Outlier test conforming to GRUBBS
• z-score evaluation according to DIN ISO 5725-2 [5] (see Information for participants (PDF, 884 kB))

A result of |z| ≤ 2 is considered satisfactory, meaning that the PT is considered "passed". If the z-score is above two, a test of the analytic method used is suggested.

Certificate of attendance

Participants receive a certificate, see specimen (PDF, 52 kB).