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


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Flow chart of IFA's proficiency testing
Source: IFA


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). Nevertheless 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 [3]. 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 [4, 5].

Organisation/carrying out of the proficiency testing schemes

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

When the samples are delivered, the processing period is stated, which is usually about four weeks. After the analysis and evaluation, the results are entered directly by the participants in the online portal. The input mask there contains all the necessary information for the data entry.

In addition, questions about the general conditions of sampling, if applicable, and the analysis and evaluation should be answered. Nevertheless answering the questions is voluntary. The participants receive an overview with the anonymised answers of all participants in the proficiency testing evaluation.


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 [6] (see Information for participants (PDF, 1.6 MB)). 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.

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 report 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

Certificate of attendance

Participants receive together with the PT report a certificate of attendance, see specimen (PDF, 52 kB).


[1] Gesetz über die Durchführung von Maßnahmen des Arbeitsschutzes zur Verbesserung der Sicherheit und des Gesundheitsschutzes der Beschäftigten bei der Arbeit (Arbeitsschutzgesetz – ArbSchG) vom 7. August 1996 (BGBl. I, S. 1246). Zuletzt geändert am 5. Februar 2009 (BGBl. I, S. 160)

[2] TRGS 402: Ermitteln und Beurteilen der Gefährdungen bei Tätigkeiten mit Gefahrstoffen: Inhalative Exposition (02.2010)

[3] Qualitätssicherung durch Ringversuche an der dynamischen Prüfgasstrecke des IFA (Kennzahl 1630) In: IFA-Arbeitsmappe Messung von Gefahrstoffen.

[4] DIN ISO 13528: Statistische Verfahren für Eignungsprüfungen durch Ringversuche (01.09). Beuth, Berlin 2009

[5] DIN EN ISO/IEC 17043: Konformitätsbewertung – Allgemeine Anforderungen an Eignungsprüfungen (ISO/IEC 17043:2010). Beuth, Berlin 2010

[6] DIN ISO 5725-2: Genauigkeit (Richtigkeit und Präzision) von Messverfahren und Messergebnissen – Teil 2: Grundlegende Methode für Ermittlung der Wiederhol- und Vergleichpräzision eines vereinheitlichten Messverfahrens (12.02). Beuth, Berlin 2002