ISO 13849: Frequency and/or exposure to hazard - how to decide F1/F2?

In ISO 13849-1, you need to choose F2 - frequent exposure if any of the following is true:

• A person is exposed to the hazard more frequently than once every 15 minutes and/or
• The total exposure time exceeds 1/20 of the machine’s operating time. However, this is computed per-shift basis, so if the exposure is more than 24 minutes per shift with the machine running the entirety of the 8-hour shift, you need to choose F2, even if the hazard occurs only on one day per month.

In case you have no available data to calculate the criteria above, choose F2 based on a worst-case assumption.

This is listed as an example in ISO TR 14121-2:2012 and in ISO 13849-1:2023 Appendix A.

Otherwise, choose F1 - infrequent exposure.

Source: ISO 13849-1:2023 Appendix A section A.3.2 (Annex A is informative, not normative), also shown in Pilz Machinery Safety Academy, ISO 14121-2:2012 (but without the very impotant note about “per shift”), CEFS certification course (TÜV Nord approved)