BS EN ISO 13855:2010 and BS EN 999:1998+A1:2008 compared

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Jon Severn, editor of, compares the newly published BS EN ISO 13855:2010, ' Safety of machinery - Positioning of safeguards with respect to the approach speeds of parts of the human body,' with the standard it replaces, BS EN 999:1998+A1:2008 (other EN versions of these standards will show the same differences).

BS EN ISO 13855:2010 Safety of machinery - Positioning of safeguards with respect to the approach speeds of parts of the human body was published on 31 May 2010 and replaces BS EN 999:1998+A1:2008 Safety of machinery - The positioning of protective equipment in respect of approach speeds of parts of the human body, which was withdrawn on the same day. The new standard is similar to the old one, but most of it has been rewritten and there are some important changes to be aware of. For example, as well as relating to safety light curtains and pressure-sensitive mats, the new standard is also applicable to certain physical interlocked guards.

If you design machines with safety light curtains or pressure-sensitive safety mats - or if you retrofit these to existing machines - then you will probably be familiar with BS EN 999. However, this standard is no longer current, so you now need to work to BS EN ISO 13855:2010. For machine builders based in Europe and exporting to other global markets, the new standard offers the advantage of being international. An important change in the standard that could impact on machine builders who do not use electro-sensitive protective equipment (typically light barriers) or pressure-sensitive protective equipment (typically mats but also 'safe edges') is that the standard now explicitly covers interlocking guards without guard locking. As with its predecessor, the new standard also covers two-hand control devices; although these are generally discouraged in the UK because they cannot prevent a second person from reaching into the hazardous area, they are still widely used in many markets.

Note that what follows is a comparison of BS EN ISO 13855:2010 and BS EN 999:198 +A1:2008. The differences will be the same between other national versions of these Euronorms, but the author has not compared ISO 13855:2010 with ISO 13855:2002. Note also that EN ISO 13855:2010 is not yet harmonised to the Machinery Directive 2006/42/EC, but this standard should be considered to represent the state of the art and working to it should give a presumption of conformity to the harmonised standard EN 999:1998+A1:2008. [See this article dated 1 June 2010 about Machinery Directive Harmonised Standards - new list - Ed]

1 Scope

This section has been largely redrafted, but points to note include the reference to 'parts of the human body' in place of 'hand/arm' and the safeguards considered in the standard now explicitly include 'two-dimensional vision systems' (but not three-dimensional vision systems) and 'interlocking guards without guard locking.'

2 Normative references

Not surprisingly, these have been completely updated to reflect recent changes in the standards. Note, however, that EN 574 ( Safety of machinery - Two-hand control devices - Functional aspects - Principles for design) is no longer referenced.

3 Terms, definitions, symbols and abbreviated terms

As tends to be the case with revised standards today, this section has been expanded considerably. For example, the following terms are all now defined: indirect approach; circumventing the detection zone; termination of the hazardous machine function; detection zone; minimum distance; and intrusion distance. In addition there is a new table that lists the symbols used in the equations presented in the standard, and a list of abbreviated terms.

4 Methodology

This has been revised so that it is now necessary to consider the possibility of the detection zone being circumvented, as well as safety distances calculated when using a combination of safeguards. The corresponding flow chart is very different indeed.

5 General equation for the calculation of the overall system stopping performance and minimum distances

This section now starts with an explanation of the way in which overall system stopping performance comprises 'at least two phases': reaction time of the protective device; and stopping time of the machine. In the old standard this material was included within Section 3 Definitions, though the new standard also includes additional information on this subject.

6 Calculation of minimum distances for electro-sensitive protective equipment employing active opto-electronic protective systems

This section has been largely redrafted, expanded and renumbered to improve clarity, and now includes specific references to vision-based protective devices (VPPD) and two-dimensional protective zones. Note that whereas EN 999 contained a table showing the number of light beams and the height above the reference plane (typically the floor), this information has now been moved to an informative Annex E. A small but significant addition (in 6.3) reads: 'Measures shall be applied so that the protective devices cannot be used to gain access to the hazard zone (eg by stepping or climbing on the housing).'

6.5 Addressing possible circumventing of electro-sensitive protective equipment by reaching over the detection zone is a completely new sub-section. It includes a table that looks similar to that in EN ISO 13857 Safety of machinery - Safety distances to prevent hazard zones being reached by upper and lower limbs but in fact is significantly different. Whereas the table in EN ISO 13857 gives safety distances, that in EN ISO 13855 gives distances that must be added to the product of the approach speed and the overall system stopping performance time. However, for much of the table this figure is given as zero, depending on the height of the hazard zone and the height of the upper edge of the detection zone.

6.6 Indirect approach - Path from detection zone to hazard zone restricted by obstacles is a new sub-section that is applicable when an obstacle is permanently fixed between the detection zone and the hazard zone. Because the person must reach around the obstacle, the approach speed differs from that for a direct approach. However, the standard states that obstacles should not be added to a machine with the sole purpose of reducing the approach speed.

Another point to note about section 6 is that the old 6.4 Dual position equipment has been deleted.

7 Method of calculating the positioning of pressure-sensitive mats or floors

This section has been slightly reworded for clarity, but it now includes a note relating to walking speeds and stride lengths; this information was previously contained in Annex B.

8 Two-hand control devices

This section is all but identical to that in the old standard.

9 Interlocking guards without guard interlocking

This new section relates to interlocked guards on machines that do not cease to be hazardous as soon as the guards are opened (eg machines with a rundown time). It is applicable to both manually operated and powered guards. Furthermore, the standard shows how to calculate the relevant distances taking account of the fact that (a) the guard takes time to open and (b) the body part that may project through the opening depends on how far the guard has opened.

Annex A, Worked examples

In many ways this is the same as the worked examples in the old standard, but with some exceptions. First, the example relating to dual position equipment has been deleted (in line with the deletion of the corresponding section in the body of the standard). Second, there are new examples that show how to use the tables for finding the additional distance to be used when reaching over the detection zone. Other examples have been added or rewritten for clarity.

Annex B, Termination of hazardous machine functions

This Annex explains what to consider when a hazardous machine function (such as motion) is altered in such a way that it is harmless for the human body. For example, a machine with a rundown time may decelerate to such a speed that the motion is no longer hazardous, even though it has not reached a complete halt. If the point at which the machine function becomes harmless cannot be determined, then the Annex says it is necessary to consider the time at which the machine comes to a complete halt.

Annex C, Example for considering indirect approaches

Because there is a new sub-section 6.6 that deals with indirect approaches, a worked example has been added. However, this has been allocated its own Annex rather than being included within Annex A.

Annex D, Measurement and calculation of overall system stopping performance

This new Annex is divided into four sections as follows:

  • D.1 When to give a stop signal
  • D.2 How to calculate the overall system stopping performance
  • D.3 Practices to be avoided
  • D.4 Good practice for making a protocol

Annex E, Number of beams and their height above the reference plane

As mentioned earlier, this new Annex contains the information previously included as Table 1 in sub-section 6.1.4.


There was no bibliography in BS EN 999 but, as tends to be the case with the current generation of international standards, BS EN ISO 13855:2010 includes a bibliography.


The above has been prepared to give an indication of the ways in which BS EN ISO 13855:2010 differs from BS EN 999:198 +A1:2008. While every effort has been made to ensure that the information is accurate, no responsibility can be accepted for any errors or omissions. Readers are responsible for ensuring compliance with all applicable regulations.

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