Machine safety: Reduced-energy operating modes

by Oct 24, 2018Machine Safety

Machine safety: Reduces-energy operating modes


Access to the danger zone of a machine during maintenance, or even setup and installation activities, should only be allowed once all energies have been controlledby use of lockout, according to article 188.2 of ROHS [1].


Access to the danger zone during operation

However, some activities not only require access to the danger zone, but also require operation of the equipment. This often translates into operation of the equipment with its protectors having been removed or displaced, or with its protective devices having been neutralized. Article 189.1 of ROHS provides for a specific control mode for these types of activities. This is what we call a reduced-energy operating mode.


What does this entail?

First, it is an overriding operating modethat, when selected, causes all other control modes of the machine to become inoperative. From this point on, the regulation allows for two possibilities:

  1. Either the control device used is of the hold-to-run controltype, in order to continuously maintain control of the machine’s motion;
  2. Either the machine is operated at reduced energy levels, (e.g. reduced speed, reduced force, step-by-step).


Safer standard recommendations

Standard, for their part, are safer in recommending that the three previous conditions be met simultaneously [2, 3]:

–       Overriding operating mode,

–       Hold-to-run control,

–       Reduced-energy levels.

The ISO 12100 (2010) standard adds a fourth condition in which hazardous functions may not be operated by an action, voluntary or not, on the equipment’s sensors.


What is reduced speed? Reduced force?

Certain equipment, like robots, have specific standards giving precise values to the reduced-energy levels considered safe (ex. 250 mm/s). Nonetheless, depending on the equipment, many values considered safe exist [4]. It is therefore difficult to know which value to select when designing or modifying a reduced-energy control mode. Many parameters must be considered, such as the type of control, the shape of the moving part or the parts of body exposed. In the absence of specific standards containing precise values of reduced-energy for a given equipment, there is no choice but to use comparison with known and standardized situations [5].


Example 1:

 Robot’s T1 (or learning) mode: Manual operation mode of a robot, controlled from the inside of the enclosure during its learning phase. Speed is reduced to a maximum of 250 mm/s and hold-to-run control is used in conjunction with a three-position validation device [6].


Example 2:

For adjustment operations on injection molding machine, a ‘’setup mode’’ exists that is activated by a selector which can be locked into position. The movement of dangerous parts may only be initiated by a hold-to-run control and the speed may not exceed 25 mm/s. [7].


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[1] Règlement sur la santé et la sécurité du travail du Québec, RLRQ, c. S-2.1, r. 13.

[2] Organisation internationale de normalisation. (2010). Sécurité des machines : principes généraux de conception : appréciation du risque et réduction du risque. Norme ISO 12100 : 2010. Genève : Organisation internationale de normalisation.

[3] Association canadienne de normalisation. (2017). Protection des machines. Norme CSA Z432-16. Toronto : Association canadienne de normalisation.

[4] Chinniah, Y., Aucourt, B., Bourbonnière, R. (2017). Safety of industrial machinery in reduced risk conditions. Safety Science 93, 152-161.

[5] Aucourt, B., Chinniah, Y. (2018). Sécurité des machines et mode de fonctionnement à énergie réduite – Démarche pour le choix de valeurs sécuritaires (Guide RG-1002). Tiré de

[6] Association canadienne de normalisation. (2014). Robots industriels et systèmes robotiques. Norme CSA Z434-14. Toronto : Association canadienne de normalisation.

[7] Association canadienne de normalisation. (2013). Maîtrise des énergies dangereuses : cadenassage et autres méthodes. Norme CSA Z460-13. Toronto : Association canadienne de normalisation.

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