Last edit: 09/05/2023
Two main International Standards supports the use of “Zero Energy” to reduce hazards in Machineries:
ISO 14118: Safety of machinery – Prevention of unexpected start-up (Latest edition: 2017)
ANSI ASSE Z244.1: The Control of Hazardous Energy Lockout, Tagout and Alternative Methods (Latest Edition: 2016)
Hazardous energy includes energies generated by Electrical, Pneumatic Hydraulic, gravity, chemical, combustion gasses (Methane) etc…
The principle of “Zero Energy”
The principle of zero energy is simple: when you need to access a confined (dangerous) area of a Machinery, isolate and dissipate all energy and prevent that somebody re-energises some part of it by placing your personal lock (Lockout). Place a Tag so that you can be contacted (Tagout). Before you start the work, make sure the part you are working on is indeed de-energised (Testout).
In countries like USA, Canada and UK, the Social Laws (equivalent of D.Lgs 81/08 in Italy) require the application of such a technique. That makes the application of the Lockout-Tagout methodology in those countries wide spread.
In Italy, like in many European Countries, the methodology is indicated in Technical standards (that are not mandatory). That makes Lockout-Tagout the exception more than the rule.
Alternative methods
Not always the LOTO methodology can be used. Consider for example the access to a dangerous area where a Robot needs to be configured using a teach pad.
In that case I have to rely upon the fact that all the movements are stopped thanks to safety loops (Interlocks – Safety logic – Contactors – Actuators) that should be in conformity with EN ISO 13849 or other functional safety standards.
That is just an example. I can use other methods that guarantee a propel level of safety, provided a genuine risk analysis is performed beforehand.
That Approach is called “Alternative Methods” in Z244.1 Here what is stated in the standard:
Lockout or tagout shall be used unless the user can demonstrate an alternative method will provide effective protection for persons. When lockout or tagout is not used, then alternative methods shall be used only after the hazards have been assessed and risks documented.
That Approach is called “Other measures to prevent unexpected start-up” in ISO 14118. Here what is stated in the standard:
Where the risk assessment shows that isolation and energy dissipation are not appropriate for an intervention (e.g. manual loading/unloading), the following measures necessary to prevent unexpected startup shall be taken as appropriate:
- measures taken in the control system to prevent the generation of start commands from unintended actuations of a start control device or other parts (e.g. sensors, power control elements), from failures in or from external influences (vibration, shocks, disturbances of the power supply) (see 6.2);
- measures taken at level A, B or C of the machine (see Figure 1 [below]) or at mechanical disconnection elements or at movingparts (immobilization), to prevent unintended start commands resulting in an unexpected startup (see 6.3).
