CanadaComplementary Protective MeasuresControl FunctionsHierarchy of ControlsInherently Safe Design

Study of Machine Safety for Reduced-Speed or Reduced-Force Work


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Own­er: Doug Nix

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Last Updated: 06-06-2018 16:40


ABSTRACT The haz­ards asso­ci­ated with the mov­ing parts of indus­tri­al machines are known to be the source of ser­i­ous and even fatal acci­dents. The pur­pose of sec­tion 189.1 (pre­vi­ously 186) of the Que­bec Reg­u­la­tion respect­ing Occu­pa­tion­al Health and Safety (ROHS) is to provide guid­ance for machine main­ten­ance, repair and adjust­ment work, fur­ther to sec­tion 182, which gov­erns pro­duc­tion work by pro­hib­it­ing access to haz­ard zones and ensur­ing that mov­ing parts are stopped when work­ers enter these zones. The focus of this research pro­ject was the applic­a­tion of ROHS sec­tion 186. The first object­ive was to assess the state of know­ledge and recom­mend­a­tions in the lit­er­at­ure on reduced-energy modes of oper­a­tion, espe­cially in terms of speed, force, pres­sure and tem­per­at­ure val­ues. The second object­ive was to under­stand, through fact­ory vis­its, how ROHS sec­tion 186 is being imple­men­ted. A review of the lit­er­at­ure revealed a wide vari­ety of recom­mend­a­tions with respect to redu­ceden­ergy levels. The recom­mend­a­tions, chiefly based on stand­ards and closely related to a spe­cif­ic con­text, are gen­er­ally presen­ted with accom­pa­ny­ing sup­ple­ment­ary con­di­tions. A reduc­tion in energy alone is often not suf­fi­cient to reduce the risk. Fact­ory vis­its have shown that the vari­ous con­di­tions pre­scribed in ROHS sec­tion 186 are some­times hard to meet sim­ul­tan­eously. Safe­guards, includ­ing the reduc­tion of energy levels, are there­fore a com­prom­ise between dif­fer­ent con­straints (related to job needs, the machine itself, pro­duc­tion require­ments, etc.) and risk reduc­tion in order to pre­vent or reduce poten­tial harm. Last, the study revealed that reduced-energy val­ues depend on many factors and that the wide vari­ety of pos­sible situ­ations makes it neces­sary to con­duct an in-depth risk ana­lys­is. The applic­a­tion of ROHS sec­tion 186 is there­fore an integ­ral part of the risk assess­ment and reduc­tion pro­cess for tasks where work­ers have no altern­at­ive but to enter the zone where machine parts are in motion. The pur­pose of this pro­cess is to achieve a level of risk com­par­able to that con­tem­plated in ROHS sec­tion 182, by tak­ing pro­tect­ive meas­ures that will com­pensate for open­ing a guard or start­ing up the machine. These pro­tect­ive meas­ures are based on three prin­ciples: reduce harm, increase the pos­sib­il­ity of avoid­ing harm and reduce expos­ure to the haz­ard. Yet the issue of determ­in­ing reduced-energy levels remains unre­solved. Gen­er­ally speak­ing, when the lit­er­at­ure recom­mends val­ues, if the situ­ation in ques­tion cor­res­ponds exactly to the con­text described in the lit­er­at­ure, then design­ers may use these same val­ues. On the oth­er hand, when no ref­er­ence is avail­able, the determ­in­a­tion of a tol­er­able energy level must be based on more extens­ive thought and ana­lys­is. Only a thor­ough com­par­is­on of the con­text of the pro­pos­als made in the lit­er­at­ure and that of the real situ­ation will allow extra­pol­a­tion of the recom­mend­a­tions to com­par­able, but not identic­al situ­ations. A risk ana­lys­is must be con­duc­ted. The study iden­ti­fied some ref­er­ence points or factors that will provide guid­ance to design­ers and users as they ana­lyse spe­cif­ic cases and try to decide on the most appro­pri­ate val­ues for reduced speed, force, kin­et­ic energy and con­tact pres­sure.

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