Page 103 - Occupational Health & Safety, July 2018

Risk is the combination of the probability of occurrence of harm and the severity of that harm. In TR R15.306-2016, Risk is deter- mined by three criteria:
■ Injury Severity is a function of the degree of estimated harm due to each hazard while a person is performing a task. Severity has three ratings: S3 (Serious), S2 (Moderate), and S1 (Minor).
■ Exposure is a function of the estimated incidence of expo- sure (either frequency or duration) to the hazard. Exposure has three ratings: E2 (High), E1 (Low), and E0 (Prevented).
■ Avoidance is an assessment of a person’s ability to sense and elude a hazardous situation. Avoidance has three ratings: A3 (Not possible), A2 (Not likely), and A1 (Likely).
The combination of Severity, Exposure, and Avoidance yields the initial Risk Level (see RIA TR R15.306-2016, Table 2).
Once the initial risk level is determined, the user selects one or more risk reduction measures. Following the Hierarchy of Risk Reduction Measures (RIA TR R15.306-2016, Table 3), the risk re- duction measures are:
■ Elimination (i.e., eliminate the hazard)
■ Substitution (i.e., substitute the hazard with a lesser hazard)
■ Limit Interaction (i.e., reduce or eliminate interaction be-
tween the hazard and the person)
■ Safeguarding (Safeguards and Safety-Related Parts of the
Control System, or SRP/CS)
■ Complementary Protective Measures (measures that may
reduce the severity of injury, such as emergency stops, enabling devices, and energy isolation)
■ Information for Use (Warnings and Awareness Means, Ad- ministrative Controls, PPE)
Note that according to TR R15.306-2016, neither Complemen- tary Protective Measures nor Information for Use may be used un- til or unless the risk level is or has been reduced to LOW or NEG- LIGIBLE.
The residual risks resulting from the risk reduction measures chosen are as follows:
■ If Elimination is used, then all values for Severity, Expo- sure, and Avoidance are reduced to their lowest rating levels, S1 and E0 (note that once Exposure is eliminated, Avoidance is no longer applicable).
■ If Substitution is used, then Severity is reduced, but Expo- sure and Avoidance remain unchanged. (Note that the 2014 ver- sion of TR R15.306 stated the following: “Exposure to a hazard or avoidance of a hazard does not impact the severity of a potential in- jury.”) The level of Severity reduction depends on the substitution, and the substitution must meet the criteria for Substitution shown in TR R15.306-2016. For example, suppose you substitute a con- centrated acid (with an initial Severity rating of S3) with a weaker acid. The user need only determine the resulting Severity rating (S2 or S1) of the weaker acid.
■ If Limit Interaction is used and human interaction is elimi- nated, or we automate the tasks or the material handling, then Exposure is reduced to E0 (and, therefore, Avoidance is no longer applicable), but Severity remains unchanged.
■ If Limit Interaction is used and human interaction is re- duced, then Exposure is reduced one level (as long as it meets the criteria for Exposure), but Severity and Avoidance remain unchanged.
■ If Safeguarding is used, then Exposure is reduced to E0 (and, therefore, Avoidance is no longer applicable), but Severity remains unchanged.
■ If Complementary Protective Measures or Information for Use is used, then Avoidance is reduced one level (as long as it meets the criteria for Avoidance), but Severity and Exposure re- main unchanged.
Graphically, the results of using Elimination, Substitution, Lim- it Interaction, or Safeguarding are illustrated as follows:
As stated previously, neither Complementary Protective Mea- sures nor Information for Use may be used until or unless the risk level is or has been reduced to LOW or NEGLIGIBLE. The follow- ing graphic illustrates the results of using them once the initial risk has been reduced to LOW or NEGLIGIBLE by Elimination, Sub- stitution, or Limit Interaction (known collectively in TR R15.306- 2016 as Inherently Safe Design Measures) or Safeguarding:
Note that while the use of Complementary Protective Measures and Information for Use will certainly improve safety, unfortunate- ly, in most instances, the resulting residual risk level will not change from LOW to NEGLIGIBLE. For example, suppose, after employ- ing Safeguarding, the risk is S1, E2, A3 (which is LOW). You then employ Information for Use. The resulting risk is S1, E2, A2, which is still LOW.
Gary J. Garrahan (gary.garrahan@wonderful.com), CHMM, CMSE®, is Manager of Machine Safety for The Wonderful Com- pany. He presented this topic at the 2015 RIA National Robot Safety Conference in Pittsburgh, Pa.
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