Machine Safety Acceptable Risk, Tolerable Risk, 5 Comments


Machine Safety - to understand machine safety, you have to understand the concepts of “acceptable” versus “tolerable” risk.

First, “tolerable risk” is the term used for the past several years referring to a level of residual risk for a given hazard after applying risk reduction measures. ANSI B11.1- 2009, Safety Requirements for Mechanical Power Presses, defines tolerable risk in clause 3.90.1 “Risk that is accepted for a given task (hazardous situation) or hazard”. In my opinion a more current term has come to life replacing tolerable risk as more focus continues to be directed at integrating the safety mindset into all phases of a machine life cycle.

“Acceptable risk” is the new term that is beginning to appear in many updated standards and which in my opinion more clearly represents the implied intent of both evaluation and mitigation. The assumption is that risk can never truly be totally eliminated from a hazard but that every risk should be evaluated for risk reductions measures and mitigated to the smallest amount possible.

Therefore, these updated standards are defining acceptable risk as the level at which further risk reduction will not result in significant reduction in risk or that additional expenditure of resources will not result in significant advances towards increased safety.

So, how much does this discussion matter? Isn’t the whole bottom line of the required risk analysis process really about consciously identifying hazards and reducing their risk of occupational injuries, illnesses, and fatalities? If your first response to this question is no - I strongly urge you to take anyone’s course on “Risk Assessment - 101″. Of course the answer is - YES! So, let’s stop hiding behind building columns and do what’s right for our fellow mankind.

Posted by J.B. Titus on October 12, 2009


January 16, 2010

In response to: Machine Safety Acceptable RiskFranco Tomei commented:


It appears from some of the questions that the writer has focused on a different deficition of risk that what is stated in the articel as follows;

“Definition (from article) acceptable risk as the level at which further risk reduction will not result in significant reduction in risk or that additional expenditure of resources will not result in significant advances towards increased safety”.

There is some objectivity in the definition and it is not simply up to the employer or any other individual. The requirements of the definition must be met otherwise the whole thing falls apart.

December 2, 2009

In response to: Machine Safety Acceptable RiskJB commented:

Silvio - here in the US you can find several standards mentioning acceptable risk. To mention a few - NFPA 79, 2007, ANSI B11.TR7, 2007, ANSI-PMMI 155.1, ANSI B11.1, 2009, and an article at Control Engineering

December 2, 2009

In response to: Machine Safety Acceptable RiskSilvio Melo commented:


Where can I find a Standard mentioning this subject?

October 21, 2009

In response to: Machine Safety Acceptable RiskJB commented:


The owner of a business in the US must provide a safe work place. Therefore, it can be argued that he is the first one to answer “what is acceptable?”. He may tell the engineer that his solution for a safety circuit is acceptable at Cat. 2 because he plans to mitigate the residual safety hazard further via warning signs, operator training, and steel guards.

October 21, 2009

In response to: Machine Safety Acceptable RiskStan commented:


That begs the question, “What is acceptable?” All the standards in the world can not fully answer that. What is acceptable to 1 is not to another. That is what makes “what is” so hard.

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