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OSHA’s PSM Update: What’s Not There — Human Error
In August 2022 the United States Occupational Safety and Health Administration (OSHA) released a series of proposed updates to their Process Safety Management standard, 29 CFR 1910.119.
There was a total of 24 proposed updates, most of which were to do with tuning the existing standard, or responding to recommendations from the Chemical Safety Board, or addressing various legal issues. We have systematically evaluated each of these items in a series of blog posts that are indexed here. However, what is in some ways more interesting is thinking about what OSHA chose not to include.
This post to do with Human Error is the first in a series that discusses such items.
There are many references in the proposed updates to Process Hazards Analysis (PHA). There is also a section of the proposed updates to do with Root Cause Analysis.
Amending paragraph (m) to require root cause analysis.
(Paragraph (m) of the regulation is to do with Incident Investigation.)
OSHA wants companies to improve their ability to determine what could go wrong. Which means that they need to identify hazards, and that they need to determine the causes of those hazards.
Hazards are generally caused by some type of failure within a system. The failure could be to do with equipment, instruments or human performance.
Equipment and instrument failure is, by and large, fairly well understood. Techniques such as Failure Modes and Effects Analysis (FMEA) help identify the ways in which equipment items can fail. It is also possible to review failure rate data in order to come up with an estimate as to how often equipment or instruments will fail.
What is not understood nearly as well is the topic of human error. Yet it is almost certain that some type of human error will be involved in incidents because usually the operator being, in Trevor Kletz’ phrase, ‘the last man on the bus’ always has a chance to stop the chain of events before it culminates in an actual incident. If he or she fails to do so he or she is not to blame for the event — after all there were probably many other mistakes made by supervisors, managers, engineers and designers prior to the final operator error. (Looked at in this manner, all failures can be attributed to errors made by human beings somewhere in management chain.)
By its very nature, human error appears to be intractable: it is difficult to predict and will vary from person to person, and from day to day. For example, an operator who is normally completely reliable may turn the wrong valve for a variety of reasons such as,
He is not feeling well — maybe he has just contracted COVID, but doesn’t know it yet.
Management has downsized the work force, and he is expected to be in two places at the same time.
He is upset because he has personal problems at home.
The valves were repainted in new colors, and he was not informed.
Factors such as these make it very difficult to develop credible human error rate data.
Mistakes and Slips
There are many ways of categorizing human error — two of the most useful distinctions are between mistakes and slips.
A mistake (sometimes referred to as a cognitive error) occurs when a person acts on an incorrect train of reasoning, often because he was not properly informed as to what to do or how to do it. A mistake can be defined as follows:
A mistake is a human error that is a failure in diagnosis, decision-making, or planning.
Mistakes can be further divided into those that are ‘procedural’ and those that are ‘creative’. A procedural mistake occurs when, for example, there is a lack of clarity in the operating instructions, thus causing an operator to misinterpret them. A creative mistake occurs when a brand-new situation develops, often during an emergency, and the operator has to develop a response on the spot, often in a very short period of time.
A slip occurs when a person makes an error, even though that person knew what to do and how to carry out a task. It can be defined as:
A slip is a human error resulting from failure to carry out an intention, even though the person concerned had the capability, time, and equipment to successfully carry out that intention.
Slips usually occur during normal, routine, non-stress situations. For example, an operator may routinely take two samples from a certain section of the plant every shift, and he may have successfully performed this action hundreds of times. Then, on one occasion, he slips up and inadvertently switches the samples. Mistakes imply thinking; slips imply routine.
Worker fatigue is a common reason for the occurrence of slips.
The technique for human error-rate prediction (THERP) is used to estimate the probability of human error occurring while performing a task. From such analyses measures can then be taken to reduce the likelihood of errors occurring within a system and therefore lead to an improvement in overall levels of safety.
THERP has three components:
Error quantification, and
The results from THERP estimates can be incorporated into an overall Fault Tree Analysis.
In this short post we have just touched on some of the issues to do with human error. There is obviously a lot more that can be said. It would have been interesting had OSHA chosen to take up the topic when considering updates to its process safety management standard.
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