API Publ 770:2001 pdf download.Reducing Human Errors Improving Human Performance in the Process Industries
2.1 DEFINITION OF HUMAN ERROR
Every task that must be performed by a human is an opportunity for error. But even though neither two people (nor even one individual) will perform the same task in exactly the same way twice, minor variations in the performance of a task are usually inconsequential. Only when some limit of acceptability is exceeded is a variation considered a human error. Thus, a practical definition of human error is any human action (or lack thereof) that exceeds the tolerances defined by the system with which the human interacts. Any discussion of human error must consider the specific actions and limits involved in a particular task. For example, an operator might be told to add 10 pounds of catalyst after a batch reactor is heated to 200 degrees. The operator can add more or less catalyst; add catalyst sooner or later; add the catalyst quickly or slowly; add a different catalyst; or forget to add any catalyst at all. The operator might also choose a blue or red scoop to measure the catalyst. Any of these variations is inconsequential unless it has the potential to cause a runaway reaction (accident), to extend the processing time (production loss), or to generate off-specification product (quality problem). Only then would the variation be considered a human error. Unfortunately, the limits on human performance are seldom well defined until someone has exceeded them at least once under circumstances that resulted in an actual problem. In general there are two types of human errors: unintentional and intentional. Unintentional errors are actions committed or omitted with no prior thought. We typically think of these as “accidents”: bumping the wrong switch, misreading a gauge, forgetting to open a valve, spilling coffee into the control console, and so forth. If the worker intended the correct action, but simply did it wrong, the error is sometimes called a “slip”; if the worker forgot to perform the action, the error is sometimes called a “lapse.”Intentional deviations (errors) are actions we deliberately commit or omit because we believe, for whatever reason, that our actions are correct or that they will be better (i.e., quicker, easier, safer, etc.) than the prescribed actions. When workers misdiagnose the true cause of an upset, they will intentionally perform erroneous actions as they attempt to respond. For example, operators on other interconnecting oil platforms actually worsened the fire on Piper Alpha in 1988 because they did not understand what was happening and did not respond appropriately. Other intentional deviations are “shortcuts” or “violations” that are not recognized as human errors until circumstances arise in which they exceed the system tolerances. Examples of such errors include failing to electrically ground containers of flammable liquids, attempting to restart a furnace without purging the firebox, adding a little extra catalyst to accelerate the start of a reaction, and so forth.
API Publ 770:2001 pdf download
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