151: Individual Control/Display/Alarm Issue
Definition/Typical Issues
Did inadequate equipment controls or control systems (e.g., push-buttons, rotary controls, J-handles, key-operated controls, thumbwheels, switches, joy sticks) contribute to the occurrence? Did the control fail to provide an adequate range of control for the function it performs? Was the control inadequately protected from accidental activation? Did one switch control a number of parameters or have different functions under different conditions?
Did inadequate displays or display systems (e.g., gauges, meters, light indicators, graphic recorders, counters, and video display terminals) contribute to the occurrence? Did the display fail to provide all information about system status and parameter values needed to meet task requirements? Did the configuration of the display make information difficult to see or to interpret? Was it necessary for the user to convert information presented by the display prior to using it? Did unnecessary or redundant information contribute to the error?
Was there a failure to develop alarms for critical device failures? Are alarms difficult to hear? Are alarm tiles or computer displays difficult to read? Are alarms poorly arranged or formatted to support situation assessment? Was there a failure to prioritize alarms in terms of criticality to safety and immediacy of required crew response? Are there inadequate controls for alarms, including acknowledgment and reset? For computer-displayed alarms, was there a failure to present alarms in the order in which the initiating condition occurred? Is there alarm overload in the workplace?
Note 1: Arrangement of controls is addressed by the Control/Display/Alarm Integration/Arrangement Issue (#152) node. The location of controls is addressed by the Awkward/Inconvenient/Inaccessible Location of Control/Display/Alarm (#153) node.
Examples
Example 1
- The operator of a remotely driven crane inadvertently struck a machine with the load being moved. The keys on the keypad he was using to operate the crane were very small and close together. The operator's fingers, even though they were average size, were too large to accurately press one button without inadvertently pressing the surrounding keys.
Example 2
- During an emergency, an operator made the incident worse by increasing flow instead of stopping flow. All flow controllers in the plant were moved counterclockwise to reduce flow except for the one involved in this incident. It was moved clockwise to reduce flow. This violated the standard practice at this plant.
Example 3
- An operator made an error in reading a meter because of the unusual scale progression. Instead of a scale with major markings divided by units of five (i.e., 5, 10, 15, 20), the scale was divided into units of six (i.e., 6, 12, 18, 24).
Example 4
- A digital display was used to monitor the flow rate of a system. The system responded slowly to control changes. This required the operator to write down values at various times to create a time log. A chart recorder would have been a more appropriate type of display.
Example 5
- Alarms cannot be heard in the cogeneration unit above the noise when it is in operation. No visible indicator is provided. Therefore, alarms are not communicated to personnel working in the cogeneration unit when the unit is in operation.
Example 6
- An operator set the flow rate improperly. The procedure specified the flow rate in gallons per minute. The display indicated pounds per hour.
Example 7
- Operators did not know that a regeneration was taking place in a treater. No indication of the regeneration status was displayed on the computer screen. They just thought that one of the valves had been left open. Closing the valve interrupted the regeneration process. As a result, the treater failed during subsequent use.
Typical Recommendations
- Configure controls such that it would be difficult to accidentally activate them.
- Ensure that the device/display allows the necessary range of control (e.g., 0-100 GPM control dial would be inappropriate if the flow sometimes required settings as high as 110 GPM).
- Ensure that sensitivity of controls allows an operator to quickly and accurately make process changes.
- Ensure that displays provide enough information about the process so that the operators can adequately control it.
- Configure displays so that they are easy to read and interpret.
- Provide direct display of the necessary parameters so that operators do not have to convert the information for it to be usable.
- Display only the information that is necessary/helpful to safely and efficiently control the process.
- Avoid the use of dual-purpose controls. Provide one control for each parameter being controlled.
- Equipment or systems that are critical to safe operation should be equipped with failure alarms.
- Make alarms for critical systems and equipment audible, visible, and easy to read to allow personnel to easily assess the situation.
- Alarm recording systems should record alarms in order of occurrence.
- Place flashing lights in locations where an audible alarm cannot be heard over the surrounding noise.
Cross-References
| Version 10 Element(s) | |
|---|---|
| Node ID | Node Name |
| 141 | Controls/Displays LTA |
| Maritime Element(s) | |
|---|---|
| Node ID | Node Name |
| 166 | Individual Control/Display/Alarm Issue |
| 155 | Alarm/Signal Issue |