Usually there will already be numerous ways in which you seek to prevent the top event from occurring.
The addition of these controls to the bowtie is the next step. The controls would look at two aspects of threat management:
- eliminating the threat completely, therefore making sure the threat is not present
- preventing the threat from developing into a top event if the threat does become “live”.
In the example of driving a car on a busy motorway, to eliminate our threat of a tyre blow out, the car owner would conduct regulator tyre inspections to identify any potential issues to lead to a tyre blow out. If our threat becomes “live” and a tyre blow out occurs, our preventative control could be driver steering into the skid to keep control
Additional Guidance (relevant to Prevention and Recovery Controls):
“Any measure taken which acts against some undesirable force or intention, in order to maintain a desired state.”
Traps and Tips
- Trap: Control descriptions that are too generic e.g. control: ‘ATC’.
- Tip: Describe what the control actually does with the reader in mind e.g.: ‘ATC detect incorrect presence on the runway and issue avoiding instructions’. Try to include the action that takes place to interrupt the sequence of events.
- Trap: Incorrect level of detail for diagram elements.
- Tip: When deciding the level of detail to include for the description of any diagram element there are several important considerations:
- Too little detail.
The diagram might be referred to by people separated by time and location from the author (e.g. bowties are often used as a stand alone poster). Sufficient detail should be included in the element descriptions so that the reader can generally understand the author’s intention without reference to additional explanatory material.
- Too much detail.
The competing consideration for an appropriate level of detail is that the descriptions should not be overly convoluted or lengthy. Diagram elements may be thought of as risk exclamation marks and by remaining succinct, their communication benefits are maximized. Normally one sentence should suffice.
- Trap: Not including poor quality controls.
- Tip: Include controls that are generally considered to be in place even if they have very poor effectiveness. Using colours to depict control effectiveness will highlight these areas for potential improvement.
See Recovery Controls for more additional guidance relevant to prevention controls