Valve interlocks, or captive keys, employ locks that prevent the movement of valves and unique keys. Keys will only be released according to a desired valve operating sequence, preventing operators from operating valves incorrectly. The suggested Probability of Failure on Demand (PFD) for captive key systems is 0.01. Other valve isolation methods, such as LOTO, also employ keys. Proper management of captive keys is safety-critical and should prevent undesirable, costly, and even dangerous situations.
The effect of poor key management procedures
Depending on different factors like the type of key missing (where a ‘master key’ missing will pose a higher risk), or the possibility of a safety-critical valve being in the incorrect position, you can assess the risk associated with inadequate key management practices. To facilitate the management of keys, various products are available today, ranging from coded key cabinets, to electrical cabinets, and digital key management systems. Often, these products are used in line with operational procedures.
Key management procedures in practice
Let’s examine two cases from the industry. The first case is of a facility with around 400 captive key systems, where keys are segregated based on criticality, and the operators must follow different unwritten procedures to take and return keys from the cabinets. In another example, a facility with approximately 4000 captive key systems employs a 13-step process, that must be followed per transaction to manage keys. Many facilities do not follow defined valve interlock key management practices. Consequently, one might question whether these procedures are effective and sufficient to meet the calculated PFD of 0.01. Also, how do compromised key management procedures impact the efficiency of the operators, and how does missing a master key after a turnaround impact your Pre-Startup Safety Audit (PSSA)?
Enhancing process safety through effective key management
Effective key management practices should uniquely identify the operator for each key transaction and actively prevent unauthorized actions, such as untrained personnel or someone taking a master key. These practices should ensure operators have access to the necessary information to perform procedures correctly. Alerts must be triggered for any deviations from proper practices. Additionally, reports should be available to audit all transactions, such as tracking a missing key or monitoring the frequency of procedures. Combined with captive key systems, effective key management provides accurate valve open and closed status and system status information, such as maintenance activities.