Which of the following is a type of Abnormal Operating Condition (AOC)?

The choice that identifies a type of Abnormal Operating Condition (AOC) is associated with unauthorized operation of the head service valve. An AOC is defined as a situation that poses a potential hazard or abnormality in the operation of gas systems that could affect safety. The unauthorized operation of the head service valve indicates that someone is tampering with a critical component of the gas system, which could compromise the integrity and safety of the entire system. This action is considered abnormal because it deviates from standard operational protocols and can lead to dangerous situations, such as leaks or unintended gas flow, thereby raising safety concerns requiring immediate attention.

In contrast, properly installed plumbing and uniform gas flow across appliances represent normal conditions and are indicative of an effective and safe gas piping installation. Routine maintenance actions are typically carried out to ensure that the system remains in good working order and do not fall under the category of abnormal conditions. Thus, these responses do not reflect the criteria necessary to categorize them as AOCs.