Which of the following is considered an abnormal operating condition?

Blowing or leaking gas is considered an abnormal operating condition because it indicates a potential safety hazard and a deviation from standard operational procedures. In natural gas operations, any escape of gas from the system is a serious concern, as it can lead to dangerous situations, including explosions, fires, and environmental hazards. Detecting gas leaks requires immediate attention to ensure the safety of personnel, equipment, and the surrounding community.

On the other hand, low pressure in the main line can sometimes be a normal occurrence depending on various factors like demand fluctuations. Normal flow of gas is precisely what is expected in routine operations and does not represent an abnormal condition. Routine maintenance of facilities is part of standard operational practices and does not indicate an abnormal situation either. Therefore, blowing or leaking gas is the only choice that directly reflects a significant threat requiring urgent response and remediation.