Which of the following conditions is a common heater trip?

• A. High fuel gas pressure, low fuel gas pressure, and low process flow
• B. High air temperature, no flame
• C. Low water pressure, high water temperature
• D. Excess oxygen with high flame speed

Answer: (A)

The main idea is that fired heaters are protected by interlocks that trip when fuel delivery and heat load are not in the safe, controllable range. Abnormal fuel gas pressure—whether too high or too low—directly threatens flame stability and safe operation, so the control system will trip to prevent unsafe firing. If the gas pressure is off, the burner can’t maintain a stable flame or can run into fuel-control issues, which makes a trip the safest action.

Low process flow is also a common trip trigger because it means there isn’t enough load on the heater to absorb the heat being produced. Keeping firing when the process flow is too low risks overheating the heater tubes and the process stream, so the safety system cuts off the burner.

The other described conditions aren’t as typical for a standard heater trip. A scenario with high air temperature and no flame points to a flame-out situation, but the pairing isn’t a standard, broad-trip signal on its own. Low water pressure or high water temperature is more characteristic of boilers or heat exchangers using water as the process medium, not a fired heater. Excess oxygen with high flame speed is a combustion abnormality, but not the most common automatic trip signal for typical heater protection.