Leak detection for ammonia (R-717) refrigeration systems: Which method is specifically suitable for identifying ammonia leaks in practice?

Introduction / Context:
Leak detection is a critical safety task in refrigeration plants. Different refrigerants require different techniques because their chemistry and safety classifications vary. Ammonia (R-717) is toxic and mildly flammable; it also has a sharp, penetrating odour, making it detectable at low concentrations, but reliable confirmation methods are still necessary.

Given Data / Assumptions:

• System refrigerant: ammonia (R-717).
• Plant operating at typical industrial conditions.
• Technician has access to basic field tools for leak testing.

Concept / Approach:
Ammonia reacts with products of sulphur combustion to form white fumes (ammonium salts), so a gently smoking sulphur stick held near a suspected joint or valve will visibly indicate an ammonia leak. In contrast, a halide torch is intended for halogenated refrigerants (e.g., R-12, R-22) and is not appropriate for ammonia. Soap-and-water bubble testing can work generally, but it is a generic technique and not the primary textbook answer for ammonia-specific identification.

Step-by-Step Solution:

Verification / Alternative check:
Industrial safety manuals and HVAC textbooks consistently list sulphur sticks or litmus paper (turns blue) for ammonia. Modern plants may also use fixed gas detectors, but the foundational field method remains the sulphur stick indication.

Why Other Options Are Wrong:

• Halide torch: Not suitable for ammonia; designed for halogenated refrigerants.
• Soap-and-water only: Works in general, but the question asks the method used for ammonia—sulphur sticks are the classic targeted choice.
• All of these: Incorrect because halide torch is inappropriate for ammonia.
• Ultrasonic only: A possible modern tool but not the only valid or standard classroom answer.

Common Pitfalls:
Using the same leak detector for all refrigerants; ignoring chemical compatibility and safety guidance.

Final Answer:
Sulphur sticks (white fumes formation)