LPG odorization: Ethyl mercaptan is added to Doctor-negative LPG to aid leak detection by odor. What is the typical target treat rate (ppm by volume) used in practice?

Introduction / Context:
LPG is naturally odorless. For safety, an odorant such as ethyl mercaptan is added so even small leaks are detectable by smell in domestic and industrial use.

Given Data / Assumptions:

• Product: Doctor-negative LPG (sweet, low sulphur).
• Odorant: ethyl mercaptan added at a controlled trace level.
• Units: parts per million (ppm) by volume equivalent.

Concept / Approach:
Odorization balances detectability with handling safety and product quality. Regulatory and industry guidance typically specify a low two-digit ppm range to ensure recognizability without excessive sulphur addition.

Step-by-Step Solution:

Verification / Alternative check:
Operational guidelines and national safety codes often cite approximately 20–50 ppm as typical treat rates, confirming the order of magnitude.

Why Other Options Are Wrong:

• 1 ppm: Too low for reliable human detection in varied conditions.
• 5000 / 10000 ppm: Excessive and impractical; would severely affect sulphur specification and odor intensity.

Common Pitfalls:
Confusing mg/m^3 and ppm or assuming higher is always better; overdosing has drawbacks.

Final Answer:
50