The loop system is sometimes filled with which gas?

• A. Nitrogen
• B. Helium
• C. Argon
• D. Oxygen

Answer: (B)

When a loop system is purged or checked for leaks, you want a gas that won’t react with the system and can reveal leaks easily. Helium fits that need perfectly because it is inert and nonflammable, so it won’t cause safety or corrosion concerns. Its molecules are very small, so they diffuse through tiny gaps that air might not pass through, making leaks easy to detect with a helium leak detector. This combination—safe to use in the system and easy to trace for leaks—makes helium the preferred choice for filling and testing loop systems. In comparison, oxygen is reactive and dangerous in many contexts; argon and nitrogen are inert but don’t offer the same ease of leak detection, with argon being denser and less practical for this purpose.