Gas movement is driven by a pressure gradient: higher pressure on one side pushes the gas toward lower pressure on the other side. This pressure difference provides the driving force that causes flow through a pipeline, overcoming friction and any restrictions along the path. If the pressures are equal, there’s no net flow. That’s why flow from higher pressure to lower pressure is the correct description, while flow from lower to higher pressure or flow that’s independent of pressure don’t match how natural gas moves in a system.

The concept here is how to read the specific gravity of a gas relative to air, which tells you whether the gas will tend to rise or sink in air. Specific gravity for gases is basically a comparison of densities, and in practice it’s closely tied to the gas’s molar mass. Carbon monoxide has a molar mass of about 28 g/mol, while air is around 29 g/mol. That makes the SG of CO roughly 28/29, which is about 0.97, commonly cited as near 0.97–0.98. So the option around 0.98 best represents carbon monoxide’s SG: it is lighter than air (SG less than 1), so leaks will tend to rise and disperse upward rather than pool on the floor. The other numbers imply the gas is much lighter or heavier than air (0.88 would be even lighter than CO but still not the standard value; 1.10 and 1.20 would mean the gas is heavier than air), which does not match CO’s known properties. Using 0.98 aligns with the standard data and practical understanding of CO behavior in ventilation and leak scenarios.

Cross-contamination introduces safety risks because mixing different gas streams can change what the gas actually contains. When streams with different compositions come together, the resulting mixture may become more hazardous or flammable than either stream alone. For example, introducing toxic or corrosive components into a clean gas stream can expose workers to dangerous exposures and accelerate equipment corrosion or failure. Unintended gas interactions can also lead to conditions the plant wasn’t designed to handle, such as incorrect odor levels, unexpected heat release, or pressure transients, all of which can injure personnel or damage equipment. In short, it’s not just a quality issue—it directly affects the safety of the process and the integrity of the plant. The other options don’t fit because production speed isn’t a safety concern tied to cross-contamination, and saying there are no safety concerns ignores the real hazards. Saying it only affects odorization is incomplete since composition changes can drive all the safety and equipment implications discussed above.

In natural gas pipelines, gas loses pressure as it flows because of friction and changes in elevation. To maintain flow and meet downstream pressure requirements, the gas is compressed back up to a higher pressure at intervals along the line. The machine that does this is a compressor station, which houses compressors driven by turbines or electric motors. By boosting the pressure, the station offsets the pressure drop and keeps the gas moving efficiently. The other options don’t fit this function: an Emergency Shutdown System is a safety mechanism to stop the line, an Excess Flow Valve limits flow if it’s too high, and heaters raise temperature rather than pressure.