Which safety measure is crucial when working with CNG?

Answer: C — Proper ventilation

The emphasis on proper ventilation when working with compressed natural gas (CNG) is critical due to the properties of the gas itself. CNG is lighter than air; in the event of a leak, it rises and can accumulate in higher areas, which presents a risk of explosion if ignited. Adequate ventilation ensures that any escaping gas disperses quickly and does not reach a concentration that could become hazardous. This safety measure is essential in any environment where CNG is present to mitigate the risks associated with its flammability. In contrast, wearing flip-flops does not provide the necessary protection or support in environments where CNG work occurs, making it an inappropriate choice. Working in enclosed spaces can compound the dangers associated with CNG, as limited airflow could lead to gas accumulation. Using metal tools is also not a universally safe practice, as certain tools may spark and ignite gas if they contact flammable materials. Thus, ensuring proper ventilation is the most effective way to promote safety when handling CNG.