What must be ensured in the design of CNG facilities for ventilation purposes?

The design of CNG facilities must prioritize proper ventilation to ensure safety and compliance with regulations. Ensuring that at least one side of the facility is open enhances airflow, which is crucial for dispersing any natural gas that may leak or accumulate. Natural gas is lighter than air, so having an open side aids in ventilation, allowing any potentially harmful gases to escape rather than build up within the enclosed space.

This measure not only reduces the risk of fire or explosion but also creates a safer working environment for personnel. Ventilation is a key component of risk management in the design and operation of CNG facilities, as it helps to maintain air quality and prevent hazardous situations.

The other options do not address the fundamental requirement for ventilation in the same effective manner. A slanted roof may affect drainage and aesthetic aspects but does not inherently improve ventilation. The use of metal roofing and closed storage units could actually hinder air circulation, which is essential for managing gas emissions and ensuring the safety of the facility.