What minimum fire extinguisher rating is required for CNG dispensing refill areas?

The minimum fire extinguisher rating required for CNG dispensing refill areas is established to ensure adequate fire safety measures are in place for handling compressed natural gas. A rating of 20 - B:C indicates that the extinguisher is capable of effectively combating fires involving flammable liquids and electrical equipment, which are pertinent concerns in CNG operations.

A rating of 20 signifies that the extinguisher has the capacity to extinguish fires of a larger magnitude compared to those with lower ratings. Given the nature of CNG, which is a flammable gas, having a higher rated extinguisher is critical in case of an emergency, as it can deal with larger fire scenarios that may occur during dispensing operations.

The other ratings offered in the options, while providing some level of fire suppression, do not meet the required minimum capacity to manage the potential risks associated with CNG. Hence, the choice of a minimum rating of 20 - B:C is crucial for ensuring that personnel are properly equipped to handle and respond to fire incidents effectively.