Final answer:
The A1 classification is the safest ASHRAE refrigerant safety classification, signifying low toxicity and no flame propagation.
Step-by-step explanation:
The ASHRAE refrigerant safety classification that is considered the safest is A1. The ASHRAE safety classifications are divided into two major categories: toxicity (denoted by the letters A and B, with A being lower toxicity) and flammability (denoted by the numbers 1, 2, and 3, with 1 being no flame propagation). Therefore, an A1 classification indicates a refrigerant with low toxicity and no flame propagation, which makes it the safest option among those listed.