Below is a short video of a 100 square metre space with packing increasing from 1 person per square metre to 10 people per square metre. This serves to illustrate how the crowd may look in low risk and high risk situations.
The word comes from the Greek euangelion, or good news. The gospel was considered the good news of the coming Kingdom of Messiah, and of redemption through the life and death and resurrection of Jesus, the central Christian message.
Meaning explosion is from 1630s; that of noisy party, good time is from 1953, American English slang. Sense of strong current of air for iron-smelting (1690s) led to blast furnace and transferred sense in full blast the extreme (1839). Blast was the usual word for a smoke of tobacco c.1600.