The blast is a response to a situation where you're threatened, cannot escape, but need to take your opponent out completely. Maybe you're with a loved one and cannot run, leaving them behind. Or maybe a quick escape just isn't an option. The blast is simply a continuous, high pressure assault, and an infinite variety of techniques can be used. In that sense, every attack or counter attack is a blast. For the conditioned response however, you should choose one entry or initial technique that suits you well and works against a great variety of attackers.
The blast as a conditioned response should be trained against a partner who approaches you in a threatening manner and gives you no chance or way to escape. As soon as he gets almost close enough to attack, launch into your blast.
One of my favorite entries to the blast is the smack and hack. It's extremely effective, keeps you very well covered, and there are a huge variety of follow ups. Below you'll find one example sequence of the smack and hack used for the blast.
Another example of the blast, as an interception or counter attack vs. when you're able to attack first, is the low jab intercept.
See more self defense techniques, or more from the Fundamental Five: