The correct answer is option 'C' - Fast.

In order to understand why the speed of circuit interruption in a forced blast circuit breaker is fast, let's first understand what a forced blast circuit breaker is and how it works.

Definition of Forced Blast Circuit Breaker:
A forced blast circuit breaker is a type of circuit breaker that uses a high-pressure air blast to extinguish the arc formed during the circuit interruption process. It is commonly used in high-voltage applications to protect electrical equipment from damage caused by faults and overloads.

Working Principle of Forced Blast Circuit Breaker:
1. Circuit Interruption:
When a fault or overload occurs in an electrical circuit, a high current passes through the circuit breaker. This high current generates an arc between the contacts of the circuit breaker.

2. Arc Quenching:
In a forced blast circuit breaker, the arc is rapidly quenched by directing a high-pressure air blast onto the arc. The high-pressure air blast cools and deionizes the arc, extinguishing it quickly.

Reasons for Fast Circuit Interruption:
1. High-Pressure Air Blast:
The use of a high-pressure air blast in a forced blast circuit breaker ensures fast circuit interruption. The high-pressure air blast provides a strong force to cool and deionize the arc, leading to rapid arc quenching.

2. Efficient Arc Quenching:
The high-pressure air blast facilitates efficient arc quenching by creating a turbulent flow around the arc. This turbulent flow helps in breaking the continuity of the arc and aids in its extinction. As a result, the arc is extinguished quickly, allowing for fast circuit interruption.

Advantages of Fast Circuit Interruption:
1. Protection of Electrical Equipment:
Fast circuit interruption protects electrical equipment from damage caused by faults and overloads. By quickly extinguishing the arc, the forced blast circuit breaker prevents excessive current flow and minimizes the risk of equipment failure.

2. Minimization of Arc Energy:
Fast circuit interruption also reduces the energy released by the arc. The high-pressure air blast efficiently cools and deionizes the arc, reducing the duration and intensity of the arc. This helps in minimizing the arc energy, which can be detrimental to the electrical system.

In conclusion, the speed of circuit interruption in a forced blast circuit breaker is fast because of the use of a high-pressure air blast, which efficiently quenches the arc and protects electrical equipment.