Which of the following is NOT a critical component of an IED?

In the context of improvised explosive devices (IEDs), the critical components typically consist of a power source, a switch, and a container for the explosive material. The power source is essential as it provides the necessary energy to detonate the device. The switch acts as the trigger mechanism, allowing the device to be activated remotely or by direct action. The container holds the explosive material, helping to contain and direct the blast effect.

The inclusion of a fire extinguisher does not align with the fundamental components required to form an IED. While fire extinguishing equipment may be relevant in a broader safety context or in response to an IED incident, it is not a part of the construction or function of the device itself. Hence, it is identified as the correct answer in this scenario since it does not contribute to the operational makeup of an IED.