NFD
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Noise Flash Devices.
Otherwise known as Flashbangs, Stun Grenades, Distraction Devices, the terms all refer to such hand deployed explosive munitions as NICO 9's, Def Tech 25's, and M-84's. (note, Concussion grenades are not NFD's, but seperate munitions)
NFD's are normally deployed just inside of a doorframe, where any hostiles are liable to have their eyes. They effectively blind and disorientate anyone who is within effective range, however they are non lethal, and so are safe to use in hostage rescue situations.
The basic NFD works on a 1.5-3 second fuse. The operator arms it, normally like a normal grenade (Pull ring and release safety handle as the device leaves the hand). Once activated, and the fuse is burned out, the device creates a brilliant flash (normally with the use of such materials as magnesium in the main charge) and a deafening bang. This flash has the effect on observers of basically paralysing their optical nerves in the eyes, and the result is dependant upon the person affected, but can be anything from a total white out, to what is often described as a still, or freeze frame, where the paralysation causes the optical nerve to continue to transmit the last seen image before the flash, regardless of where the person is looking, or if their eyes are open or closed. This can last up to 30 seconds. The Bang causes a ringing in the ears, lessening the ability to orientate oneself on sounds around you. This disorientation is further compounded by the fact that the blast is enough to disrupt the water in the ear canals that the brain uses to register 3D position and balance.
The NFD is assured as being less lethal by having ports in a strong outer case. This allows the blast to exit the device in a controlled manner, rather than blowing the case apart. Earlier NFD's had one big port in the bottom (such as the Def-Tech 25). This had the effect of turning the munition into somewhat of a missile howewever as the charge's force was controlled out of the bottom. This was understandably seen as a danger, especially after one or two incidents with the grenades embedding themselves in walls (and on occasions, people). This bought about the advent of Multi-Port Devices, in the case of later Def Tech's, holes were added to the top of the case to counter the thrust from the base. Deviced designed more recently often have 9-12 ports around the sides, rather than in the base, thus successfully dispersing the energy of the blast.
NFD's require a responsible user, as the potential for harm to self or others is still there (Prime example of what can happen being the fire that broke out during the SAS Op. Nimrod). NFD's should not be deployed within a few meters of furniture or barricades, for instance, and should be deployed away from people, rather than next to them where possible, due to this potential for harm, and also the risk it can put peoples ears under (i.e. permanant damage from ruptured eardrums).
Real world NFD's are rarely seen on skirmish fields, and as far as I am aware, never sold at sites for standard use. A common substitute is the Mk5 or Mk9 series of pyrotechnics.
