EMPs or Distortion Pulse are explosions that deal large amounts Distortion damage with a distance falloff. The EMP itself is a charge weapon, and the amount of damage it does (and the range it does it to) scales exponentially as it charges up. An EMP charged for 10 seconds is much more potent than an EMP charged for 5 seconds; an EMP charged for 1 second is supported by the mechanics, but the damage and range would be pretty weak.
A ship that gets hit by this Distortion Pulse will first take damage to its shields - if a shield face is brought to 0 health, the remaining damage is passed to the items in that area. The items then scale the distortion damage received based on the current level of performance throttle, so setting it to 10% would reduce the incoming damage by 90%, and turning the item off would make it perfectly immune to the distortion damage.
A missile that gets hit by this Pulse will continue to do whatever its most recent action is, which might result in it overshooting the target or spinning out. If the missile lasts long enough to recover from the distortion damage, it would resume normal behavior, but most likely it would run out of fuel and die.
A person that gets hit by this Pulse will have suit systems disabled, but the tiny components on the player suit would recover quite quickly, especially compared to what a ship would experience. This could involve glitch effects to the visor, EVA thruster errors, etc.
If you think there is a risk of a Distortion Pulse, you should keep your distance and consider managing your power to mitigate those risks. For example, if you have two power plants, you could turn one of them off to ensure it is perfectly immune to the Pulse damage, and then after the detonation disables the active power plant you could turn the other one back on to resume normal operation (at half the power availability you'd have with both power plants active, of course). Additionally, power distribution aids in distortion decay (the rate at which a component recovers from distortion damage), so setting the distribution priority can help get specific systems back online sooner.