Logic Implementation
You have so many ways to do it, depends on your constraints.

Let's say you work with 7400 TTL gates and you want to minimize the number of chips.

But first you have to clarify what you really want.


  I have 4 inputs. A being ON/OFF switch. B is an Inibitor. C is an Emergency and D is not an adequate ocasion.
  
  In order to turn off the lamp I have to meet 2 conditions.
  
  Condition 1: Switch is ON (A), Inibitor is OFF (B) and the ocasion must be adequate (NOT D).
  
  Condition 2: Emergency is ON (C). This one is independent and will always turn on the light as long as it is activated.


There are so many negations in there you're getting yourself confused.
I will assume you do not have a hidden parameter still, i.e., being a signal light, a condition in which the signal light should light up. Then you can override and turn it off by switching ON the override switch A, if the following conditions are met:


it's not an emergency, E = false
it's not an otherwise inadequate situation to turn lamp off, D = false
the light-off-inhibitor B is not on, B = false


And now written this way you notice that when any of the B, D, or E are true, then the light is on, L = true.  So that means B, D, and E are simply OR-ed together to turn L on. 

Otherwise switch A on/off is just inverted to light off/on. So if you invert that switch also, you have all 3 conditions OR-ed together and you can simply say:

L := (NOT A) OR B OR D OR E

So you can put these together with a 74LS32 quad 2-input OR gate: 

L := ((NOT A) OR B) OR (D OR E)







simulate this circuit &ndash; Schematic created using CircuitLab

and you have used 3 of the 4 OR gates in the chip. Since A is a switch, and not a signal, you can get the inverted state of the switch without needing any other inverter.

You can try using only NAND gates but making only one OR requires 3 NAND gates already, so you do not gain anything. 

Since you stated your conditions somewhat vaguely (not clear if "adequate situation to turn off" or "not inadequate situation to turn off" is positive or negative signal) but if you're going to need 2 chips, you might as well use the 74x32 and the 74x04 hex inverter, to be able to negate any of your inputs and output as needed.