We can define the paper formats according to their measures and these are defined in ISO standard 216 one, which in turn includes the standard DIN 476. This applies in most of the world. I there are plenty of measures for the role, but the most used are the Serie A and to a lesser extent Serie B.

In Serie A, the most widely used format is the A4 (210x297mm) or also called "sheet" used in most printers and fotocopiadoras.

Series B is defined for intermediate sizes Series A. For example, the B4 is the intermediate size between A3 and A4.

One of the factors to take into account are the levels of protection needed and to select in an appropriate way those ideal elements for each work to be carried out.
Among them we can find security masks, which will help us protect ourselves from the particles that we can generate.

The level of protection is governed by European regulations, which must appear on each machine and depend on your ability tofiltered among other values.
This nomenclature is of the type:

FF Notation of "half filtering mask".
Gas Filter symbol against gases and their class.
P Filter symbol against particles and their class.
Reuse R (reusable) or NR (one shift).
D Optional test symbol for obstruction.

For example: FFB1 R, FFP1 NR D, FFP1 NR

The use of codesof colors on the equipment to indicate the filters is optional. If they are used, you must agree with the following table:

KIND	CLASS	COLOR	USE
TO	1,2 OR 3		Organic gases and vapors with boiling point> 65ºC
AX	-	Brown	Organic gases and vapors with a boiling point less than or equal to 65ºC. Not reusable
B	1,2 OR 3		Inorganic gases and vapors
AND	1,2 OR 3	Yellow	Sulfur dioxide, other acid gases and vapors
K	1,2 OR 3	Green	Ammonia and its derivatives
	1,2 OR 3	White	Particles
SX	-	Violet	Specific gases
NO-P3	-	blue
		White
Hg-P3	-	Red	Mercury values. Maximum duration 50 hours
		White