Personal Protection
The letters P, R, W or X indicate that a full chemical protection suit and breathing apparatus should be worn. The letters S T Y and Z may on occasion appear. These reversed characters indicate that breathing apparatus need only be worn if the substances are involved in a fire.
Frequently in text these appear in a box, ie. S T Y or Z to indicate that they are to read as a white letter on a black background.
Contain or Dilute
The letters P, R, S and T indicate dilution while W, X, Y and Z indicate containment.
Both seek to reduce the hazard or prevent escalation of the incident.
'Contain' attempts to achieve this by confining the material within finite bounds and minimising environmental impact. It also allows recovery of the material where such a procedure is safe and practicable.
'Dilute' attempts the opposite and seeks to disperse the material as diffusely as possible thereby reducing environmental impact.
In cases of spillage without fire where the medium is either water jets or water fog and containment indicated, water should not be applied.
Violent Reaction
The letters P, S, S, W, Y, and Y indicate that a violent reaction may occur through such occurrences as decomposition, ignition of vapours, acceleration of combustion due to involvement of an oxidising agent or reaction with water.
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