Substitution is usually the least expensive and the most positive method of controlling hazards and should always be the first engineering hazard control measure considered. Minimization should always be the next engineering control measure attempted after examining substitution followed by the consideration of isolation. Isolation is particularly useful when the material, equipment or process requires minimal contact or manipulations. When these previously mentioned control methods are not feasible, ventilation is the next desirable engineering option. The two types of ventilation are typically termed local exhaust and general ventilation .
Local exhaust is always the preferable ventilation method but is typically more costly.
Because they primarily address the human element of hazard controls, they are of vital importance and are always used to control chemical hazards. In some situations, PPE may be the only reasonable hazard control option, but for many reasons it is the least desirable means of controlling chemical hazards. PPE users must be aware of, and compensate for these undesirable qualities. PPE does not eliminate hazards but merely minimizes damage from hazards. The effectiveness of PPE is highly dependent on the user.