Inherently Safer Technology (IST) and Inherently Safer Design (ISD) are approaches that seek to avoid hazards in processes instead of controlling them. Inherent safety approaches change the process to eliminate the need for elaborate safety systems and procedures by eliminating the hazard completely or reducing its magnitude sufficiently using a means for hazard elimination or reduction that is inherent in the process, that is, permanent and inseparable from the process.
Inherent safety approaches include:
Elimination - Remove the hazard altogether, e.g. change to a different process
Substitution - Replace with a less hazardous material, e.g. use sodium hypochlorite instead of chlorine
Abatement - Reduce the quantity stored, used, or generated, e.g. reduce stored inventories
Attenuation - Modify a process to operate under less hazardous conditions, e.g. reduce operating pressure
Dilution - Mix with less hazardous material, e.g. handle sulfuric acid rather than oleum
Isolation - Move further away from sensitive receptors, e.g. relocate a work station to increase separation distances
Some practitioners use an alternative classification of inherent safety approaches:
Minimize - Use smaller quantities of hazardous materials
Substitute - Replace a hazardous material with one that is less hazardous
Moderate - Use less severe operating conditions
Simplify - Eliminate opportunities for errors by eliminating the need to add safeguards
This is sometimes referred to as the MSMS classification of inherent safety approaches.
Inherent safety measures can be categorized as:
First Order - A measure that eliminates a hazard, e.g. substituting a toxic chemical with an alternative chemical that can serve the same function but is non-toxic
Second Order - A measure that reduces the severity of a hazard or the likelihood of a release, without the use of add-on safety devices, e.g. redesigning a high-pressure, high-temperature process to operate at ambient temperatures and pressures.
Inherent safety approaches are most effectively applied at the process design stage but they are can also be applied to existing processes. Here are some examples of inherent safety approaches for existing processes:
- Increasing pressure rating of blinds
- Imposing design limits on pumps to restrict the amount of overpressure that is possible
- Using thicker vessels
- Using refrigerated materials under atmospheric pressure instead of under pressure
- Using hot water or steam for heating instead of flammable oil
- Piping in chlorine
- Generating SO3, not using oleum
- Replacing natural gas with nitrogen for blanketing
- Replacing one large storage vessel with several smaller ones
- Moving vaporizers (e.g. chlorine) closer to the liquid source
Inherent safety is at the top of the hierarchy of hazard controls. It should be the first choice for risk reduction in processes.
Primatech can assist you with all your process safety needs. Please contact us for further information.
