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ioFIRST
A quick and reliable screening tool for addressing health, safety, and environmental hazards.
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Key
Features
ioFIRST The hazards addressed by ioFIRST are divided into
three categories:
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Toxic Vapor Dispersion
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Fire and Flammability
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Vapor Cloud Explosion Hazard
In this analysis, a hazard exists where direct or indirect effects of the
considered hazardous material events are expected to result in fatalities. For
each of the three hazard categories, scoring algorithms have developed to
reflect the maximum hazard distances from the release.
In order to minimize the required user input and difficulty of implementation,
an effort was made to limit the number and complexity of the models included in
ioFIRST. Simplifications have been made by assuming the "most likely" or
"conservative" conditions, where conservative conditions produce a "worst
credible scenario". It is important to note that for the events considered by
ioFIRST, the hazard scores are treated with equal weight regardless of
likelihood of the associated events occurring.
The toxic vapor dispersion hazards are those caused by inhalation of airborne
hazardous concentrations of toxic vapor. This does not include hazards due to
skin or eye contact or ingestion. This model calculates the downwind distance
within which vapor concentrations exceed a user specified concentration limit.
The fire and flammability hazard evaluation considers the effects of thermal
radiation resulting from pool fires and fireballs. While other events produce
fire hazards, such as flame jets, these have not been explicitly included since
their hazard areas are generally within those estimated by ioFIRST. Solid
material fires are also omitted.
Distances to overpressure hazards due to ground level unconfined vapor cloud
explosions are estimated by the model. Explosions due to explosives, dusts, and
tank over-pressurization are not currently included.
The maximum hazard score associated with each process or activity at a site is
adjusted by a value representing the exposed population. This value is based on
the number of people working at the site and residing near it, the distance to
industrial and residential areas, and the presence of special facilities near
the site. Adjustment factors for facility age and incident history are also
applied. For each unit/site the adjusted hazard distances are combined to give
a single value, or unit/site score, for comparison with other unit/site scores.
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