API RP 581 - 3rd Ed.2016 - Add.2-2020 - Risk-Based Inspection Methodology

RISK-BASED INSPECTION METHODOLOGY, PART 3—CONSEQUENCE OF FAILURE METHODOLOGY 3-123
5.14 Tables
Table 5.1—Event Outcomes for Level 2 Consequence Analysis
Event
Outcome
Pool fires
[10], [17],
[18], [19],
[21], [22],
[24]
Jet fires
[17], [18],
[20]
Fireballs
[17], [18],
[20]
Flash fires
[6], [17], [18]
Vapor cloud
explosions
[5], [6], [7],
[17], [18],
[21], [22], [4]
BLEVEs
[17], [18],
[26]
Physical
explosions
[17], [18],
[36], [30]
Toxic
releases
Description
Occur as a result of immediate
ignition of a flammable liquid from
a pressurized process vessel or
pipe that leaks or ruptures.
Occur as a result of immediate
ignition of a flammable vapor or
two-phase jet release from a
pressurized process vessel or
pipe that develops a hole.
Occur as result of the immediate
ignition of a flammable,
superheated liquid/vapor
released due to a vessel or pipe
rupture. Fireballs always occur in
combination with a physical
explosion or a BLEVE.
Occur as a result of a delayed
ignition of a vapor cloud. The
source of the vapor cloud could
either be from a vapor or twophase
jet release or evaporation
off the surface of an un-ignited
liquid flammable pool.
Occur upon rupture of a vessel
containing a superheated but
pressurized liquid that flashes to
vapor upon release to
atmosphere
Occur upon rupture of a vessel
containing a pressurized
flammable or nonflammable
vapor
Occurs upon release of toxic fluid
to the atmosphere through a hole
or due to a rupture
General Procedure
1. Determine pool fire size
2. Calculate burning rate
3. Calculate flame length and tilt
4. Determine radiant energy emitted
5. Determine energy received at distant points (need view factor
and atmospheric transmissivity)
6. Calculate safe distance
1. Calculate flame length
2. Determine radiant energy emitted
3. Determine energy received at distant points (need view factor
and atmospheric transmissivity)
4. Calculate safe distance
1. Determine available flammable mass
2. Determine fireball diameter, height and duration
3. Determine radiant energy emitted
4. Determine energy received at distant points (need view factor
and atmospheric transmissivity)
5. Calculate safe distance
1. Determine if cloud source is continuous (plume) or
instantaneous (puff)
2. Utilize cloud dispersion model to determine the grade level
area of flammable material (greater than LFL) that is in the
source cloud
1. Determine if cloud source is continuous (plume) or
instantaneous (puff)
2. Utilize cloud dispersion model to determine the amount of
flammable material (between LFL and UFL) that is in the
source cloud
3. Determine equivalent amount of TNT
4. Calculate overpressure as a function of distance
5. Calculate safe distance
1. Determine equivalent amount of TNT that is a function of the
storage pressure and the amount of liquid that flashes to vapor
upon release
2. Calculate overpressure as a function of distance
3. Calculate safe distance
1. Determine equivalent amount of TNT that is a function of the
storage pressure and volume of vapor
2. Calculate overpressure as a function of distance
3. Calculate safe distance
1. Determine if cloud source is continuous (plume) or
instantaneous (puff)
2. Utilize cloud dispersion model to determine the portion of the
cloud at grade level that exceeds the toxic limit (concentration
and duration) of the fluid