Hydrocarbon Processing - November 2022 - 64

Plant Safety and Environment
* Intentional or unintentional
process emissions to atmosphere
from liquid sulfur storage areas
(e.g., pit, tank, loading)
process fluid releases over the past 30 yr, or
roughly one serious process fluid release
incident every year. These cases include:
* Six gas release incidents involving
types of process-fluid-release failures.
Regarding incident investigations for
process fluid releases, the type of release
(H2
Despite the constant improvements in design, operation
and understanding of SRUs, physical and mechanical failures
continue to occur frequently, causing loss of processing
and profits, and leading to significant safety incidents.
° Emissions from storage areas
are often allowed to vent directly
to atmosphere.
° Even if emissions are collected
for processing, these systems
are often unreliable.
° Emission points are sometimes
near or at ground level.
° Operators and transportation
personnel are often not fully
aware of the potential of H2
and SO2
S
concentrations.
* Loss of containment due to fires,
explosions, corrosion or plugging:
Equipment damage or plugging can
result in the secondary impact of
unwanted process fluid release.
* Manual opening of process lines
to atmosphere: Many incidents
are due to improper safety
procedures when opening sample
points or process bleeds.
* Equipment entry during a
turnaround: H2
S, SO2 and sulfur
are often present in the equipment.
Examples of process fluid releases are
shown in FIG. 6.
A review of the author's company's case
files reveals around 30 incidents of serious
H2S deaths or knockdowns
* Six other high-concentration
H2
or knockdowns
* Ten shelter-in-place incidents
(large SO2
or H2S releases)
* Four liquid sulfur injuries or deaths
* Five significant liquid sulfur spills.
Because of the relative scarcity of H2
S
and liquid-sulfur-related deaths and injuries
in the author's company's files, a
review of online records from the Occupational
Safety and Health Association
(OSHA) for these two categories was
undertaken to better understand the frequency
of these events. While this review
only shows U.S. incidents, and only for
the period of OSHA records (starting
in 1984), it still provides a good appreciation
of the prevalence of these types of
cases. This data is detailed below:
* OSHA-recorded H2
S deaths
in the U.S. (all industries)7
° 1984-1989: 42 deaths (7/yr)
° 1990-1999: 70 deaths (7/yr)
° 2000-2009: 48 deaths (4.8/yr)
° 2010-2021: 43 deaths (3.6/yr)
° Total U.S. H2
S deaths in amine,
sour water stripping, SRU
operations: Eight deaths
° Total U.S. H2
S deaths in liquid
sulfur transportation: Eight deaths
° Total U.S. liquid sulfur injuries or
deaths: Six cases involving nine
injuries and one death.
FIG. 6. Examples of process fluid releases.
The 16 SRU-related H2
equate to around one H2
S deaths
S-related death
FIG. 7. Examples of SRU explosions.
64 NOVEMBER 2022 | HydrocarbonProcessing.com
every 2 yr in the sulfur industry, while
the liquid sulfur cases equate to around
one injury or death every 3 yr. Overall, although
process-fluid-related incidents remain
relatively rare in the SRU industry,
they are still occurring and do have significant
consequences. This data shows that
the industry still requires improvements
in design and procedures to avoid these
Explosions. Explosions in the sulfur recovery
industry (FIG. 7) typically fall into
four categories:
1. H2
S explosions-H2
S lower
explosive limit (LEL) 3.2%,
the lowest possible LEL over
the full range of normal SRU
temperatures: Most likely
in liquid sulfur storage and
transportation vessels due to
H2
S release from liquid sulfur8
2. Sulfur dust explosions
(sulfur dust LEL is 35 mg/l):
Most likely in solid sulfur forming,
storage and transportation vessels
S releases not involving deaths
S, SO2 or liquid sulfur) is usually obvious.
The determination of
the root cause(s) usually comes
down to a combination of design
reviews, equipment walkthroughs,
historical data reviews
and personnel interviews to
determine if the release was the
fault of design or due to operational
or personnel procedures.
Regarding prevention of future process
S and SO2
fluid releases, the presence of IDLH levels
of H2
within the normal process
gas flow path is well known in the industry.
For this reason, proper design, safeguarding
and instrumentation of SRUs are commonplace,
and regular detailed hazard and
operability studies (HAZOPs) are recommended
to ensure that the design meets
current standards; a full discussion of
recommended safeguarding is outside the
scope of this article. However, most process
gas or fluid injuries and deaths in the
author's company's investigations and in
OSHA records are not related to mechanical
failures, but, instead, to poor understanding
by plant personnel of the potential
concentrations of dangerous process
fluids at all locations-and also to improper
procedures involved with inspecting,
handling and opening various process
locations, especially in the liquid sulfur
collection, storage and transportation areas,
as evidenced by the high number of
H2
S deaths in the transportation sector.
Improved training for personnel involved
in these areas, along with more consistent
design and procedural safeguards, would
go a long way toward reducing the risk of
serious process-fluid-release incidents.
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