This document discusses pyrophoric ignition hazards in refinery operations. It defines pyrophorics as materials that can ignite without an external ignition source when exposed to air. Pyrophoric iron sulfide can form under certain conditions and ignite residual hydrocarbons. Examples are given where pyrophoric reactions have occurred in tanks, vessels, reactors, and separators, sometimes causing fires or explosions. Mitigation methods include chemical neutralization of deposits before opening equipment and maintaining inert atmospheres.

1. © 2010 Chevron
Pyrophoric Ignition Hazards in
Typical Refinery Operations
CAER Safety Summit Meeting
December 2010.
Doug Jeffries
Chief Fire Protection Engineer

2. © 2010 Chevron
Agenda
Definitions and chemistry of pyrophorics
Conditions required to form pyrophoric iron sulfide
Where pyrophorics have been known to form in refinery equipment
Possible methods to mitigate and prevent pyrophoric related incidents
A couple example pyrophoric related incidents
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Definitions
A pyrophoric material is a liquid or solid that, even in small quantities and
without an external ignition source, can ignite within 5 minutes after
coming in contact with air1
In oil and petrochemical industry, this only partially defines the concern.
We also need to be concerned with the fact the pyrophoric material can
create heat which can ignite residual hydrocarbons associated with the
equipment containing the pyrophoric material.
Example pyrophoric materials include alkali metals and many
organometallic compounds such as alkylmagnesiums, alkylzincs, and
of course pyrophoric iron sulfide. Nickle carbonyl in some catalysts
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Chemistry of Pyrophorics
Pyrophoric compound + oxygen (typically air) Oxide of the
compound + heat
Sometimes with several intermediate reaction steps
Can be very reactive or very slow to react
Can vary with conditions, humidity, temperature, particle size, degree of
disbursement in air, etc.
Bottom line: pyrophorics can be a very elusive and tricky animal to
recognize and capture until it bites you
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Conditions required to form pyrophoric iron sulfide
H2S concentration > 1% (can form at lower concentrations but
typically not in concentrations that are a concern)
Iron scale or rust (FeS)
Less than a 1:1 ratio of oxygen to H2S (some oxygen is required to
form the rust but if insufficient oxygen is present the reaction with H2S
cannot go to completion)
Fe2O3 + 3H2S = 2FeS + 3H2O + S
4FeS + 3O2 = 2Fe2O3 + 4S + heat
4FeS + 7O2 = 2Fe2O3 + 4SO2 + heat
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Where pyrophorics have been known to form in refinery
equipment
Crude oil tanks
Asphalt tanks
Sour water tanks
Vessels in sour service such as coke drums, distillation columns, inlet
separators, pig receiver / launchers
Reactors
API Separators
Marine tankers and barges
Portable tanks and tote bins
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Pyrophorics and the Fire Triangle
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FUEL
IGNITIONOXYGEN

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Example 1
Marine tanker cargo hold.
Cargo was light crude with low, sufficient vapors to reduce oxygen
levels to near zero
High humidity accelerated rust and formation of pyrophoric iron
sulfide
As crude cargo was off loaded, the normal inerting with engine
exhaust was halted
Air was allowed to enter causing the pyrophoric iron sulfide to react,
heat up, and ignite
Fortunately, the vapor space was relatively small so the damages
were slight and there were no injuries
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Example 2
Filter cake deposits ignite.
Powdered filter cake is added to a mix tank to assist filtration after
mixing
Powder accumulates in the vapor space of the tank, particularly near
the baffles
Reaction begins to occur but is disrupted when product and more
filter cake dust covers the deposits
Vibration from turning on the tank mixers or disturbance while
cleaning the tank exposes the unreacted layers in the deposits
The reaction generates heat igniting vapors in the tank
The tank is severely damaged but thankfully there were no injuries
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Example 3
Reactor catalyst ignites in drums.
Reactor is normally flooded with water prior to dumping catalyst
In a trial to recover more precious metal and reuse the catalyst, it is
decided to dry dump
Process stream contains hydrogen sulfide and nickle carbonyl and
possibly other pyrophoric compounds are formed in the catalyst
Reactor is purged with nitrogen while dumping catalyst and
removing internals
Upon exposure to air catalyst heats up, igniting residual hydrocarbon
in the catalyst
Fortunately, drums are moved away from the reactor so no damage
and no injuries
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Example 4
Sour water tank roof blown off.
Sour water is high in H2S and is a wet environment
Odor complaints cause operators to alter the tank vent and
pressure / vacuum valve
Normal ventilation of the tank vapor space is changed resulting in
formation of pyrophoric iron sulfide
When the tank vent and P/V valve are returned to normal service,
oxygen is allowed to enter
Pyrophoric iron sulfide reaction occurs, sufficient heat is generated
to ignite the vapor space blowing the roof off the tank
A similar incident occurred when the tank was opened for cleaning
and inspection
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Example 5
API Separator explosion.
An API Separator in an upstream producing facility is in operation in
a sour producing area
The separator is gas blanketed to prevent oxygen from getting inside
Pyrophoric iron sulfide forms inside the separator
The separator is taken out of service for maintenance
No washing or chemical neutralization is performed prior to opening
the separator
Air enters, a pyrophoric reaction takes place, igniting residual
hydrocarbon inside the separator
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Example 6
Hot oil tank fire.
A refinery has a hot oil tank and hot oil system for heating process
streams and storage tanks
The synthetic hot oil compound is replaced with medium cycle oil
from the catalytic cracker (which happens to contain H2S and a high
level of particulates)
The particulates accumulate in the horizontal hot oil tank, mandating
a clean out.
The oil is drained and the decision is made to put a man inside to
soften the deposits with diesel
The manway and vent are opened, the man enters
Air sweeping across the top of the tank produces a pyrophoric
reaction which heats and ignites hydrocarbon
The man inside the tank receive fatal burns
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Mitigation methods
Most effective method is chemical neutralization before opening the
equipment; potassium permanganate solution (typically around a 1%
solution, circulate and check for color)
Keeping the deposits and scale wet until it can be safely removed to
a remote area and allowed to dry
Maintain a constant air ventilation to ensure there is plenty of oxygen
to allow the reaction to go to completion, preventing the formation of
the pyrophoric intermediates
Replace components that contain sulfur compounds
Use nitrogen or other inert gases to keep oxygen out (obviously
difficult and adds hazards of its own)
Quickly move scale and potential pyrophoric deposits to a remote
area and monitor in case ignition does occur
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