Hi everyone, I would like to share some questions/notes, I
made during a HAZOP (Hazard Operability) safety study for a 25 tonne storage
tank and its distribution system, handling toxic materials at a facility.
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Generic Chemical Storage Tank |
Questions:
General System:
1.
Is a direct liquid feeding system safer than one
with multiple smaller day tanks?
·
Safer for direct feeding as there is less
instruments, leak paths & point of failures
·
BUT not good for production as day tanks provide
buffer if a transfer pump shuts down
·
Direct feeds may have higher flowrates (unsafer
if it leaks) – thus day tanks are preferred
2.
Is there
any use of different material of construction, valves, seats or seals out of
specifications in the distribution system? - This can be a source of
leakages and fugitive emissions
3.
Is there a common vent line shared between the
multiple day storage tanks? Are these tanks sealed for overflow of liquid into
the vapour line?
·
Vent lines equalises pressures & allow for
expansion of vapours
·
A failure of overfilling liquid in one tank may
trigger level alarms in all the day storage tanks - when it could be instrument
fault or human error in one tank, Thus difficult to troubleshoot
4.
Are there any safeguards for improper
connections of vapour return line onto tanker? i.e. CCTV, 2nd
signature checklist, labelling, etc.
Equipment:
5.
Is there an issue for pumping air into the tank?
Will this effect quality of the chemical
storage & used in the facility?
6.
Can the transfer pump can run dry? As magnets
can burn out, overheat and be damaged. Wil the operator have to break into line?
Can a seal-less pump be used instead? As it is self-priming, thus prevents
restarts
7.
Can a spill back line (return) for the pump be
used to mix with potentially frozen fluids?
8.
What is the procedure for changing the filters
of the pump? Is there decontamination process? Is splashing a possibility? How is
releases to drain or ground water prevented?
9.
For the gas scrubber/extractor – Is the
activated carbon the right grade/type? Can a sign be put up to inform operators?
Scrubbers usually catch fire with ketones – thus confirm suitability with toxic
material
10.
Is there a possibility for obstruction in the exhaust
outlet of an extraction fan? i.e. a birds nest.
Safety Systems
11.
Can the tanks relief valves/Burst discs be
installed incorrectly backwards?
12.
Is foaming or bubbling a possibility in the burst
disc? Check ullage/head space of tank for foaming allowance
13.
Does temperature effect the operation of the
tank relief valve and does the room need temperature control?
·
Higher temperatures, thus vapour generation &
more vapour flow through relief valve
·
Low temperatures, more crystallisation & solidifying
may take place
·
Consider using adhesive surface temperature
indicator, which changes colour (typically used in a fish tank)
14.
What is the sizing basis for the vacuum relief
valves? Is there any potential for chemical reactions that remove gases from
head space of the tank?
·
Due to corrosion of interior of a steel vessel
·
Newly cleaned steel with chemicals can remove
oxygen
·
E.g. Ammonia reacting with chlorine to form
ammonia chloride
15.
Is there potential for blockages in the tank and
distribution system?
· Material
can polymerise, crystallise, condense or solidify
·
Monomers can escape a tank free of inhibitors
·
Waxes & viscous high boiling point materials
can solidify
·
Dust accumulation
·
Water vapours can condense to form liquid seals
in low points or freeze in winter!
·
Is there any
16.
How are leaks controlled in flanges of transfer
pipework? Can you put portable sniffers
into flange guards to detect leaks, rather than detecting in the local
air/atmosphere
·
Can you use shrink wrap around flanges too, BUT
may not be compatible – may melt if leaks
·
Still needs to remove containment toxic materials
from flange guard (secondary) as also may lead to release
·
Can you
plot a table to justify hiring one person for inspections/plant walk throughs –
account for the following variables…
i.
Size of pipework (diameter in inches NB)
ii.
Proximity of release area of people
iii.
Activity in area – where 0 = heavy work and 1 =
no work, i.e.. 0.2 = walkthrough
iv.
Ventilation – where 0 = none, 1 – full, i.e. 0.2
for doors, etc.
v.
Frequency to exposure
vi.
Maybe hire someone for 2 months of the year for
regular emissions testing
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Hope you have enjoyed reading this
Chiraq