Farmers Review Africa Sept/Oct 2018 FRA - September - October 2018 digital 5 | Page 21

requires a different set of solutions
to mitigate fire risk and potential
damage.
Having completed the rational design
and installation for these clients, ASP
Fire also had to meet the challenge
of installation in existing, functioning
structures. “This raises issues
of timing and cost,” Van Niekerk
stresses.
“We can’t always work safely in an
operational facility, so certain areas
need to be shut down for one month
a year, when we can physically
undertake the installation. This is
usually in March or April, after the
harvest and processing of around 50
t to 100 t of seed a day.”
Working with clients to determine the
safest and most cost-effective timing
means finding that unique window of
opportunity where the plant can be
easily and cost-effectively shut down
for maintenance and the installation of
fire-suppression systems.
Fires in solvent-extraction plants can
be managed by means of ventilation,
where the concentration of flammable
vapours is never allowed to reach the
point of combustibility. This requires
forcing air into the environment to
prevent build-up of flammable vapours
below hexane’s lower explosive limit
(LEL), as concentrations under the LEL
are too lean to burn.
In an open structure, there is no
vapour build-up, as this is vented to
atmosphere. In an enclosed structure,
however, solvent vapours are heavier
than air, and can accumulate on
the ground, building up to the LEL.
All that is required for a potential
catastrophe is an ignition source.
To reduce this risk, ASP Fire uses
flammable-vapour detection systems,
flame-detection systems and
sprinklers, noting that entry is difficult
in solvent plants, and also that these
are largely automated, which means
the risk to human lives is greatly reduced.
“The key risk is a hexane leak and
resultant miscella, which is the volatile
mix of the oil and solvent,” van Niekerk
points out. To protect equipment,
high-velocity foam-spray systems are
installed. The steel structure itself is
protected by a foam-sprinkler system.
If there is a spill from a ruptured
vessel that starts to burn a layer of the
spillage on the floor, this can then be
enveloped in foam.
All of these risk-mitigation systems
from ASP Fire comply with the
strict NFPA 36 standard for solvent
extraction plants, which provides
stringent guidelines for fire suppression
and aversion. Compliance is vital for
saving lives, reducing the costs of fire
damage and protecting equipment and
buildings from major damage.
Van Niekerk points out that one of
To protect equipment,
high-velocity foam-spray
systems are installed.The steel
structure itself is protected by
a foam-sprinkler system.
the biggest risks in industries that
use solvents such as hexane is the
so-called BLEVE phenomenon, an
acronym for Boiling Expanding Liquid
Vapour Explosion. A hexane tanker
could be up to 42 m3 in size, so an
incident such as brake failure can
quickly turn into a tanker fire.
“These travelling tankers usually carry
dry chemical powder extinguishers, but
these are ineffective in putting out tyre
fires. Here the biggest concern is the
vessel itself starting to heat up. The
danger is that the liquid reaches the
point where it’s below the level of the
fire, effectively creating super-heated
gas,” van Niekerk elaborates.
The vent on the tanker doesn’t allow
for sufficiently fast ventilation, which
means it heats up quicker than it is
able to evaporate. The tanker then
experiences a mechanical rupture, and
a resultant expanding vapour cloud
that ignites.
The ensuing fireball is calculated to
be 450 times the size of the liquid,
which means that a 45 m3 tanker
equates to a 250 m fireball, and
massive heat radiation as a result.
“One of the models we created
shows that the lethal radius is 360
m from the tanker.Anything closer,
and fatalities result. Even further out,
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