MB Petroelum third party fatality

1
Safety Alert
No. 14 Oct 98

Committed to Safety
Tank Cleaning
Background A fatal incident occurred recently in
a refinery in The Netherlands during a tank
cleaning operation with water. It was followed by
a second and apparently similar incident in
another location (this time fortunately without
fatal consequences). In both cases
? a person was cleaning a small tank, from the
top, using water. ?? a manhole on
the roof was opened and evidently a significant
quantity of air entered the tank.
? an explosion occurred, strong enough to blow
away the roof of the tank some 50 to100 meters
away.
Causes of the incidents A detailed investigation
on the reasons of the two incidents is presently
in progress. However, the following hazards
linked to this kind of operation may have been
present in these incidents. ????????????????
Air entering a tank can create an explosive
mixture with the gas present. ? Hydro jetting
of a tank can create static electricity which may
discharge and subsequently ignite an
explosive gas mixture. Learning Points and
Action to Prevent Recurrence ? Operating
procedures for tank cleaning shall always be
implemented as per approved guidelines/
standards and PDO approved operation procedures
(Preparation of tanks and vessels for internal
work on fixed tanks (OP12), and PDO standard
TOM/03/0000/301 for the cleaning and gas freeing
of mobile tanks). ? Explosive/flammable mixtures
may develop typically during the emptying of
tanks due to air entering and mixing with the
residual gases. On no account should confined
space be entered if the explosimeter reading is
equal to or greater than 10 LEL. ???????????????
? The scope of applying inert gas to atmospheric
pressure type storage tanks is limited. Each
application will
require special study and may require particular
precaution. ???????????????? Electrostatic
charges coming from water jetting are a source of
ignition with enough energy to
ignite a flammable gas/air mixture. To
prevent accumulation of electrostatic charges on
bodies such as tank shell, hoses and nozzles
etc. it should be ensured that they are
electrically conductive and properly bonded and
earthed. It is essential that an
inspection and test of all bonding and earthing
connections is made before any tank
cleaning takes place.