The document discusses safety procedures for maintenance work in steel plant processes. It emphasizes establishing standardized maintenance practices, permit-to-work systems, and shutdown protocols to isolate equipment from energy sources. These controls are needed as maintenance introduces hazards and most accidents occur due to non-compliance with safety practices. Proper isolation, cleaning, testing for hazards, and control of large workforces are essential for safe maintenance of chemical equipment and preventing accidents like burns, asphyxiation or explosions.

1. SAFETY IN PROCESS MAINTENANCE
(In Steel Industries)
The need of maintenance on a plant implies some abnormality and often some increase
in hazard. The conduct of maintenance on the plant is likely to introduce its own typical
hazard that might inflict ham to persons on the job or could even damage the plant and
equipment. It is today a moral, professional and legal obligation of plant managers to
exercise a careful control over every step of maintenance to eliminate possible hazards or
to reduce risks therein to acceptable level.
The consequence of failure or neglect to exercise
effective controls are usually gruesome. Statistics
show that majority of accidents in a process plant
occur during conduct of maintenance for non
adherence to standardised maintenance practices,
characteristically maintenance work in a large
process plant employees many groups of workers.
This needs a strong system for continuous and
effective communication of job instructions and
safety practices with them. As such a safe and
timely maintenance in process plant can be
regulated effectively through application of
systems mainly like:-
(a) Approved shut down procedure and
(b) Standard permit to work system.
The basic elements of overall safe maintenance can be:-
♦ Standardised maintenance procedure for major maintenance activities.
♦ Documentation of work practices and equipments involved
♦ Permit to work and handing over system
♦ System for dealing with large workforce employed through contractors
♦ Job specific training to workers
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2. ♦ Proper supervision and safety monitoring
There are experiences of typical accidents during conduct of maintenance on process
plant. They predominantly involved entanglement crush of body parts, fall, burn electric
shock or flash-over, gassing, asphyxiation, fire, explosion etc. Investigation reveal
proximate causes to be use of defective tools & tackle, missing safeguards, weak working
platform lack of jobs knowledge incomplete information, deployment of workers on
unauthorised activities poor supervision etc.
During conduct of maintenance a person quite frequently align himself in the path of
movement of the machine. To avoid accidental injury to such person the principal control
can be adherence to shutdown practice and permit to work system. A comprehensively
prepared shutdown protocol takes care of preparatory jobs including compliance to safety
standards and norms before the maintenance work on the machine begins. Job details and
related safety practices are clearly and explicitly mentioned on shutdown protocols. It is
yet vital that the machinery on which the worked is to be done is put to a state in which
possibility of its making any unexpected movement is reduced to practical minimum. The
term most commonly used for this is locking out meaning thereby to exercise all logical
precautions to shutdown the machine for maintenance. Depending upon the type of
equipment the energy source to it (hydraulic, pneumatic, electric, steam, mechanical
spring) should be neutralised before actual work begins. The machine is then at zero
mechanical state and affects maximum protection against unexpected machine movement.
The zero mechanical state of machine ensures:
 Every power source that can produce a machine member to move is isolated
 Air/oil line shutoff valve blocks pressure from power source. Pressure to machine
is educed by venting air to atmosphere or draining oil to another container.
 All accumulators or air surge tanks are reduced to atmospheric state.
 Mechanical potential energy of all members of machine is at its lowest potential
valve and that opening of pipes, tubes, hoses or actuation of any valve will not
produce a movement to cause injury.
 The kinetic energy of the machine members is at its lowest practical value.
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3. In another kind of maintenance wok to be done on an item of process plant operation as
stated under are significant .These however require a great deal of job knowledge,
experience, involvement and safety awareness.
Depressurisation: In this process flammable and toxic gases are preferably transferred to
another plart of the plant like vessels, tanks, holders etc. Alternately, it is flared to
atmosphere. Inert gas is vented to atmosphere through a pipe or stack.
If the plant contains liquid chemical heated above its boiling point (BP of benzene-80.1,
NH3-335 c naphtha 30 c toluene 110 c, xylene 139 c) under pressure it is desirable to let
is cool down prior to depressurisation in order to avoid flash off.
Depressurisation should be done as is contemplated in design details or in standard
practices.
Cooling : When plant has not cooled down sufficiently prior to depessurisation it should
be allowed to cool now to a required level. Extreme care is necessary here since cooling
involves hazard of vacuum collapse. This can be guarded against by injecting inert gas
like nitrogen to maintain the internal pressure at atmospheric pressure.
Emptying: Once the plant has been isolated removal of its contents is taken up.
Hazardous liquid chemical is usually pumped to another part of the plant or to storage
tank specially constructed for the purpose. Non hazardous chemical/effluent are allowed
to go to storm drain. Liquid chemical invariably leaves behind hazardous residues in the
form of deposits or studies. They may be highly flammable or toxic and sometimes both.
It is generally the practice to remove them by cleaning with steam, where following cares
are recommended:
♦ Steam should not create excess pressure in the plant/tank.
♦ Condensate taking with it the residues should be drained off from lowest possible
point.
♦ Temperature rise in plant/tank should be sufficient to ensure removal of residues
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4. ♦ The process of cleaning should be monitored by content of residue in the
condensate
♦ Steam hose and tank should be bonded together and well earthed to minimise risk
of static electricity.
♦ High superheat steam should be avoided as it can damage equipment
♦ Effect of steaming can be one thermal expansion of the tank and therefore a stress
on associated pipelines.
Cleaning : It is necessary in a maintenance work that a person is allowed to enter into a
vessel/tank which contained flammable or toxic substance. Accident associated with entry
of person for conducting work inside plant/tank has occurred with depressing regularity in
process plants. Before a work is started in such area it is an absolute necessity that the
vessel/tank be purged and cleaned to an extent that flammable or toxic substance would
no longer exit inside it . There are several situations which can lead to the existence of
flammable, or toxic substances in it.
• Flammable/toxic substance has not been completely removed.
• Flammable/toxic residues that remain in the vessel evaporate.
• Residues are trapped in construction members in the vessel/tank
• Solid residues vaporise when heat is applied or welding, gas cutting work on body of
item is carried on
• Flammable or toxic gas build up in vessel/tank through the isolations which may not
be leak light (use of single isolation is seldom reliable)
• Flammable /explosive gas is liberated by chemical reactions, e.g. action of water on
steel tank can generate hydrogen.
Before a person is allowed to enter into such vessel/tank it should be ascertained by
proper tests that :
♦ The space is free from hazardous situation
♦ It does not have an oxygen deficient or as oxygen enriched atmosphere
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5. An oxygen deficient situation occurs when the space is purged with nitrogen/steam and
then not adequately cleaned ventilated and replaced by atmospheric air. Sometimes
process occurring inside the tank/vessel consumes oxygen .
• Combustion of flammable substances such as in welding or other hot work
• Oxygen level may stay dangerously low after a fire is out because the oxygen is
replaced by products of combustion.
• Some paints absorb oxygen from atmospheric air when it is applied on wall
suffice.
An oxygen rich atmosphere is caused by leaking oxygen cylinders in a storage or by
leaking oxygen gasoline valve installed inside a room. Such situation are rarely possible.
On occurrence this can enhance the flammability of air clothing and have to burn
violently when ignited.
Shut down procedure and permit-to-work system
To carry out a maintenance job safety timely and effectively on a plant emphasis is given
on observance of formal shutdown procedure and standard permit to work system.
Statutory provisions under different acts and rules have also given stress on this to look
for safety at work site and in practices to complete maintenance worked without a mishap
and delay.
More explicitly the objectives of shutdown procure and permit to work system are:
• It provides continuous control on the work
• The person responsible for overall control of work and its execution is identified
• The person responsible for operation of the plant is aware of the work.
• The agencies to be deputed on work are selected and job related and safety related
communications with them are established and maintained.
• The work is properly defined
• The isolation and locking out are properly effected
• Proper tools and equipments are available and arrangements are in place to
support precautions.
• A formal undertaking is reached between operation and maintenance group before
start of maintenance work.
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6. • There is procedure covering situation where the work extends beyond a single
shift
• There is procedure covering situation where the worked is to be suspended on
emergency
• There is record showing that nature of work and the safety precautions that are
necessary were checked by appropriate authority.
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