Safety in maintenance process, By B C Das
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Safety in maintenance process, By B C Das

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Maintenance Process provides the guidelines for the long-term aspect of system maintenance in steel industry, Safety Awareness, It is sharing of knowledge. By Bimal Chandra Das, Rtd. AGM (Safety), ...

Maintenance Process provides the guidelines for the long-term aspect of system maintenance in steel industry, Safety Awareness, It is sharing of knowledge. By Bimal Chandra Das, Rtd. AGM (Safety), Bokaro Steel Plant,/ Bokaro. Kolkata

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Safety in maintenance process, By B C Das Safety in maintenance process, By B C Das Document Transcript

  • SAFETY IN PROCESS MAINTENANCE (In Steel Industries)The need of maintenance on a plant implies some abnormality and often some increasein hazard. The conduct of maintenance on the plant is likely to introduce its own typicalhazard that might inflict ham to persons on the job or could even damage the plant andequipment. It is today a moral, professional and legal obligation of plant managers toexercise a careful control over every step of maintenance to eliminate possible hazards orto reduce risks therein to acceptable level.The consequence of failure or neglect to exerciseeffective controls are usually gruesome. Statisticsshow that majority of accidents in a process plantoccur during conduct of maintenance for nonadherence to standardised maintenance practices,characteristically maintenance work in a largeprocess plant employees many groups of workers.This needs a strong system for continuous andeffective communication of job instructions andsafety practices with them. As such a safe andtimely maintenance in process plant can beregulated effectively through application ofsystems 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 Page 1 of 6
  • ♦ Proper supervision and safety monitoringThere are experiences of typical accidents during conduct of maintenance on processplant. They predominantly involved entanglement crush of body parts, fall, burn electricshock or flash-over, gassing, asphyxiation, fire, explosion etc. Investigation revealproximate causes to be use of defective tools & tackle, missing safeguards, weak workingplatform lack of jobs knowledge incomplete information, deployment of workers onunauthorised activities poor supervision etc.During conduct of maintenance a person quite frequently align himself in the path ofmovement of the machine. To avoid accidental injury to such person the principal controlcan be adherence to shutdown practice and permit to work system. A comprehensivelyprepared shutdown protocol takes care of preparatory jobs including compliance to safetystandards and norms before the maintenance work on the machine begins. Job details andrelated safety practices are clearly and explicitly mentioned on shutdown protocols. It isyet vital that the machinery on which the worked is to be done is put to a state in whichpossibility of its making any unexpected movement is reduced to practical minimum. Theterm most commonly used for this is locking out meaning thereby to exercise all logicalprecautions to shutdown the machine for maintenance. Depending upon the type ofequipment the energy source to it (hydraulic, pneumatic, electric, steam, mechanicalspring) should be neutralised before actual work begins. The machine is then at zeromechanical 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. Page 2 of 6
  • In another kind of maintenance wok to be done on an item of process plant operation asstated 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 toanother plart of the plant like vessels, tanks, holders etc. Alternately, it is flared toatmosphere. 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 letis cool down prior to depressurisation in order to avoid flash off.Depressurisation should be done as is contemplated in design details or in standardpractices.Cooling : When plant has not cooled down sufficiently prior to depessurisation it shouldbe allowed to cool now to a required level. Extreme care is necessary here since coolinginvolves hazard of vacuum collapse. This can be guarded against by injecting inert gaslike 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 storagetank specially constructed for the purpose. Non hazardous chemical/effluent are allowedto go to storm drain. Liquid chemical invariably leaves behind hazardous residues in theform 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 caresare 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 Page 3 of 6
  • ♦ 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 avessel/tank which contained flammable or toxic substance. Accident associated with entryof person for conducting work inside plant/tank has occurred with depressing regularity inprocess plants. Before a work is started in such area it is an absolute necessity that thevessel/tank be purged and cleaned to an extent that flammable or toxic substance wouldno longer exit inside it . There are several situations which can lead to the existence offlammable, 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 byproper tests that :♦ The space is free from hazardous situation♦ It does not have an oxygen deficient or as oxygen enriched atmosphere Page 4 of 6
  • An oxygen deficient situation occurs when the space is purged with nitrogen/steam andthen not adequately cleaned ventilated and replaced by atmospheric air. Sometimesprocess 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 byleaking 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 burnviolently when ignited.Shut down procedure and permit-to-work systemTo carry out a maintenance job safety timely and effectively on a plant emphasis is givenon 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 lookfor safety at work site and in practices to complete maintenance worked without a mishapand 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. Page 5 of 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. Page 6 of 6