6.6 Maintenance Flashcards
If equipment has to run during a maintenance operation and this presents risks, appropriate controls should be introduced to reduce the risk, for example: 3
provision of temporary guards limited movement controls crawl speed operated by hold-to-run controls.
A SSW is required when
hazards cannot be eliminated and a degree of risk remains after technical control measures are introduced.
The systematic analysis of a task may be undertaken in various ways: 3
A job safety analysis (JSA) may be used to break the task down into its component steps and identify hazards at each stage. A MEEP analysis may be used in conjunction with, or independent to, a JSA and uses the headings materials, equipment, environment or people (MEEP) to prompt consideration of potentially unsafe conditions, and unsafe acts. Other approaches consider what, who, where and how, or the 4 Ps – premises, plant and substances, procedures and people.
A simple SSW may be defined verbally, as a written procedure or become a formal Permit-to-Work (PTW) (discussed later), depending on the level of risk and the needs of the organisation. In all cases the SSW should: 5
Consider the preparations and authorisations necessary before beginning work. Ensure the job sequence is logically and clearly planned. Specify safe methods for undertaking specific activities. Specify safe means of access and egress if relevant. Consider the end of activity tasks such as dismantling and disposal.
In order to install a large item of machinery such as a turbine rotor, it is sometimes necessary to perform adjustments while the rotor is in motion. These adjustments are necessarily undertaken with the rotor in an unguarded condition. Outline the elements of a safe system of work for this activity. 10 marks
The elements of a safe system of work for carrying out the operation described in the question include: the use of experienced workers fully trained in the systems to be adopted, since this is not a task to be carried out by the young or inexperienced the provision and use of a single, one-piece, close fitting overall with no external pockets, together with arrangements to ensure there are no other entanglement hazards present, such as the wearing of jewellery, or long hair the use of temporary guards or the isolation of parts of the machine which are unnecessarily exposed where practicable the use of jigs to ensure workers’ hands are distanced from the unguarded rotor the provision of a ‘stand by’ man in direct contact with the person carrying out the work, with means of immediate communication such as telephone or radio to ensure an emergency response, should the need arise the provision, close at hand, of emergency stop or braking arrangements the use of an inching device to minimise the free rotation period, or using the slowest speed possible consistent with the task the provision of non-stroboscopic lighting the introduction of a permit to work to formalise the establishment of the safe system of work the erection of barriers and signs to prevent the close approach of non-involved personnel.
The essential features of permit-to-work systems are: 5
Clear identification of persons responsible for authorising particular jobs (and any limits to their authority) and persons responsible for specifying necessary precautions. Clear identification of the types of hazardous work. Clear and standardised identification of tasks, risk assessments, permitted task duration and supplemental or simultaneous activity and control measures.to-w Training and instruction in the issue, use and closure of permits. Monitoring and auditing to ensure that the system works as intended.
The basic process involves: Issue by a competent issuing authority, setting the parameters of the permit and confirming that precautions are in place. Acceptance by a competent worker (performing authority), confirming understanding of the work to be done, hazards involved and corresponding precautions. Handback of the PTW, by the performing authority, confirming that the work has been completed to plan. Cancellation of the PTW by the issuing authority confirming the work has been tested and the work area returned to normal use. Additional procedures are required for
extension of agreed time limits if necessary, and for managing shift handovers.
Isolation (and energy dissipation) of external energy sources may require management of the following: 5
Mechanical power transmission: by isolating clutches, by removal of drive belts or chains, or shaft sections. Scotching may also be used. Electrical power: by isolating switches by removal of fuses, or by removal of plugs from sockets. Earthing or short-circuiting may also be needed. Hydraulic or pneumatic power: by isolating valves, by electrical isolation of hydraulic pumps, or by disconnection from pneumatic mains. Open venting to atmosphere may also be required. Services: isolation of water, steam, gas or fuel supplies. Draining or venting may also be needed. Process and material supplies: isolation of process lines and line blinding or blanking off. Draining or venting may also be needed.
The following sources of residual energy storage or material internal to the machine or equipment may also need to be dealt with, as follows. 6
Mechanical power: allow flywheels or high speed rotating parts, such as centrifuge bowls, to run down, and to minimize the potential energy of other parts. Electrical power: discharge of capacitors, disconnection of stand-by batteries, or earthing and short-circuiting of high voltage circuits. Hydraulic power: discharge of accumulators, or relaxation of pressurized pipe-work. Pneumatic power: discharge of air pressure throughout the system (except where used for hold-up. Note: where hydraulic or pneumatic hold-up devices have been provided for mechanical parts, those selected should be of high reliability. Services: residual steam, gas or fuel may need to be vented, purged or drained. Process and material supplies: emptying, venting, purging, draining and/or cleaning may be required before entry.
