This report will be in two parts, in part one, a risk assessment will be carried on a pneumatic conveying system for fire and explosion hazards in the process while in part two a maintenance schedule will be carried out on the whole plant system, identifying maintenance procedures which are critical to the safe operation of the plant.
Health and safety legislation relevant to the risk assessment and maintenance will be discussed.
Part 1 (Risk Assessment)
BACKGROUND (PNEUMATIC CONVEYING SYSTEM)
This conveying system conveys high velocity substances incessantly where compressed air is readily available. The system is used for conveying Pharmaceutical powder pharmex at low density over a short medium distance. A pneumatic conveying system may transport solids up to approximately 50mm size and the powder or solid must be dry, with no more than 20% moisture. Since pneumatic systems are completely enclosed, product contamination, material loss and dust emission are reduced or eliminated.
The pipeline and blow tank are pressure rated to above 15 barg.
The filter housing and receiving vessel are pressure rated to 0.3 barg.Risk Assessment Process
Risk: This is the likelihood that a severity will occur, it's also the product of probability of a failure event occurring and the undesired consequence.
Risk = Probability of failure x Undesired consequence
Hazard: This is the potential of a substance, activity or process to cause harm (Hughes and Ferrett 2003). Anything that is not properly handled could be term hazard.HSE Approach to Risk Assessment
Risk assessment is simply a careful examination of what could cause harm to people in a workplace or environment, so that precautions available will be weighed if enough, or more work should be done to prevent harm (hse.gov.uk 2010).Assessing the Risk
- Identifying the hazards: A thorough walk around and asking right question will help point out hazards which could pose a serious danger to both people and equipments.
- Consider persons at risk: Deciding who might be harm will help identify the best way to manage the risk.
- Evaluating the risk and deciding on precautions: The purpose of risk assessment is to reduce all residual risk to As Low As its Reasonably Practicable (ALARP). Basic risk assessment (identifying the risk), quantitative risk assessment, and qualitative risk assessment are used in evaluating the risk.
- Reviewing assessment and revising if necessary: Risks and its controls should be reviewed periodically and implementing controls where appropriate in case of changes in conditions such as new machinery, receipt of new chemicals.
Quantitative risk assessment: Measures the risk by relating the probability of the risk occurring to the possible severity of the outcome and then giving the risk a numerical value. The likelihood depends on the control measures of the place, while the severity depends on magnitude of hazard (Hughes and Ferrett 2003).
Qualitative risk assessment: This is based on personal judgement and is normally defined as high, medium or low. This kind of assessment is usually satisfactory since the definition whether high, medium or low determines the time frame in which further action is to be taken. High risk situations need to be addressed in days, medium risk in weeks and low risks in months (Hughes and Ferrett 2003).
Record findings: A formal reporting procedure needs to be implemented and incorporated into the current risk assessment reporting procedures. The significant hazards and conclusions need to be recorded for the assessment to be suitable and sufficient. It should also include existing control measures and their effectiveness.
PNEUMATIC CONVEYING, FIRE AND EXPLOSION HAZARDS
In considering the fire triangle, ignition source, fuel and air will favour fire explosion. In the pneumatic conveying system, the pharmaceutical powder is the fuel, air in the system is the oxidant and the basic for safety will be the removal of the ignition source. The ignition source can be static charges, sparks from parts in motion, hot surfaces caused by powder motion. There should be an extinguishing precaution, such as mounting the Bicarbonate soda powder on the filter housing to minimise the risk if there is an explosion. Fire and explosion risk should be assessed in order to minimise the possibility of it occurring by ensuring that the elements of the fire triangle are shielded from each other so that they do not come in contact.
Hazards associated with the Pneumatic Conveying System
Filter housing and storage hopper
This has to be treated as on vessel, the receiving vessel has to be strong enough to take the weight of powder fed to it. The filter housing and the receiving vessel are pressure rated at 0.3 barg and cannot withstand the maximum explosion pressure of 10 barg, so a suppression unit should be fitted with a differential pressure transducer which helps to curb the explosion should it occur. The pressure transducer activates the fire extinguisher in case of pressure rise thereby spraying bicarbonate soda powder in the event of an explosion.The pipe line
The moving powder in the pipeline has a low possibility of igniting as there isn't sufficient time for a spark to transfer energy to the moving powder. The pipeline needs to be inspected for possible corrosion and blockage that can aid in possibility of fire or explosion occurring.Blow tank
The blow tank is capable of withstanding the explosion. The maximum explosion pressure is 10 barg which is less than blow tank pressure.Compressor
An isolation valve is needed to stop blow back to the compressor in the event of an explosion. Blow back arrestors should be installed to stop the powder from being blown back. To eliminate the possibility of the compressor becoming an igniting source as a result of the engine been too hot, it needs to be installed in a separate room.Nozzle bank
As the full output of the compressor is not needed, the nozzle bank should be fitted to control the flow of air. It consists of series of critical flow orifices which will only allow certain maximum flow of air. The nozzle bank necessitates the varying of air flow rate from no flow to a series of flow rates depending on open valves.Managing the Ignition Source
Mechanical ignition source: Tramp metal in the valves, hot bearings, motors, and badly lubricated equipment can give rise overheating which is a source of ignition. To minimise the probability of the mechanical parts becoming an igniting source, proper lubrication should be done and flushing done to rid of the metal in the pipeline.
Electrical ignition source: Motors, non insulated wires can produce sparks and circuit could overheat hence cause a spark. Proper insulation and special motors are required for use in potentially flammable surroundings.
Static ignition source: Due to the powder and air density differential, adhesive forces due to friction travelling down the pipeline might cause static charges possible of acting as an igniting source. As a remedy, earth bonding of all the systems including the filter bag which should be metal backed so it can be earthed. Tramp metal which acts as isolated conductor thus storing charges should be removed by screening.
Thermal ignition source: Overheating of parts in motion such as bearings, motors and belt could act as a source of ignition. To minimise the likelihood of overheating, the room where the conveying system is housed should be properly ventilated to allow air circulation hence reduce temperatures.
Human ignition source: The area of the plant must be designed as a no smoking zone to ensure or reduce the chances of lighting open flames which can act as a source of ignition and cause explosion. To prevent possible ignition sources that might be caused by negligence and other human error factors, the plant should be installed in an independent room and staff/operators fully trained, made aware of potential risks and safety procedures thus minimising the risk of fire or explosion.Classifying Hazard Areas in Zones
Hazardous places are classified in terms of zones on the basis of the frequency and persistence of the potentially explosive atmosphere. This helps to determine the controls needed on potential sources of ignition that may be present or can occur in that zone.
From the fig 1 the schematic diagram of the pneumatic conveying system, dust and powders are classified in zones as follows
Zone 20 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is present continuously, or for long periods or frequently (Ansell Ray 2010).
The receiving vessel is classified as ZONE 20: Explosion is eminent since air mixed with powder can cause explosion if igniting source is present.
Conveying Pipeline is classified as ZONE 20: There is always enough powder inside the pipe and air mixed with the powder with the presence of an ignition source an explosion could occur.
The Blow Tank is classified as ZONE 20: Explosion is very likely if an igniting source is present since air is mixed with powder.
Zone 21 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is likely to occur in normal operation occasionally (Ansell Ray 2010).
Powder feeding station and discharge area is classified as ZONE 21: Explosion is likely to occur in normal operation occasionally if an igniting source is present. Caution should be taken so that explosion does not occur in an event of igniting source such as human or mechanical components due to friction.
Zone 22 - A place in which an explosive atmosphere in the form of a cloud of combustible dust in air is not likely to occur in normal operation, but if it does occur, it will persist for a short period only (Ansell Ray 2010).
The room where the Pneumatic conveying systems occupies is classified as ZONE 22: If there is a fault in the pneumatic conveying system, the powder could come out into the laboratory. Under normal conditions an explosion is not likely to occur in normal operation except in a circumstance where powder mixed with air in present of an igniting source.
Air compressor/Drier is classified as ZONE 22: Explosion is not likely to occur in normal operation however if it does it will persist only for a short period. It can also be classified as NO zone if the compressor is housed in a separate room from the conveyor system.
For an explosion to occur air, fuel (powder) and ignition source has to be present. To minimize the likelihood of an explosion, possible igniting sources have to be eliminated. Some of these sources include Sparks due to friction, trapped metal filings inside the pipeline, smoking, electrical sparks, static charges etc. Thus, to conclude the following assessment is done to be able to assess the risks and outline control measures:
LEGISLATIONS RELEVANT TO RISK ASSSESSMENT OF THE PLANT
There are many legislations but three are closely relevant to the risk assessment for fire and explosion. They include Health and Safety at work Act 1974 (HASAWA), Dangerous substance and Explosive Atmosphere Regulation 2002 (DSEAR) and the Management of Health and Safety at Work Regulations 1999 (MHSWR)Health and Safety at Work Act 1974
This is basis of British health and safety law. The act sets out the general duties which employers have towards employees and members of the public, and employees have to themselves and to each other. The duties are qualified in the Act by the principle of ' so far as is reasonably practicable' where employers have to take measure to avoid or reduce risk if they are technically impossible or if the time, trouble or cost of the measures would be grossly disproportionate to the risk (hse.gov.uk 2010)The Management of Health and safety at Work Regulation 1999
The main requirement on employers is to carry out risk assessment. The acts states that 'every employer shall make a suitable and sufficient assessment of the risk to the health and safety of his employees to which they are exposed whilst they are at work and the risk to the health and safety of person not in his employment arising out or in connection with the conduct by him or his undertaking' (hse.gov.uk 2010).The Dangerous Substances and Explosive Atmospheres Regulations 2002
Dangerous substance are any substance used or present at work that could, if not properly controlled, cause harm to people as a result of fire or explosion. The regulation requires employers to control the risks to safety from fire and explosions.
The regulation requires employers to
- Find out what dangerous substance are in the workplace and what are the fire and explosion risk.
- Put control measures in place to remove the risk or control them.
- Prepare plans and procedures to deal with accidents and emergencies.
- Make sure employees are properly informed and trained.
- Identify and classify areas of the workplace where explosive atmosphere may occur.
Part 2 (Maintenance)
Maintenance comprises of any actions other than routine services during operation that alters a product or system in such a way to keep the system in an operational condition if in a failed state (John Moubray 1994). Factors such as design, ageing, quality control, manufacture and usage can lead to the failure of a product or the likelihood of occurrence of failure.Types of Maintenance
There are two main types of maintenance actions: preventive maintenance and corrective maintenance.
Preventive maintenance is type of maintenance that generally requires shutdown of an operational system and are intended to increase the lifetime or its reliability (Babakalli Alkali 2009).
Corrective maintenance is type of maintenance that comprises of actions taken to restore a failed product or system to an operational state.
Preventive maintenance could either be condition-based or predetermined. Condition based maintenance will be used to schedule maintenance for the pneumatic conveying system. Condition based maintenance involves preventive maintenance initiated as a result of knowledge of the condition of an item from routine or continuous monitoring (Babakalli Alkali 2009).
MAINTENANCE OF THE SYSTEM
A permit to work system should be got before the maintenance work commences. The maintenance must be carried out with the plant shut down and all products removed.
The Valves: They require periodic removal examination and repair where necessary. The valves can be examined using visual inspection by the use of optical/computer based assistance or unaided eye. In terms of repair, manufacturer's specifications should be followed for maximum wear of parts.
The conveying pipe: Ultrasonic testing could be used to determine faults or anomalies in piping tubes by transmitting ultrasonic pulses or waves through the material and assessing the resultant. The pipe requires periodic examination and checks for cracks and corrosion.
Compressor: All components in the compressor should be maintained in accordance with the manufacturer specifications, filters and fluids replaced when faulty, leaks should be checked and belts adjusted where necessary.
The Blow Tank: This is a pressure vessel and it requires visual inspection or ultrasonic inspection for cracks and corrosion checks. There should be proper inspection and certification by the competent inspection authorities.
Suppression system: The manufacturer of the system should be consulted and a suitable maintenance schedule implemented. If the system operates it should be checked by the manufacturer and replaced after it has operated.Advantages of the Preventive Maintenance
- An early knowledge of impending failure through the use of trend analysis techniques.
- Actual knowledge and accurate failure prediction.
- This approach can pinpoint impending component failure together with the cause of the failure.
- It is flexible, if used with conjunction with an adaptive control and it can extend the useful life of plant /equipment.
A Job Safety Analysis (JSA) should be done before the maintenance to enable everyone get acquitted with the procedure of maintenance and safety.
All operators should be fully trained to be aware of the risk assessment and emergency safety procedures. A schedule for the planned maintenance of the plant and safe procedures for breakdown maintenance should be available.
Procedures should be in place to provide safety harness for working at height. Scaffold if erected must be inspected and checked.
LEGISLATIONS RELEVANT TO MAINTENANCE OF THE PLANT
There are many legislations but three are closely relevant to maintenance at work. They include Health and Safety at work Act 1974 (HASAWA), Working at Height Regulation 2005 (WAHR), the Control of Noise at Work Regulation 2005.Health and Safety at Work Act 1974
The act states that it shall be the duty of every employer to ensure, so far as is reasonable practicable, the health and welfare at work of all his employees, the provision and maintenance of plant and systems of work that are safe and without risks to health. The duty of the employee while at work to take reasonable care for health and safety of him and others who may be affected by acts or omission at work (hse.gov.uk 2010).Working at Height Regulations 2005
The regulation addresses all aspects of work at height including the selection and use of equipment, and the way the work is planned, organised and managed. The regulations are intended to minimise the risk of falls whilst working at height (hse.gov.uk 2010).Control of Noise at Work Regulation 2005
The regulation requires the employer to assess the risks to his employees from noise at work, take action to reduce the noise exposure that produces the risk, provide employees with hearing protection, provide employees with training, and carry out health surveillance where there is a risk to health. (hse.gov.uk 2010).
- Ansell Ray ( 2010) Safety and Safety Management handbook - ESDC509
- Babakalli Alkali (2009) Lecture note on Reliability Centred Maintenance
- HSE Regulations . Available from hse.gov.uk. Assessed on 23rd of April 2010
- Hughes P and Ferrett ED (2003), Introduction to Health and safety at work; the handbook for NEBOSH national general certificate. Elsevier Butterworth-Heinemann
- John Moubray. (1994) Reliability-Centred maintenance. ISBN 0750602309