Risk Assessment of Fire and Explosion Hazards - Essay Example

WORK Risk Assessment of Fire & Explosion Hazards and Associated Legislations In this report we shall first assess the risks of fire and explosion hazards in the pneumatic conveying system of a pharmaceutical powder called Pharmex. The report then shall briefly outline the relevant legislations for the given process. Figure.1 Pneumatic conveying is a clean and efficient way to move particulate solids (bulk solids, powders). In a basic conveying system there exists an air supply (often a compressor), a blow tank which delivers the powder and a pipeline which carries the powder to its destination. The powder is collected in a receiving vessel (hopper) from where it can be used in a further stage of the process. The receiving vessel is fitted with a filter to allow the air used in the pneumatic conveying process to be separated from the powder which collects in the receiving vessel. This pneumatic conveying system differs from a normal pneumatic conveying system in that the receiving vessel is placed above the blow tank system. A pipeline is used to transfer the pharmaceutical powder, Pharmex from the blow tank to receiver vessel to some distant area. A filter is used at the receiver tank and finally the powder settles down. The air compressor feeds the system with air under a desired pressure. In figure 1, the relief valves and the regulator valves are shown as PRF and NB respectively. Introduction Risk assessments are conducted in order to identify any fire & explosion hazards before the commencement of a process. Control of Substances Hazardous to Health (COSHH) (Health and Safety Executive, 2003) regulations is a useful tool for this work. It is imperative that employees be prevented from exposure to hazards. Implementation of COSHH regulations leads to: i. Higher productivity and efficiency by the use of more effective controls. ii. Improved employee morale. In this exercise, we will try to find out where there is enough powder present in this process for explosion to occur. Powder more than 80 gm/m3 is quite enough to have an explosion. The plant has powder transported from one area to another area by blowing it, which means the pipeline has the mixture of powder and air and thus possesses the potential of explosion. Explosive Atmospheres In pneumatic conveying system, workplace air and Pharmex can form the explosive atmospheres and this condition can be classified as hazardous area according to DSEAR (DSEAR 2002, SI 2002/2776). Therefore special precautions over ignition and fuel sources are required to prevent fire and explosions. Non hazardous area outside the workplace needs risk assessment as well. Hazardous areas are further classified as Zones which are included in DSEAR. When we talk about dangerous substance and explosive atmosphere regulations then we look at Zone. Zones Pharmex and air form a mixture in the process. Pharmex is susceptible to explosion. The mix of air and Pharmex is present continuously in the pneumatic conveyer system. Therefore, the apparatus is considered as Zone 20, according to DSEAR. To start the process we have to put the powder into the plant, as the powder is not present continuously, hence the filling of powder is in Zone 21 according to DSEAR. The proposed equipment for zone 20 is category 1 equipment, following DSEAR regulations. Risk Assessment First, the hazards that have potential to cause harm are identified. Secondly, the risks present to people’s health are assessed. Regarding the conveying system shown in figure 1, the main hazards are fire and explosion. Fire & Explosion Figure.2 The above triangle illustrates that igniting and burning a fire or causing an explosion requires three elements mentioned at the edge of the triangle. 1) Ignition source: The ignition source can be directly associated to heat. 2) Fuel: Is necessary for the fire or explosion to burn. 3) Oxidiser: Substances also necessary for the reaction of fire or explosion. Oxygen is the most common oxidiser. The fuel (Pharmex) and oxidation (air) are present at most places in the plant, hence the basis of safety will be: 1- The removal of ignition source. 2- Minimization of risk in the event of an explosion or fire. The explosibility properties vary for different substances. Most important are: Minimum ignition energy. It indicates the spark energy needed to ignite a powder cloud. Whilst most flammable liquids have values of less than two mL, hence can be ignited by almost any spark the energy require for igniting, different powder clouds can take a range of values. Maximum rate increase in of pressure and maximum explosion pressure indicate the severity of the explosion, if it occurs. Minimum explosible concentration is a range of concentrations where the powder cloud will not ignite even when an ignition source is available. Here, the pharmaceutical powder Pharmex and the explosibility properties are illustrated in the following table. Minimum ignition energy/mJ Maximum Pressure rise Bar rn/sec Maximum Explosion Pressure bar a Minimum explosible concentration g/m3 Pharmex 15 156 10 80 Kst (156 bar m/sec) indicates that the powder is moderately explosible. It means that explosion would have significant risks associated with it. Also, since the maximum explosion pressure value is above the normal range, i.e. l0 bar g which is dangerous. The minimum ignition energy is very low 15 mJ which can be generated easily for example by static personnel. The minimum explosible concentration 80 gm/m3 is in normal range which is not easily achieved. Identify people at risk: The employees at the plant premises and the public close to the workplace are the people at risk. Hazards associated with Plant components: The major fire and explosion hazards related to pneumatic conveying system are: 1. Blow Tank: A possible spark at the input/output of the blow tank could cause a fire in the pipeline. The blow tank is capable of sustaining an explosion since it is rated at 20barg while the MEP is l0barg. 2. The Pipe Line: The moving powder will not ignite as there will be insufficient time for a spark to transfer energy to the moving powder. Moreover, the powder is earthed by the pipeline. 3. Filter housing and receiving vessel: This can be considered as one unit or vessel. It is not capable to withstand the explosion as its rated pressure is 0.3barg, hence a suppression system is used to protect this unit in the event of an explosion. 4. Compressor: An isolation valve is needed to stop blow back to the compressor in the event of an explosion. Ignition Sources: As Pharmex is a fuel and oxidants are always present there exists a potential explosion or fire hazard whenever there is an ignition source. Ignition sources can be electrical, mechanical, thermal, or chemical. 1. Static ignition sources: Since Pharmex has the low minimum ignition energy, i.e. l5mJ care must be taken; there is a potential of ignition by static generated by personnel. To overcome this earthing the plant-conductive shoes are required to be worn. 2. Mechanical ignition source: Tramp metal in the powder can act as an isolated conductor and become charged to provide ignition source to the powder. To deal with it, filtering the powder is the best solution. Valves can overheat. 3. Electrical sources of ignition: Electrical equipment may provide the ignition source by way of spark or hot surface, for example incinerators, welding machine and flame-cutting, and heating appliances. 4. We have to check what are the other heat sources such as light bulbs or lamps situated close to combustible materials. 5. Smoking, smoking materials, candles or other naked flame sources used on the premises could be the source of ignition. Risk Evaluation An indication showing that the risk is related to the exposure is given by the formula: Risk = Hazard x Exposure After the identification of hazards, the maximum possible harm that the hazards can cause and the possibilities of the event are calculated. These two factors indicate towards estimation of risk as shown in table called the Simple Risk Level Estimator. Slightly harmful Harmful Extremely Harmful Highly Unlikely Trivial Risk Tolerable Risk Moderate Risk Unlikely Tolerable Risk Moderate Risk Substantial Risk Likely Moderate Risk Substantial Risk Intolerable Risk Table: Simple risk-level estimator Three categories of harm are mentioned in BS 8800: Slight Harm: Harm that is of a temporary nature, e.g. muscle strain, headache. Harmful: results in permanent minor disability, e.g. slight deafness, minor back problems, small reductions in lung function, Extreme harm: Premature death or permanent major disability, like loss of vision or limbs. Three categories of likelihood of harm have been mentioned in BS 8800: Highly Unlikely Unlikely Likely The substances with Maximum Exposure Limit (MEL) will require monitoring unless it can be proved that there is no significant risk involved in exceeding the MEL in the process concerned. Control Some of the measures that could be taken to minimize risks are: 1. The personnel should wear conductive shoes. 2. The Plant area should be restricted to the trained staff only. 3. All exits should be clear at all times. 4. Formulate a Maintenance Schedule to be followed rigorously. 5. Provide emergency lights on the premises. 6. Put up ‘Fire Exit’ signboards to clearly demarcate the exit routes. 7. Introduce fire detectors and carry out regular testing of fire alarm system. 8. Carry out a fire evacuation drill to effectively evaluate the fire exit system and procedures, and keep records. Legislation The relevant legislation formulated by the European Union for fire and explosion risks is DSEAR and ATEX. DSEAR DSEAR stands for the Dangerous Substances and Explosive Atmospheres Regulations 2002. Dangerous substances can put peoples’ safety at risk from fire and explosion. DSEAR defines duties of employers to protect people from risks and provide safety from fires, explosions and similar events. It also includes members of the public who may be put at risk by work activity. DSEAR defines dangerous substances as any substances used or present at work that could, if not properly controlled, cause harm to people as a result of a fire or explosion. They are found in almost all workplaces, e.g. solvents, paints, varnishes, flammable gases such as LPG, dusts from sanding, etc. As per DSEAR, it is the responsibility of the employer to carry out risk assessments and take the suitable actions to ensure safety in workplace for the workers and the public. In this risk assessment, the most important regulation of DSEAR is regulation 7. The regulation 7 classifies places where explosive atmospheres may occur, outlines the guidelines for the selecting equipment, protective systems and warning signs for places where explosive atmospheres may occur. ATEX ATEX is the name commonly given to the framework for controlling explosive atmospheres and the standards of equipment and protective systems used in them. It is based on the requirements of two European Directives: 1. Directive 99/92/EU (also known as ‘ATEX 137’ or the ATEX Workplace Directive’) on the minimum requirements for improving the health and safety protection of workers potentially at risk from explosive atmospheres. 2. Directive 94/9/EU (also known as ‘ATEX 95’ or ‘the ATEX Equipment Directive’) applies to all equipment intended for use in explosive atmospheres, whether electrical or mechanical, and also to protective systems. Safety devices intended for use outside explosive atmospheres required for or contribute to the safe functioning of equipment or protective systems with respect to risks of explosion are also included. This is an increase in scope compared to former national regulations for equipment and systems intended for use in potentially-explosive atmospheres. The recommendations of the Directive were implemented in Great Britain through the DTI’s Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996 (SI 1996/192). COURSEWORK 2 Maintenance Schedule for the Plant The Control of Major Accident Hazards (COMAH) regulations are the suitable guidelines to develop the maintenance schedule. The following factors are taken into consideration while formulating maintenance procedures: Human factors Conscious and unconscious incompetence Effective maintainability principles Know-how of failure rate and maintainability Clear and well-defined criteria for identifying faults and marginal performance. Guidance and Codes of Practice relating to maintenance procedures The following publications can be used as guidance material relating to maintenance procedures (Health and Safety Executive, 2011): HS(G)22 Electrical apparatus for use in potentially-explosive atmospheres, HSE, Not in current HSE list. Paragraph 49 points towards the importance of good engineering practice and knowledge of the maintenance history for any electrical apparatus with explosive protection capabilities. Para 51 refers to BS 5345 (Code of Practice for the selection, installation and maintenance of electrical apparatus for use in potentially-explosive atmospheres (in 8 parts)) which lists the typical maintenance schedules for each type of electrical apparatus. Para 52 refers to a routine checklist that should regularly be applied to any electrical equipment used in potentially-explosive atmospheres. Paragraph 55 refers to the need to recognise the correct explosive markings on a piece of electrical equipment so that the correct type of maintenance can be applied. HS(G)71 Chemical warehousing: the storage of packaged dangerous substances, HSE, 1998. Paragraph 54 refers to the importance of contractor competence to mitigate hazards that may be created during maintenance and repair. Proposed Maintenance Schedule As per the BS Standards, the maintenance of the electrical works and fittings in explosive atmospheres should be carried out periodically. The recommendation for period is two years or more frequently for installations in ‘particularly arduous environmental conditions.’ Points worthy of note are mentioned here and they clarify some of the requirements of IEC 60079-17: Use of properly trained personnel as per the prerequisite for carrying out inspections. Initial inspection is to be verified that the installation meets all requirements of the area classification, apparatus grouping and temperature classification as defined by the plant owners. The installation must comply with the (design) documentation and special conditions of installation if any must be take into account. All apparatus be properly identified and labelling must be correct. Apparatus must not be damaged after installation. Earthing shall be in accordance with clause 16 of the British Standards. Cable screens are to be in accordance with relevant documentation and clause 16. Interfaces should be properly fitted (meaning according to the manufacturer’s instructions). Interface and junction boxes are to be inspected to check if they contain no non-IS circuits. Cabling is to be inspected to ensure that only IS cables are used in multicore cables, and protection is afforded where necessary. In addition to these guidelines of electrical maintenance, some other guidelines to be followed are: 1. Regular check of the valves for leakages and fractures. 2. Check the Blow Tank, Receiver Vessel and conveying pipeline for corrosion and rust. 3. Check the pressure gauges and thermocouples for accurate measurements of the process conditions and avoid any mishap due to faulty recordings of data. 4. Regularly check the fire extinguisher and review fire exit procedures to minimize risk during a mishap. Legal The relevant guidelines are outlined in the legislation Health and Safety at Work etc. Act 1974. It outlines the different duties of employers and employees and the duties towards articles and substances used at work. Section 2 defines the duties of the employer. It states that "It shall be the duty of every employer to ensure, so far as is reasonably practicable, the health, safety and welfare at work of all his/her employees", and in particular that such a duty extends to: Maintenance of plant and systems of work that are, so far as is reasonably practicable, safe and without risks to health; So far as is reasonably practicable as regards any place of work under the employer’s control, the maintenance of it in a condition that is safe and without risks to health and the provision and maintenance of means of access to and egress from it that are safe and without such risks; Provision and maintenance of a working environment for his employees that is, so far as is reasonably practicable, safe, without risks to health, and adequate as regards facilities and arrangements for their welfare at work. Section 6(1) outlines the duties of people responsible for designs, manufactures, imports or supplies any article for use at work to: Ensure, that the article is so designed and constructed that it will be safe and without risks to health at all times when it is being set, used, cleaned or maintained by a person at work; Perform testing and examination to ensure safety; Take steps to ensure that persons supplied with the article are provided with adequate information about the proper use of article for which it is designed, or has been tested, and about any conditions necessary to ensure that it will be safe and without risks to health at all times, including when it is being dismantled or disposed of. Under Section 7 all employees have a duty while at work to: Take reasonable care for the health and safety of him/herself and of other persons who may be affected by his/her acts or omissions at work; and Co-operate with employers or other persons so far as is necessary to enable them to perform their duties or requirements under the Act. Bibliography Health and Safety Executive (2003). COSHH essentials: Easy steps to control chemicals. Control of Substances Hazardous to Health Regulations (HSG193) (2nd ed.). London: HSE books. The Dangerous Substances and Explosive Atmospheres Regulations 2002. SI 2002/2776, London: HMSO. International Standards Office, 1994. ISO 9001 - Quality management systems — Requirements. Geneva: ISO. British Standards Institution, 1999 . OHSAS 18001:1999, Occupational health and safety management systems Specification. London: BSI. HSE, 1992. Dangerous Maintenance - A Study of Maintenance Accidents and how to prevent them, London: HSE Books. Council Directive 94/9/EC of 23 March 1994 on the approximation of the laws of the Member States concerning equipment and protective systems intended for use in potentially explosive atmospheres Health and Safety Executive, 2011. Control of major accident hazards (COMAH.) [online] Available at: www.hse.gov.uk/comah/ [Accessed 20 April 2011]. Health and Safety at Work etc. Act 1974. (c.37), London: HMSO. Read More