Health & Safety Management for Quarries Topic Five Risk Assessment & Management Objectives of this Section Introduce the concept of risk assessment and risk management and its role within UK health and safety legislation. To define the principle components of risk management. To outline advanced risk assessment methodologies for use in QRAs. To outline a practical risk assessment process.
Principals of Risk Management Risk management can be defined as: The eradication or minimisation of the adverse affects of risks to which an organisation is exposed. Stages in Risk Management Identifying the hazards. Evaluating the associated risks. Controlling the risks. RISK MANAGEMENT RISK REDUCTION RISK ASSESSMENT Activity Characterisation
Decision Making RISK EVALUATION Audit or Review Regulation 3(1) of the Management of Health and Safety at Work Regulations 1992 states: Every Employer shall make a suitable and efficient assessment of:a) The risks to the health and safety of his employees to which they are exposed whilst they are at work. b) The risks to the health and safety of persons not in his employment arising out of or in connection with the conduct by him or his undertaking; For the purpose of identifying the measures he needs to take to comply with the requirements and prohibitions imposed on him by or under the relevant
statutory provisions. Risk assessment can be a very straightforward process based on judgement requiring no specialist skills or complicated techniques. This approach is commonly known as qualitative or subjective risk assessment. Major Hazards Major hazards associated with complex chemical or nuclear plants, may warrant the need of such techniques as Quantitative Risk Assessment. In Quantitative Risk Assessment (QRA) a numerical estimate is made of the probability that a defined harm will result from the
occurrence of a particular event. The Risk Management Process Hazard Identification Hazard : The potential to cause harm. Harm including ill health and injury, damage to property, plant, products or the environment, production losses or increased liabilities. Hazard Identification Comparative Methods. e.g. checklists and audits. Fundamental Methods: e.g. Deviation Analysis, Hazard and Operability Studies, Energy Analysis, Failure Modes & Effects Analysis.
Failure Logic: e.g. Fault Trees, Event Trees & Cause- Consequence diagrams Assessing the Risks Risk: The likelihood that a specified undesired event will occur due to the realisation of a hazard by, or during work activities or by the products and services created by work activities. Assessing the Risks Quantitative risk assessment Commonly used in the high technology industries QRA tends to deal with the avoidance of low probability events with serious
consequences to the plant and the surrounding environment. Assessing the Risks Subjective risk assessment Qualitative risk assessment involves making a formal judgement on the consequence and probability using: Risk = Severity x Likelihood Assessing the Risks Example: The likely effect of a hazard may for example be rated: 1. Major Death or major injury or illness causing long term disability 2. Serious Injuries or illness causing short-term disability
3. Slight All other injuries or illnesses Assessing the Risks The likelihood of harm may be rated 1. High Where it is certain that harm will occur 2. Medium Where harm will often occur 3. Low Where harm will seldom occur Assessing the Risks Risk = Severity of Harm x
Likelihood of occurrence This simple computation gives a risk value of between 1 and 9 enabling a rough and ready comparison of risks. In this case the lower the number, the greater the risk, and so prioritises the hazards so that control action can be targeted at higher risks. Controlling Risk Risk Avoidance This strategy involves a conscious decision on the part of the organisation to avoid completely a particular risk by discontinuing the operation producing the risk e.g. the replacing a hazardous chemical by one with less or no risk potential. Risk Retention The risk is retained in the organisation where any consequent loss is financed
by the company. There are two aspects to consider here, risk retention with knowledge and risk retention without knowledge. Controlling Risk Risk Transfer This refers to the legal assignment of the costs of certain potential losses from one party to another. The most common way is by insurance. Risk Reduction Here the risks are systematically reduced through control measures, according to the hierarchy of risk control described in earlier sections. ALARP Legislation requires employers to reduce risks
to a level that is as low as is reasonably practicable (sometimes abbreviated as ALARP). To carry out a duty so far as is reasonably practicable means that the degree of risk in a particular activity or environment can be balanced against the time, trouble, cost and physical difficulty of taking measures to avoid the risk. Types of Risk Assessment Within Industry, three types of risk assessment can be distinguished: Assessments of large scale complex hazard sites, such as those found in the process and nuclear industries. These require QRAs General assessments of the complete range of
workplace risks as required under the Management of Health & Safety at Work Regulations, 1999. Risk Assessments required under specific legislation for example for hazardous substances (COSHH Regulations, 1998), Manual Handling (Manual Handling Operations Regulations, 1992). Advanced Risk Assessment Techniques Quantitative Risk Assessment QRA is most commonly used in the process industries to quantify the risks of major hazards. QRA used in the offshore oil and gas industries, the transport of hazardous materials, the protection of the environment, mass transportation (rail) and the nuclear industry.
Quantitative Risk Assessment (1) Individual Risk is defined as the frequency at which an individual may be expected to sustain a given level of harm from the realisation of specific hazards. Societal Risk Usually expressed as risk contours: 0.3*10-6/year risk contour VILLAGE Site for proposed developmen
t 10-5/year risk contour CHLORINE INSTALLATION 1 km 10-6/year risk contour Quantitative Risk Assessment: Acceptance Criteria The HSE state that broadly, a risk of death of 1 in 1000 (1x10 -3) per annum is about the most that is ordinarily accepted under modern conditions for
workers in the UK and it seems to be the dividing line between what is tolerable and what is intolerable. Failure Modes and Effect Analysis The system is divided into sub systems that can be handled effectively. It involves: Identification of the component and parent system. Failure mode and cause of failure. Effect of the failure on the subsystem or system. Method of detection and diagnostic aids available.
Failure Modes and Effect Analysis A typical format: Component Function Failure Mode Failure Rate Failure Effect Criticality
Detection Method Preventative Measures Failure Modes and Effect Analysis For each components functions, every conceivable mode of failure is identified and recorded. It is also common to rate the failure rate for each failure mode identified. The potential consequences for each failure must be identified along with its effects on other equipment, components within the rest of the system. It is then necessary to record preventative measures that are in place or may be introduced to correct the
failure, reduce its failure rate or provide some adequate form of detection. Hazard & Operability Studies Hazard and Operability Studies (HAZOP) have been used for many years as a formal means for the review of chemical process designs. A HAZOP study is a systematic search for hazards which are defined as deviations within these parameters that may have dangerous consequences. In the process industry, these deviations concern process parameters such as flow, temperature, pressure etc. Hazard & Operability Studies
HAZOP is a team approach, involving a team of people representing all different functions in a plant. They identify all the deviations by brain-storming to a set of guide words which are applied to all parts of the system. Hazard & Operability Studies The process is as follows: The system is divided into suitable parts or sub-systems, which are then analysed one at a time. For each sub-system each parameter (flow, temperature, pressure, volume, viscosity etc.) that has an influence on it, is noted. Guidewords are applied to each parameter in each subsystem. The intention is to prompt creative discussion of deviations and possible consequences
For each significant deviation, possible causes are identified. Hazard & Operability Studies Guideword Definitions NO or NOT No part of the design intent occurs, such as no flow in a pipeline due to blockage. MORE or LESS A quantitative increase or decrease of some parameter, such as flow, temperature etc.
AS WELL AS All the design intentions are fulfilled and something happens in addition PART OF Only part of the design intention is fulfilled REVERSE The logical opposite of the design intention occurs OTHER THAN Something completely different than attended occurs
Hazard & Operability Studies Example Consider the simple process diagram below. It represents a plant where substances A and B react with each other to form a new substance C. If there is more B than A there may be an explosion. V3 V4 B A V2 V1
V5 A < B = Explosion C Example from Harms Ringdahl L (1995), Safety Analysis: Principals and Practice in Occupational Safety, Elsevier Applied Science. The HAZOP sheet for the section of the plant from A to C will be as follows: Guide Word Deviation Possible Causes
Consequences Proposed Measures NO, NOT No A Tank containing A is empty. V1 or V2 closed. Pump does not work. Pipe broken Not enough A = Explosion
Indicator for low level. Monitoring of flow MORE Too much A Pump too high capacity Opening of V1 or V2 is too large. C contaminated by A. Tank overfilled. Indicator for high level.
Monitoring of flow LESS Not enough A V1,V2 or pipe are partially blocked. Pump gives low flow or runs for too short a time. Not enough A = Explosion See above AS WELL AS
Other substance V3 open air sucked in Not enough A = Explosion Flow monitoring based on weight REVERSE Liquid pumped backwards
Wrong connector to motor Not enough A = Explosion A is contaminated Flow monitoring OTHER THAN A boils in pump Temperature too high
Not enough A = Explosion Temperature (and flow) monitoring. Example from Harms Ringdahl L (1995), Safety Analysis: Principals and Practice in Occupational Safety, Elsevier Applied Science. Fault Tree Analysis A fault tree is a diagram that displays the logical interrelationship between the basic causes of the hazard. Fault tree analysis can be simple or complex depending on the system in question. Complex analysis involves the use of Boolean algebra to
represent various failure states. Fault Tree Analysis The first stage is to select the hazard or top event that is to be analysed. The tree is structured so that the hazard appears at the top. It is then necessary to work downwards, firstly by identifying causes that directly contribute to this hazard. When all the causes and sub-causes have been identified, the next stage is to construct the fault tree. Fault Tree Analysis Symbol Designation
Function EVENT / CAUSE Causes or events that can be developed further BASIC EVENT/CAUSE Basic or Root Causes or events that cannot be developed further UNDEVELOPED EVENT/CAUSE Causes are not developed due to lack of
information or significance. AND gate Output event occurs only if all input events occur OR gate Output event occurs if any one of the input events occurs Fault Tree Analysis Example Consider the simple circuit diagram shown below: LAMP
POWER UNIT + BATTERY - FUSE SWITCH Example from Harms Ringdahl L (1995), Safety Analysis: Principals and Practice in Occupational Safety, Elsevier Applied Science. Fault Tree Analysis The corresponding fault tree for the above circuit, with the top
event (or hazard) being the lamp not working is as follows: Lamp does not light No current through the lamp Faulty Lamp No power supply to the lamp Broken circuit No power feed No Power
from battery No Power from unit Broken Circuit Defective switch Defective fuse Example from Harms Ringdahl L (1995), Safety Analysis: Principals and Practice in Occupational Safety, Elsevier Applied Science.
Practical Risk Assessment (from BS8800) Classify work activities Identify hazards Determine risk Decide if risk is tolerable Prepare risk control action plan (if necessary) Review adequacy of action plan Classify Work Activities Possible ways of classifying work activities
include: Geographical areas within/outside the organisation's premises. Stages in the production process, or in the provision of a service. Planned and reactive work. Defined tasks (e.g. driving). BS8800:1996 Identify Hazards Broad categories of hazard To help with the process of identifying hazards it is useful to categorise hazards in different ways, for example by topic, e.g.:
Mechanical. Electrical. Radiation. Substances. Fire and explosion. BS8800:1996 Hazards prompt-list During work activities could the following hazards exist?
Slips/falls on the level. Falls of persons form heights. Falls of tools, materials, etc., from heights. Inadequate headroom. Hazards associated with manual lifting/handling of tools, materials, etc.. Hazards from plant and machinery associated with assembly, commissioning, operation, maintenance, modification, repair and dismantling. BS8800:1996 Hazards prompt-list Vehicle hazards, covering both site transport, and travel by road. Fire and explosion.
Violence to staff. Substances that may be inhaled. Substances or agents that may damage the eye. Substances that may cause harm by coming into contact with, or being absorbed through, the skin. Substances that may cause harm by being ingested (i.e., entering the body via the mouth). Harmful energies (e.g., electricity, radiation, noise, vibration). BS8800:1996 Hazards prompt-list Work-related upper limb disorders resulting from frequently repeated tasks. Inadequate thermal environment, e.g. too hot. Lighting levels. Slippery, uneven ground/surfaces.
Inadequate guard rails or hand rails on stairs. Contractors' activities. BS8800:1996 Determine risk The risk from the hazard should be determined by estimating the potential severity of harm and the likelihood that harm will occur. Severity of harm Information obtained about work activities is a vital input to risk assessment. When seeking to establish potential severity of harm, the following should also be considered: Part(s) of the body likely to be affected;
Nature of the harm, ranging from slightly to extremely harmful: 1) Slightly harmful, e.g.: Superficial injuries; minor cuts and bruises; eye irritation from dust. Nuisance and irritation (e.g. headaches); ill-health leading to temporary discomfort. BS8800:1996 Severity of harm 2) Harmful, e.g. Lacerations; burns; concussion; serious sprains; minor fractures. Deafness; dermatitis; asthma; work related upper limb disorders; ill-health leading to permanent minor disability. 3) Extremely harmful, e.g. Amputations; major fractures; poisonings; multiple
injuries; fatal injuries. Occupational cancer; other severely life shortening diseases; acute fatal diseases. BS8800:1996 Likelihood of harm When seeking to establish likelihood of harm the adequacy of control measures already implemented and complied with needs to be considered. Issues considered: Number of personnel exposed. Frequency and duration of exposure to the hazard. Failure of services e.g. electricity and water. Failure of plant and machinery components and safety devices. Exposure to the elements.
BS8800:1996 Likelihood of harm Protection afforded by personal protective equipment and usage rate of personal protective equipment; Unsafe acts (unintended errors or intentional violations of procedures) by persons, for example, who: 1) May not know what the hazards are. 2) May not have the knowledge, physical capacity, or skills to do the work. 3) Underestimate risks to which they are exposed. 4) Underestimate the practicality and utility of safe working methods. BS8800:1996
Decide if risk is tolerable One simple method for estimating risk levels and for deciding whether risks are tolerable. Risks are classified according to their estimated likelihood and potential severity of harm. Slightly harmful Harmful Extremely harmful Highly unlikely TRIVIAL RISK
Likely MODERATE RISK SUBSTANTIAL RISK INTOLERABLE RISK BS8800:1996 Prepare risk control action plan Risk categories shown form the basis for deciding whether improved controls are required and the timescale for action.
The outcome of a risk assessment should be an inventory of actions, in priority order, to devise, maintain or improve controls. BS8800:1996 A simple risk-based control plan. RISK LEVEL TRIVIAL ACTION AND TIMESCALE No action is required and no documentary records need to be kept. TOLERABLE No additional controls are required. Consideration may be given to a more cost-effective solution or improvement that imposes no
additional cost burden. Monitoring is required to ensure that the controls are maintained. MODERATE Efforts should be made to reduce the risk, but the costs of prevention should b e carefully measured and limited. Risk reduction measures should be implemented within a defined time period. Where the moderate risk is associated with extremely harmful consequences, further assessment may be necessary to establish more precisely the likelihood of harm as a basis for determining the need for improved control measures. Work should not be started until the risk has been reduced. Considerable resources may have to be allocated to reduce the risk. Where the risk involves work in progress, urgent action should be
taken. SUBSTANTIAL INTOLERABLE Work should not be started or continued until the risk has been reduced. If it is not possible to reduce risk even with unlimited resources, work has to remain prohibited. BS8800:1996 Prepare risk control action plan The action plan should be reviewed before implementation, typically by asking:
Will the revised controls lead to tolerable risk levels? Are new hazards created? Has the most cost-effective solution been chosen? What do people affected think about the need for, and practicality of, the revised preventive measures? Will the revised controls be used in practice, and not ignored in the face of, for example, pressures to get the job done? BS8800:1996 Changing Conditions and Revising Risk assessment should be seen as a continuing process. Thus, the adequacy of control measures should be subject to
continual review and revised if necessary. BS8800:1996
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