1. INTRODUCTION
This paper was developed to assist in the identification and control of safety and health risks associated with hours of work arrangements for the mining industry. Changes in the design of work schedules have resulted in the extension of work hours with sometimes a decrease in the numbers of days worked. The mining industry is under increased pressure to compete more effectively globally, which may require changes to work structures to enhance productivity and reduce costs. The introduction of extended shifts has been one of the responses of the mining industry to meet the changing structure of work.
Twenty-four hour operations pose distinct challenges to human physiology, particularly for personnel working in hazardous environments. Irregular work and sleep patterns are associated with increased work-related fatigue, decreased alertness and increased accident risk, especially in the early morning hours. Where risks to safety and health are increased through hours of work arrangements, both employers and employees must take the necessary steps to address them.
This joint responsibility needs to be appreciated if the mining industry is to function in a safe and healthy working environment. Both employees and employers should cooperate to achieve this objective. Surveys conducted in 1999 by the Queensland Department of Mines and Energy and the Australian Centre for Industrial Relations, Research and Training (ACIRRT) indicated that in Queensland, greater than 80% of the mine workers were working greater than eight hours per work shift. The balance of workers (~ 20%) were on shift rostering systems of eight hours or less.
The locations of Queensland mines are mixed. Approximately 55% are located in mixed community settings and 23% in isolated communities. Approximately 20% are fly in/fly out or drive in/drive out operations (ACIRRT, 2000). The characteristics of the Queensland mining industry in terms of location and roster patterns show that shiftwork is a vital part of the industry and as such the risks associated with hours of work
arrangements must be managed.
1.1 Purpose
To provide practical guidance to companies, employers and employees on how to minimise and control risks arising from the hazards associated with hours of work arrangements.
1.2 Scope
The scope of the paper is limited to the management of hazards related to hours of work arrangements and the effect on the safety and health of individuals and workplaces
2. WHAT IS COVERED BY HOURS OF WORK ARRANGEMENTS
It is difficult to arrive at a simple definition of hours of work arrangements as these arrangements include:
- Scheduling of rosters;
- Number of consecutive shifts;
- Maximum hours per shift;
- Maximum hours per roster cycle;
- Start and finish times;
- Break patterns within and between shifts;
- Factors affecting the health and safety of workers.
These factors are important in any shift pattern, even work arrangements not normally classified as shiftwork. These factors need to be considered in the risk management of hours of work arrangements. Extended workdays refer to work schedules having longer than normal workdays. Some sources consider it to be between 8 to 12 hours in length, however, there is no clear consensus about the length of the extended workday.
Workers on extended shifts often work fewer than five days a week. When the traditional 36 to 40 hour work week are compressed into three or four days, the number of days worked in a row is decreased and the number of consecutive days off is increased. This is not always the case - working an extended shift pattern does not automatically mean the same as a compressed work week.
2.1 Commuter Operations
At remote mine sites, workers typically stay in accommodation close to the mine site and only commute at the beginning and end of the roster. This is becoming more commonplace with many operations adopting this practice. This paper has been prepared in recognition of the special characteristics and needs of both fly in/fly out and drive in/drive out mining operations that operate outside of the traditional standard working week.
The difference between commuter operations and other work schedules where workers return to the community during non-working time should be recognised and a holistic approach to workplace safety and health adopted. There are potential benefits in addition to the potential increase in some risks when comparing fly in/fly out operations to daily commute operations.
3. EFFECTS OF HOURS OF WORK ARRANGEMENTS
3.1 Health, family and community
3.1.1 Body Clock
Like other living organisms, humans have natural body rhythms that are regulated by a “circadian clock” in the brain. These are called circadian rhythms. Over a 24-hour period the circadian clock regulates sleep/wake patterns, body temperature, hormone levels, digestion and many other functions.
Depending on the time of day or night, the human body is programmed for periods of wakefulness and sleep, high and low body temperature, high and low digestive activity, and so on. Adults tend naturally to sleep by midnight, wake near dawn, and stay awake through the day (with an afternoon sleepy period). Body temperature is at its lowest between 2 am and 6 am. The ability to concentrate and perform tasks is also at its lowest in these early hours of the morning, parallelling the fall in core body temperature. This pattern is repeated every 24 hours.
Disrupted rhythms impact on the quantity and quality of sleep, task performance and create a perceived sense of personal imbalance. Shiftwork can be considered to be a biological disruptor. Generally no complete physiological (body function) adaptation takes place for the majority of night workers. A majority of night workers suffer ongoing sleep problems.
3.1.2 Sleep and Fatigue
Human fatigue (represented by decreased physical and mental capacity) is multifactorial. Symptoms of fatigue include tiredness even after sleep, psychological disturbances, disinclination to work and general loss of vitality. This may lead to chronic disruptive sleep patterns and body systems alterations (gastric ulcers etc).
Disruptions to normal sleep routines are often associated with night shift or extended hours, where the major difficulty is getting adequate undisturbed sleep during the day, particularly in hot climates. The cumulative result of these disruptions is insufficient recovery sleep, commonly known as sleep debt leading to increased fatigue and decreased performance. From a safety and health perspective, fatigue is most appropriately conceptualised as either workrelated or non-work-related, and may be defined as the increasing difficulty to perform physical or mental activities.
(a) Work related fatigue
Examples of work related fatigue might arise from situations requiring concentration for extended periods during work hours, working in temperature extremes or working in high-risk situations. Levels of work-related fatigue may be considered to be more similar across different individuals performing the same tasks than non-work related fatigue. This follows because there are fewer variables for individuals doing the same task in the same environment than in a nonwork situation. Work-related fatigue as defined in this paper can be measured and managed at an organisational level.
(b) Non-work related fatigue
Examples of non-work related fatigue include sleep disruption due to ill family members, stress associated with financial difficulties, moonlighting, domestic responsibilities or many other factors. Non-work-related fatigue because of all the different circumstances will be highly variable between individuals and is dependent on a person’s environment in addition to their physical and mental attributes. Non-workrelated fatigue is best managed at the individual level.
Employers should provide access to information that allows their employees to make informed lifestyle choices. By providing relevant and accurate information, employers are more likely to minimise the impacts of non-work-related fatigue on work activities.
Effective management for work related and nonwork-related fatigue is likely to produce benefits to the organisations, employees, their families and communities. Organisations may receive improvements in morale, safety, productivity and attrition rates. Individuals can expect benefits to health, well being, motivation and quality of life.
3.1.3 Effects on Health
Long - term exposure to shiftwork may have deleterious effects on the health of individuals. Evidence from studies of shift workers indicate a higher incidence of:
- Gastrointestinal disorders (eg peptic ulcers, heartburn, nausea)
- Cardiovascular disease (eg Ischaemic heart disease, high blood pressure)
- Complaints associated with stress (eg anxiety, depression)
Those already suffering from digestive disorders, diabetes, heart diseases, psychological problems, alcohol and drug addictions and chronic sleep disturbances face additional burdens.
(a) Medication
Generally, there is an assumption that prescription medication is used during the day and that sleep occurs at night. For shift workers this may not be the case. It is important to understand that the effects of medication are related to the time-of-day at which they are taken. Depending on the individual roster, the intended effect of the prescribed medication may vary from the actual outcome. Workers should advise medical practitioners
about the status of working hours when being prescribed medication.
3.1.4 Effects on family and social life
Work scheduling that is based solely on organisational requirements may not acknowledge the personal, domestic and social needs of its workforce. In many cases, shift workers find it difficult to maintain a satisfactory social and family life and many neglect recovery from work in order to fulfil other needs. The dislocation of family and social life may result in pressures on relationships, domestic workloads and community activities. As with sleep and fatigue, this has implications for task performance, safety and health, morale, absenteeism, productivity and attrition rates. Good roster design may minimise these impacts.
3.2 Work Performance and Safety
3.2.1 Sleep deficit
Getting adequate undisturbed sleep during the day may be difficult during periods of night work. Extended hours that carry into night period may create a similar problem. The cumulative result of these disruptions is lack of sufficient sleep, which may lead to what is called sleep debt. If a worker is seriously sleep deprived, they may suffer micro sleeps. Micro-sleep is a briefnap that lasts for around 4 to 5 seconds. The worker may not have realised that sleep has occurred. These could have a significant impact on safety.
3.2.2 Roster Organisation
While there is no “right” or “wrong” roster design, good management practice in the design of rosters can facilitate a balance between maximising productivity and ensuring the safety and health of the workforce. Decisions to change roster design are more likely to be more successful if they are preceded by consultation with the workforce on the justification for the change. This consultation may be supported by an education and information program to enable full appreciation of the implications and purpose of the change.
(a) Direction of rotation
The human body has difficulty in adjusting to changing work routines. Evidence suggests that the body can adapt easier to going to sleep later (forward rotation) rather than earlier (backward rotation). This is somewhat dependent on individual preferences and circumstances and the evidence in this field is inclusive.
(b) Speed of rotation
The speed of rotation describes the number of days an individual spends on a particular shift before a change to another shift or to time off periods occurs. A slowly rotating schedule, working 3 to 4 weeks on the same shift, allows greater time for body rhythms to adjust and adapt. As the quality of sleep is lower when working night shift, such long cycles may create an accumulating sleep debt and fatigue problem. This can be exacerbated if workers return to a day routine on their days off. A faster rotation may enable the employees to minimise circadian movement, as the body does not have time to adjust to differing shift times. Such rapid rotations minimise the accumulation of a large sleep debt as long periods of night shifts are avoided.
(c) Irregular and unpredictable work schedules
It is generally more favourable to have a regular and predictable work scheduling arrangement. Unpredictable work schedules may also compromise the quality of rest time if there is the continual possibility of recall to duty. Where on-call arrangements are used, on-site facilities should maximise the opportunity for undisturbed rest and sleep.
3.2.3 Work scheduling
Scheduling the work of employees to minimise the impact of safety and health risks to all stakeholders is essential.
(a) Recovery within and between work periods
Within a period of work, breaks should be taken to allow for mental and physical time away from the work environment. Potentially this may lead to improved vigilance, performance, safety and efficiency. Lack of suitable recovery periods between shifts may be viewed as a major potential hazard. This is particularly the case between night shifts. The value of a break, with a set duration, between shifts is dependent on the time of day at which the break commences. Minimum break duration should acknowledge the time of day impacts.
(b) Type of work and workloads
Research indicates that certain types of tasks are performed better at particular times of the day than others. Performance reduction with particular types of tasks can be modified by factors such as the activity duration and intrinsic nature of the work. When extended shifts are used, the following must be carefully considered if risk to safety and health is to be kept to an acceptable level:
- Level of risk inherent risk associated with the work;
- Level of mental or physical effort required;
- Exposure to hazards where safety standards are based on 8 hour exposures;
- Work that is tied to short cycle operations;
- Work that requires extended periods of vigilance.
Studies show overtime after 12 hour shifts is a high-risk practice and should not be worked other than in emergencies.
3.2.4 Travel time
In addition to the actual contact hours at work, travel time to and from work each day should be considered particularly when extended shifts are worked. In some instances travelling time can significantly extend the effective length of a shift. Sleep time is reduced and recovery times at the end of shift rosters may be reduced.
Hazards associated with persons driving on long straight desolate stretches or road are a problem especially when fatigued.
3.2.5 Safety
Consideration of the potential effects on safety of shiftwork involves consideration of two separate issues. The first is related to the problem of fatigue and its influence on behaviour associated with safe work practices resulting in accident or injury. The second issue relates to the problem of prolonged exposure to physical, chemical and other hazards in the working environment.
(a) Accidents and incidents
Four basic situations have been identified where shift workers need to perform at their optimum and where fatigue may play an important role.
- Where work error is dangerous to society
- Where work error is dangerous to the worker or workers themselves
- Where a failure to respond is dangerous to society
- Where failure to respond is dangerous to the worker or workers themselves
These are the situations that need to be identified and assessed in order to effectively manage the safety risks associated with shiftwork and fatigue. One of the identified problems with determining the effect of shiftwork on accident and injury rates in the mining industry is the lack of data available. Data should be collected that allows analysis to determine if the shift roster system or the length of the shift may have contributed to the accident or incident.
(b) Exposure to hazardous substances
The effects of extended exposure to hazardous substances for workers is another issue that needs consideration with regard to rosters and scheduling of extended shifts, particularly when long durations of extended shifts are scheduled. The national and international exposure standards for toxic chemicals are based on an eight-hour day, five day per week. This leaves the question of necessary adjustment to accommodate working hours outside the standard week to be addressed.
3.2.6 Moonlighting
One unexpected outcome of compressed work schedules may be moonlighting, in which employees take additional employment on their days off or during leisure time. Moonlighting is difficult to control, impacts on the management of fatigue and should be of concern to the mining industry.
3.3 Commuter operations
Commuting to work either by fly in/fly out or drive in/drive out is becoming more commonplace. This mode of operation has both pluses and minuses and while many of the safety and health concerns associated with extended shifts have been addressed there are some issues specific to commuter operations that warrant attention especially as these often coincide with greater number of consecutive shifts.
Many operations have in place risk management processes. Examples of risk management frameworks that could be used include:
- Australian/New Zealand Standard - AS/NZS 4360:1995;
- Risk Management; MDG 1010: Risk Management Handbook for the Mining Industry, Department of Mineral Resources, New South Wales;
- Workplace Health and Safety Risk Management Advisory Standard 2000, Department of Employment, Training and Industrial Relations, Queensland.
Typical processes for the management of risk comprises three steps:
(1) Risk analysis
(2) Risk assessment
(3) Risk control
4. RISK MANAGEMENT OF HOURS OF WORK ARRANGEMENTS
4.1 Risk Analysis
Work related injury and disease arise from the hazards at work. These can include the design of work processes, the use of materials, substances, machinery and equipment - and the associated hazards (noise, fumes, radiation, etc), and the organisation of work.
Working hours should be treated in the same way as other safety and health hazards. The first step in risk analysis is identification of the hazards. Techniques that can be used to identify hazards associated with hours of work arrangements may include:
- Conducting employee surveys
- Examining accident and sickness records
- Environmental and medical monitoring
- Assessing expert reports
- Reviewing current research literature
- Incident, injury and illness investigation
- Monitoring of accidents and incidents associated with travel to or from work.
- Investigating employee complaints
Factors to consider when determining the exposure, probability and consequences to analyse the risks posed by the identified hazards include:
- Type of work and workload of employees
- Competence of employees
- Special circumstances on the site
- Roster design including hours worked in any one period rest within and between work periods design principles for schedules
- Exposure standards
4.1.1 Workload
All jobs, and all tasks within jobs, impose a workload. The following need to be considered in analysis of risks for hours of work arrangements:
- the physical effort required eg. lifting, carrying, driving, operating a machine, using a keyboard
- the demands caused by monotonous, repetitive activities or the need for high vigilance and concentration
- the pressure on the employee, eg tasks required to be done
- the hours of work including night shift versus day shift, length of shifts, timing of shifts, and breaks between shifts
- the body’s physiological and psychological responses to workload, eg. heart rate, hormone production, blood pressure, stress, anxiety and fatigue;
- Physically or mentally demanding work will increase the risks associated with shift work and extended hours
4.1.2 Needs of Employees
Arrangements for hours of work should consider the needs, commitments and responsibilities for all employees who are trying to balance work and other commitments.
4.2 Risk Assessment
Risk assessment is a process to determine the likelihood of potential injury or illness for those exposed to the hazard. The risk assessment should consider any controls or methods already being used to control risk and assess the effectiveness of such current methods. Risk assessment methods should be identified that are appropriate for the hazards identified and may include:
- use of specialist expertise in scheduling and shiftwork
- use of techniques that enable calculation of potential sleep deprivation and fatigue risk factors
- consultation with staff on “best fit” schedules and on individual orientation to different work schedules
- use of available research on shiftwork
4.3 Risk Control
Where shift work is necessary, the risks can be reduced and controlled as risks associated with other hazards can be reduced and controlled. The factors to be considered include the following:
4.3.1 Length of shifts and working hours
Length of shifts, working hours and roster design need to take into account the site requirements and the requirement to maintain a safe and healthy workplace. Strategies that may assist in managing the risks associated with length of shift and working hours include:
- Where practical, scheduling complex tasks to be undertaken during the day.
- Rotating workers through different jobs to relieve the monotony of some tasks.
- Minimising or redesigning routine administrative tasks to ensure employees can focus on core duties during their night work.
- The allocation of employees during peak times and demands is fundamental in minimising the exposure to risks associated with extended working hours. Numbers and types of employees should be rostered on the basis of predictable demands for services.
- Replacing or substituting employees where extended hours have created a risk to safety and health.
- Deferring non-urgent work to allow appropriate rest and recuperation for employees.
4.3.2 Split or broken shifts
Split or broken shifts should be avoided if possible. Particular attention to risk management should be ensured if split or broken shifts are required. As they are usually arranged to cover periods of peak activity, they put employees at greater risk of work overload.
4.3.3 Overtime
Overtime should not extend the length of shifts beyond the maximum lengths established at the mine.The overall work pattern when overtime shifts are introduced should be monitored. Records should be kept of the hours individual employees have worked. Employers need to establish systems that provide for relief staff to cover emergencies, or possible absences on incoming crews.
4.3.4 Night Work
Work that is physically or mentally demanding, monotonous, or requires high vigilance can lead to fatigue which may be made worse by night work. and this needs to be considered when designing rosters. Night work should be organised to allow and encourage employees to take additional breaks and pauses. Breaks before the onset of fatigue are much more beneficial than those taken after the onset of fatigue.
4.3.5 Extended shifts
There is the definite possibility of increased hazards associated with extended shifts and in order to minimise the hazards, it is essential that the increased leisure time be used for recuperation and recreation and not as an opportunity for additional employment.
4.3.6 Breaks during shifts
Adequate and regular rest breaks and pauses are necessary if risk to safety and health is to be properly controlled. Meal breaks or rest breaks should not be traded off for an early finish time. The number and duration of breaks during a shift should be adapted to the type of work, workload and length of shift. The longer the shift, the longer the total break time required per shift and regular rest breaks and pauses are needed. Some flexibility to enable workers to take a break when fatigued should be allowed where possible. Considerable research has been undertaken on this subject and suggested readings are provided in the references.
4.3.7 Rest days
Good roster design should take into account the need for adequate blocks of rest days to allow for recovery.
4.3.8 Employee responsibilities
It is the responsibility of the employee to ensure they make appropriate use of rest periods and are fit for duty. Factors that may diminish the effectiveness of rest periods include:
- moonlighting
- medication
- other leisure activities
The employee should notify the supervisor of any impairment or potential impairment that may place any person at risk prior to undertaking activities. Any risk assessment should include personal health and lifestyle factors.
4.3.9 Timing of shifts
It is recommended that shifts do not start between midnight and 6 am. This is to ensure an opportunity for adequate night rest.
4.3.10 Rotating shifts
If a rotating three shift system is in operation (day, afternoon and night), the preferred rotation should be in the order of day then afternoon then night. This is a forward rotation (as in forward on the clock face). If shift start times vary throughout a sequence of shifts, they should commence with an early start and move progressively later. Changes from a late start to an early start reduce the number of rest hours between shifts.
4.3.11 Roster pattern and length of cycle
When designing a roster, particular consideration should be given to:
- The number of consecutive day shifts
- The number of consecutive night shifts
- The length of the roster cycle
- The recovery time at the end of each roster cycle
- The recovery time from the end of each shift to the start of the next shift
It is generally preferable that the roster cycle be as short as possible. Rosters should be regular and predictable to avoid disruptions to rest and sleep periods, and for better organisation of private, family and social life. Roster details should be available to employees well in advance, and maximum notice should be given regarding changes in the roster.
4.3.12 Standby and on-call duties
Being on standby or on-call means that the employee has not entirely stopped work. Anxieties and stresses related to the job are still experienced. Such periods should be included in workload calculations. If people on-call are called in to work, this can lead to accumulated fatigue, lack of sleep and severely disturbed sleep.
4.3.13 Exchange of shifts
Exchange of shifts for special reasons may be allowed, provided the change does not result in excessive daily or weekly hours for any employee. A supervisor should be responsible for monitoring the effect on individual roster patterns. Exchange of shifts should not occur if it results in two or more continuous shifts being worked (ie. no break between), or if recommended maximum hours are exceeded.
4.3.14 Exposure to other safety and health hazards
Extended hour shifts may increase the risk of health effects that are generally associated with work. Exposure to work hazards such as noise, heat and chemicals may be increased and must be carefully monitored. The increased exposure of employees over a 12 hour shift period to physical stressors such as noise and contaminants represents an increase over the traditional eight hour shift that may not simply be 1.5 times that for eight hours.
Models to be used for the calculation of exposure limits for workers working in excess of an eighthour shift period need to take into account the reduced recovery time after exposure to contaminants if extended shifts are being worked. It is fundamental to good work practice to adopt the “as low as reasonably achievable” (ALARA) principle and keep all exposures significantly below specified standards to allow for day-to-day variability and ensure that workers are not over exposed.
Expert advice on exposure levels should be sought where necessary. Some references are included at
the end of this paper. Manual handling hazards may also be increased by extended shifts, due to the cumulative effects of muscle fatigue, sprains and strains.
4.3.15 Isolated work
While working in isolation is not unique to shift work or night shift, special attention needs to be paid to working in isolation under this regime. Recognition should be taken of the consequence of error and hence in periods where error is more likely additional controls may be required.
4.3.16 Hot work
The effects of working in high temperatures during shift work or for extended hours should be considered.
4.3.17 Hand-over
Appropriate mechanisms should be in place to enable efficient and safe handover between shifts, and ensure new shifts are adequately informed about all issues that have arisen in the workplace.
4.3.18 Travel
Travel to and from work can effectively extend the working hours and decrease the recovery time. Both employers and employees need to be aware of this. Travel between work locations is particularly relevant to contractors. For fly in/fly out operations, consideration needs to be given to the first and last shifts due to the
extended travel time at the start and end of the roster period.
4.3.19 Communication
Communication sessions should be considered as working. When organising communication sessions, care should be taken that participation does not require employees to work in excess of the site established maximum hours. Important communication sessions should be schedules to allow effective communication.
4.3.20 Information and education for workers and management
Employees should be provided with information on shiftwork including:
- The hazards associated with shiftwork, including extended hours and roster patterns
- Potential safety and health impacts of shiftwork
- How to identify potential and/or existing problems associated with lack of sleep and fatigue
- Individual coping strategies to best minimise the adverse impacts of shiftwork
- Services made available to assist employees to cope with shiftwork
-. The effects of diet and exercise on the ability to cope with shiftwork;
-. The effects of drugs and alcohol on the ability to cope with shiftwork.
Provision of training and advice would include managers and supervisors who should be fully educated about shiftwork occupational safety and health issues. Management needs to update policies to reflect current legislative requirements and scientifically based approaches to shiftwork management. Promotion of good shiftwork and workplace practices needs to be adopted by management with the provision of adequate and appropriate resources.
Special arrangements should be made to allow shift workers access to training and information. Training should be organised so it is available to employees on all shifts. If shift workers must attend training outside their shift, they should be considered to be at work and rosters should be adjusted accordingly.
4.3.21 Heating and cooling
Ambient temperature levels should be considered when designing roster systems to determine what if any additional controls are necessary to control risk.
4.3.22 Commuter operations
Satisfactory management of risks to safety and health associated with hours of work arrangements and extended shift rosters for fly in/fly out and drive in/drive out operations may be improved by:
- The provision of full information to prospective employees regarding geographical location, workplace and living conditions on-site.
- A recognition that personal problems both onsite and off-site can adversely affect safety and health.
- Provision of adequate recovery time between periods on-site for emotional, physical and social adjustment.
- The establishment of a shift changeover process to fully acquaint incoming workers with current mining conditions.
- The provision of a good standard of on-site accommodation for workers including contractor’s employees where site accommodation is required.
- The provision of a range of recreational facilities together with encouragement to use the facilities.
- The provision of adequate health care facilities on site for all workers accessible at all hours.
- The scheduling of regular consultation with the workforce on existing arrangements and proposals for change.
- The encouragement of workers to prepare themselves physically and mentally for return to work following rest and recuperation.
4.3.23 Audit and Review
The risk management of hours of work arrangements should be audited and reviewed at intervals as appropriate to ensure the continuing suitability, adequacy and effectiveness of the control of the associated risks. The need for audit and review may be indicated by changing circumstances at the mine, changes to rostering patterns or other indications that risks are not controlled.
5. COMPLIANCE WITH OBLIGATIONS UNDER MINING SAFETY AND HEALTH LEGISLATION
Employers and employees should be conversant with their respective responsibilities, which are defined in the mining safety and health legislation. This paper operates in the context of mining safety and health legislation for Queensland that sets out obligations for employers, employees and others to ensure the risk of injury or illness resulting from mining operations is at an acceptable level.
Hours of work arrangements, compressed shift schedules and commuter operations require all parties to focus on their respective responsibilities to ensure that an acceptable level of risk is maintained at all mining operations.