Course:SPPH381B/TermProject/Mirrors - Rachael

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Introduction

Mirrors, an item often taken for granted, are found abundantly world wide. First being used through obsidian rock, a piece of volcanic glass more than 8, 000 years ago, mirrors have since progressed to the now traditional silvered-glass mirror, which requires a glass base with a metal coating (Wikipedia 2017). While this has recreational and scientific benefits - the production of this material also has occupational concerns. This project will explore the life-cycle of mirrors through highlighting the process steps involved. Of these, risk assessments will occur, with the associated hazards identified. Finally, this will be reviewed within the occupational hygiene paradigm before further improvements will be suggested. But first, one must understand what a mirror is comprised of.

Life-cycle

The life-cycle of a mirror begins with the resource extraction of all raw materials. These materials include silica, limestone, dolomite, tin, silver and copper - which are all extracted through the step of milling and mining. This resource extraction occurs through the use of fossil fuels. Following this, the materials are then transported to factories for the primary manufacturing step.

As glass is needed to form the base of a mirror, the primary manufacturing step involves using silica, limestone, dolomite and recycled glass to make glass sheets. Once this is completed, the glass sheets are often then transported to a separate factory for the secondary manufacturing step of mirror making. In this step, tin, silver and copper are applied to create the reflectivity required. Both of these steps rely on infrastructure to allow transportation, as well as power to allow the multitude of machines involved to run. Once the production of the mirror is finalised, transport is again required to distribute the product to the various retailers.

Unfortunately, following the use of mirrors, they cannot be recycled due to the many chemicals added in the secondary manufacturing process. This results in the mirrors being disposed into landfills. Glass on the other hand, is readily recycled, and can be used in a plethora of new applications.

Process steps

The process steps in mirror manufacturing highlighted above are complex, and many. To further understanding, these will be explained in detail beginning with the mining and milling process.

As stated, mining and milling is necessary to complete resource extraction of the raw materials (Design Life-Cycle 2017). Mining is the act in which minerals are extracted from their natural environment and transported to a mill for beneficiation (Cralley & Cralley 1989). Milling follows afterwards, and is the process of separating the desired mineral from the waste and concentrating the mineral to usable form (Cralley & Cralley 1989). This process occurs for all of the materials involved in mirror manufacturing; silica, soda ash, dolamite, tin, copper and aluminium.

Following mining and milling, the raw materials are then loaded onto trains or trucks, and transported to factories for manufacturing. They are often transported in large quantities by railroad and segregated into separate storage facilities (Cralley & Cralley 1989). In the case of minor batches, they may be delivered in bag, barrel or other containers (Cralley & Cralley 1989).

Once the materials arrive at their respective factories, receiving and unloading takes place. The process of storage, weighing, conveying and mixing of the batch occurs, with the assistance of a mechanical vibrator to aid in material flow (Cralley & Cralley 1989). Storage involves placing the batch materials into appropriately sized silos, which feeds raw material to the batch mixing area (Cralley & Cralley 1989). The exit end of the silo directs the batch material to the weighing scales, with the assistance of vibrators or hammers (Cralley & Cralley 1989). To ensure quality and batch consistency, the weighing process must be precise (Cralley & Cralley 1989). Once weighed, the batch material is dumped onto a conveyor system, in which it is transported to a rotary mixer. Moisture is added, which then creates a homogeneous mix to be added to the furnace (Cralley & Cralley 1989)

The batch mix is placed in the furnace for the task of melting them, and producing the molten glass for forming. The tank is constructed using special refractory brick, in which temperatures reach approximately 1335 - 1665 degrees Celsius. The fuel used is either natural gas or oil.

Once melted, the batch is refined into molten glass - which, for the purpose of making a mirror - is then rolled, drawn, ground and floated to form the basic flat glass. Therefore, once the molten glass exits the tank, it s floated on a bath of molten tin to allow the bottom surface of the glass to form a smooth place (Cralley & Cralley 1989). The glass is rolled along the bath surface by pinch rolls, the speed of which determining the glass thickness (Cralley & Cralley 1989). This bath area requires 38 degrees Celsius, and the atmosphere is generally inert. The formed glass then goes through the annealing process, which controls the rate of cooling - to limit temperature stress of the glass, which if not relieved would cause the glass to fracture (Cralley & Cralley 1989). Thus, a lehr is used, in which the temperature is reduced from approximately 540 degrees Celsius to 21 degrees Celsius. Cooled air is required to complete this.

Once completed, the glass ribbon must be cut to size dependent on the desired function. This occurs by drawing a hard material across the glass surface with the proper amount of pressure; which can be performed by hand or machine (Cralley & Cralley 1989). Finally, once cut the glass is packed either by hand or machine, and transported to a mirror manufacturing factory.

Firstly, the glass is placed on a conveyor belt, powered by electricity to remove any residue or contaminants, which would reduce the quality of the final product (Design Life-Cycle 2017). Polishing occurs through the use of cerium oxide and hot deionized water (Design Life-Cycle 2017).

The remaining process of mirror making consists of applying liquefied tin to the glass as adhesion (Design Life-Cycle 2017). Following this, silver is sprayed or poured in liquid form onto the tin layer in addition to a chemical activator to cause reflectivity (Design Life-Cycle 2017; Cralley & Cralley 1989). This coating is then strengthened with copper, which is sprayed on, rinsed and heated to vaporize any moisture (Design Life-Cycle 2017). Two layers of paint are then added for protection, with the first layer heated to 70 degrees Celsius, and the second heated to 100 degrees Celsius.

Once the process of mirror fabrication is completed, it can be then cut, fitted and sent to private retailers, or shipped elsewhere for further decorating.

The final step of the life-cycle is the reduction of mirror as waste. As many chemical agents are added within the mirror making process, mirrors are unable to be recycled like glass. Thus, while recycled glass is reused for further product manufacturing, mirrors are sent to landfills. Through all of these processes, many individualized hazards can be identified.

Risk assessment

Within the process outlined, risk assessments of the following steps will occur; - Silica milling - Forklift operation - Receiving and unloading - Storage - Melting - Cutting - Silver spray/liquid form

Silica milling requires a risk assessment, due to the harmful nature of silica and combination of milling. Thus the potential hazards include; dust exposure (fine, concentrated silica particle inhalation), comminution accident (causing injury or accident by gyratory or jaw crushers) and radon exposure in varying concentrations or confined spaces (increased risk of cancer) (Cralley & Cralley 1989).

A forklift operation risk assessment must consider the following hazards; motor vehicle accident (causing injury and death), whole body vibration (causing low back pain) and impaired communication (loss of all senses, causing injury and death).

The receiving and unloading process requires a risk assessment of the associated hazards, which include; mechanical noise exposure (hearing damage), sedentary behaviour (obesity, cardiovascular disease) and ergonomics (manual labour involving repeated body movements).

The storage of materials process also requires a risk assessment to highlight hazards involved; maintenance and repair (raw material exposure), exit from silo to weigh scale (dust emission), vibrator or hammer use (hearing damage).

The melting of batch materials ensues its own hazards, thus enticing a risk assessment of; chrome refractory brick material (human carcinogen), high temperature (dehydration, organ failure) and use of combustion blowers, fuel feeds and auxiliary equipment (hearing damage).

The cutting of glass requires a risk assessment, to explore the following potential hazards; extreme applied pressure (built up energy, may cause injury), disposal of scrap glass (hearing damage), and ergonomics (repeated body movement, causing strain and injury).

The spraying or concealing of liquid form of silver also requires a risk assessment, with the following potential hazards identified; silver spray exposure (airborne levels of hazardous material), silver spray contamination in water (pollutant consumed), and byproducts of metallic oxide formed (carcinogen).

Hazards

The following hazards will be explored for a comprehensive understanding of the dangers involved in the life-cycle of a mirror;

Process Silica mining Forklift operation Receiving and unloading Storage of materials Melting of batch materials Cutting of glass Spraying/ or concealing silver Hazard Dust exposure Sedentary behaviour Hearing impairment Machinery maintenance and repair High temperature Scrap glass disposal Silver spray exposure

Occupational Hygiene Paradigm

Brief para

Silica dust exposure

Silica is one of the most common minerals on earth and the major ingredient in glass, which is used to manufacture mirrors (Poinen-Rughooputh et al 2016). Silica exposure occurs mainly in mining areas for metals and coal, as well as manufacturing of building materials (Poinen-Rughooputh et al 2016). The mechanical breakdown of quartz-containing silica releases large amounts of dust in the workplace, in addition to the transportation of dusty raw materials, and in storage rooms where dust is settled (WHO 2014). The International Standard Organization (ISO) state that dust is a small solid particle below 75 µm in diameter, which may be airborne for some time before settling out under their own weight (WHO 2014).

There are various factors affecting the severity of silica dust exposure, and these relate to particle size, but primarily airborne activity and route of exposure. The particle size of silica dusts depends on the method of breakdown of quartz. For example, in mining the mechanical breakdown includes grinding, cutting, drilling, crushing, explosion or increased friction of materials. More dust is generated when the energy associated with the process increases, e.g. a grinding wheel at higher speeds (WHO 2014). In this instance, primary airborne dust is generated, with the size of the particle dictating both the length of time it remains airborne, and the final deposition location of the particle (WHO 2014). Where the particle is finally deposited also depends on the route of exposure, either being through the skin, ingested, or by inhalation – with the latter being most severe (WHO 2014). The inhalation of dust and its associated effects are dependent on the type of dust and the exposure, which determines the dose. For example, breathing rate and volume affect the uptake, and thus dose of dust particles (WHO 2014). These factors within silica dust exposure may lead to serious illness or life-threatening conditions.

Silica dust exposure is related to various health risks, such as pneumoconiosis and cancer, and is also dependent on the route of exposure (WHO 2014). The dermal effects of silica dust exposure may lead to dermatoses or even skin cancer (WHO 2014). As silica dioxide is water soluble, skin absorption of the airborne particles may occur and cause systemic intoxication from entering through the bloodstream (WHO 2014). Inhalation of silica dust is the most potent, with silicosis widely known as a disease outcome, which involves scarring of the lungs with a cough and shortness of breath (CDC 1978). These diseases often have a longer latency period, which is often the case with pneumoconiosis (WHO 2014). Workers exposed to high air concentration of dust, for extended periods are the most susceptible to harmful health effects (WHO 2014). Therefore, exposure limitations have been set. The permissible exposure limit (PEL) for crystalline silica is 50 micrograms per cubic metre of air, averaged over an 8-hour shift (OSHA 2016). The amount of silica per cubic metre of air may be measured using gravimetric samplers, personalDataRAM’s (pDR), personal dust monitors (PDM) or pDR field calibrations (CDC 2010). These measurements, in addition to the use of PELs are vital in recognising and evaluating the hazard, however further controls are needed for protection of the workers.

In the process of mining, the first step in controlling exposure levels of crystalline silica dust typically include elimination methods. However, within mining, and for the raw materials that must be extracted for manufacturing of glass, crystalline silica cannot be eliminated, nor can it be substituted (WHO 2014). However, effective engineering controls include local exhaust ventilation, general dilution ventilation and isolating workers (CDC 1978). Within the process, wetting should occur – which involves applying water to a dust-filled location/process to minimise airborne activity and thus limit exposure (WHO 2014). Administration controls include regular training, maintenance, inspection of equipment, cleaning and evaluation (CDC 1978). The use of warning signs is also particularly important, to alert workers when they are entering a dust-hazardous zone (WHO 2014). The final, and necessary control method is using personal protective equipment, such as respirators (CDC 1978). However, the aim of the previous controls is to minimise the need and reliance on this final method of protection for workers (OSHA 2016). By implementation and adherence to these controls, exposure to crystalline silica is significantly reduced, and thus potentially life-threatening diseases are avoided (WHO 2014).

Sedentary behaviour

Sedentary behaviour from the Latin word, sedere means “to sit” and includes any waking activity with the energy expenditure of <1.5 METs (Owen et al. 2010). For example, to walk leisurely would expend 2.5 METs, whereas walking briskly would expend up to 5 METs (Wellsource 2008). Sedentary behaviour can occur in various settings such as watching television, sitting during transit or in the workplace. In Canada, approximately 69% of adults’ waking hours are spent sitting – about 9.7 hours each day (Colley et al. 2011). In the case of forklift operators, sedentary behaviour (sitting) is required at all times when using traditional forklift vehicles (Occupational Health and Safety Magazine 2002). While most people believe regular physical activity can negate periods spent sedentary, this is not so (Patel et al. 2010). Allowing time to take regular breaks may however mitigate the negative health effects of sedentary behaviour (Project Health 2017).

Sedentary behaviour is associated with many poor health outcomes. These include premature death, diabetes, osteoporosis, heart disease, high blood pressure, obesity and cancer (Tremblay et al. 2010; CSEP 2017). Additionally, workers who identified as being regularly sedentary reported feeling mentally and physically exhausted, stressed, depressed, and even socially isolated and trapped; which led to a loss of productivity and disengagement with daily tasks (Project Health 2017). To prevent these outcomes of sedentary behaviour, the Canadian Physical Activity Guidelines recommend that adults accumulate a minimum of 150 minutes of physical activity per week, in periods of 10 minutes or more (CSEP 2017). Results from a survey between 2007-2009 regarding physical activity of Canadian adults showed that approximately only 15% of adults met these guidelines on a regular basis (Colley et al. 2011). For an accurate representation of sedentary behaviour within forklift operators, measurements must be undertaken. Measurements for sedentary behaviour can be taken on a variety of levels, and can be either objective or subjective reports. For example, surveys may be taken from workers, via self-reports on their time spent sedentary. Additionally, objective measurements can be made by using accelerometers (Government of Canada 2015). However biological measurements can be made by documenting markers such as urine, blood samples, blood pressure and anthropometric measurements (Loprinzo et al. 2013).

As this hazard is also a behaviour, tangible exposure limits are difficult to ascertain. However, sedentary behaviour is said to occur in energy expenditures of < 1.5 METs, in addition to periods of thirty minutes and more – thus, avoiding these behaviours is primary (Dommelen et al. 2016). These behaviours may be avoided through occupational controls, beginning with elimination.

Elimination of sedentary behaviour is difficult to achieve when the use of forklifts is often necessary for the transportation of materials (Cralley & Cralley 1989). The use of other mechanisms and vehicles may be suggested, i.e. cranes, however this alternative would still require monitoring and its associated sedentary behaviour from a worker (Cralley & Cralley 1989). Substitution methods however provide more viable possibilities for reduced hazard exposuure. The image below illustrates the outline of a sedentary worker’s day timeline, from beginning to end of shift (Safe work Australia n.d.).

(Safe Work Australia n.d.)

It is evident here that substituting sitting time with standing or walking allows sedentary behaviour to be minimised, and prevented from reaching the thirty-minute danger time (Dommelen et al. 2016). However, there are challenges within this. These challenges include the nature of work tasks, i.e. high volume work load, and organisation aspects among blue-collar workers, meaning they have reduced autonomy to break up prolonged sedentary time (Gupta et al. 2016). Engineering controls within forklift operations may include acquiring vehicles that allow the option of either sitting or standing, as equivalent to the sit-stand desks now available (Gardner et al. 2016). This evokes benefits beyond reduction of sedentary behaviour; the line of sight (LOS) amongst operators is improved in addition to reduced risk of fatigue, and thus fewer accidents occur, and posture is aided and thus reduced musculoskeletal injuries are associated (Delgado 2012). Administrative controls for reducing sedentary behaviour may simply include educational programs, to bring awareness to workers about the prevalence and risks of sedentary behaviour (Gardner et al. 2016). This education may include encouraging workers to engage abdominal muscles whilst sitting, stretch legs whilst waiting, and seeking walking breaks when feasible (Delgado 2012). This hazard is rare, in that no personal protective equipment may reduce exposure to the hazard – apart from wearing clothing that is conducive to free-moving - thus it is vital the previous controls are sought after.

Hearing Impairment

Hearing impairment is a common occurrent within occupational settings, and is measured by the frequency and decibels (dB) from noise (WHO 2004). WHO defines hearing impairment as “permanent unaided hearing threshold level for the better ear of 41 dBHL or greater for the four frequencies 500, 1000, 2000 and 4000 kHz” (WHO 2004, p.8). In measuring the prevalence of workers exposed to high noise levels, beyond 90 dB(A) – a survey was undertaken in the USA in 1981, which included over 9 million production workers, and showed that 56% of workers were exposed to noise levels above 90 dB(A) (WHO 2004). Furthermore, the rate of hearing impairment differs within the various occupational settings. For example, industry-specific studies estimate that 70% of male metal/non-metal miners will incur hearing impairment by the age of 60 (NIOSH 1991). Hearing impairment, may progress into noise-induced hearing loss (NIHL) which is irreversible and increases in severity with repeated exposure (WHO 2004).

Associated consequences of NIHL include; social isolation, impaired communication with co-workers and family, decreased ability to monitor the worksite (i.e. warning signals and equipment sounds), increased injuries due to impaired communication and isolation, productivity loss, expenses for workers’ compensation and hearing aids, and anxiety, irritability and decreased self-esteem (WHO 2004). While occupational noise exposure is the major cause for hearing impairment in the workplace, workers may be increasingly susceptible due to biological or behavioural factors (Kurmis & Apps 2007). Previous surgery or infections may predispose workers to increased hearing loss, in addition to genetic factors and lastly cigarette smoking – which has been strongly associated with an increased frequency of hearing loss (Kurmis & Apps 2007). To protect against these factors, and prevent the potential progression of NIHL, the following Occupational Exposure Limits (OEL) exist.

OELs for noise are provided as the maximum duration of exposure permitted for various noise levels (CCOHS). The OELs depend on two key factors that are used to prepare exposure-duration tables: criterion level and the exchange rate, which can be seen in the table below (CCOHS). The table illustrates two different criterion levels, in addition to the two different exchange rates; 3 dB (A) and 5 dB (A). These numerical values represent the permitted duration of exposure following increased noise level. For example, if the allowable noise level increases by 3 dB (A), then the permitted duration is reduced by half (CCOHS).

(CCOHS 2017a)

The Canadian federal noise regulations permit 87 dB(A) for an eight-hour work shift (CCOHS 2017a). However, most jurisdictions permit 85 dB(A), with Quebec allowing 90 dB(A) (CCOHS 2017a). To assess occupational noise levels, the following measures are used; sound pressure level, sound level and equivalent sound levels (CCOHS 2017a). The most commonly used instruments for measuring noise include the sound level meter (SLM), the integrating sound level meter (ISLM) and the noise dosimeter (CCOHS 2014). The appropriate use of both the OELs and measures aim to effectively protect workers, however controls are needed for maximum effectiveness.

With respect to the previously mentioned hierarchy of control, elimination of hazard must be the first step undertaken, followed by substitution, engineering controls, and personal protective equipment (). In the receiving and unloading stage of manufacturing, elimination of noise is difficult due to materials needing to be transported to and within the factory (Design Life-Cycle 2017). Cralley and Cralley (1989) suggest that materials are often unloaded into separate storage facilities which is an exemplified method of elimination, however this noise avoidance is not always achievable. For example, the railroad car or dump truck vibrator required, can produce noise exceeding 95 dB(A) (Cralley & Cralley 1989).

Methods for substitution however pose various viable options, including: enclosing or shielding noisy equipment, maintaining and repairing equipment, mounting noisy equipment on special surfaces to reduce vibration and the installation of silencers, mufflers, or baffles (OSHA 2017). Additionally, the employee should be removed from noise exposure by isolating them in an enclosure with controls to monitor the process, that is both conditioned and soundproofed – to protect from all harmful noise (Cralley & Cralley 1989). Engineering controls are necessary and include treating floors, ceilings and walls with acoustical material that reduces both the reflection and reverberation of noises (OSHA 2017). In addition, sounds barriers may be erected at adjacent work stations to mitigate noise created (OSHA 2017).

To improve the effectiveness of the above controls, workers must be met with administrative controls such as education, time limits and warning signs regarding the workplace and noise exposure. Education may include learning how to use quiet work methods instead of noisy ones (OSHA 2017). To prevent extended exposures, employer’s may limit workers’ time in noisy locations (OSHA 2017). In locations expecting high noise levels, warning sings should be erected to encourage workers to exercise caution, and if needed, resort to personal protective equipment (Cralley & Cralley 1989). This PPE would include appropriate hearing protection for the noise level, and must be met with PPE program, so that workers are correctly using the equipment and final control (Cralley & Cralley 1989).

High temperature

Silver spray exposure

Scrap glass/mirror disposal

Conclusion

Life-cycle of mirrors is multifaceted and due to the hazards identified, deserving of detail.

Important to note the issue of recycling. Further suggestions for mitigating this issue are required, such as seeking alternative materials in constructing mirrors. Also must be aware that while manufacturing occurs mainly within factories, some independent retail stores do complete their own mirror cutting and shaping. This creates its own associated issues, which must not be overlooked.

References

Davies, H 2017, Lecture 4, PowerPoint Slides, University of British Columbia, Vancouver. Harraz, H 2015, Silica sand and glass industry, PowerPoint slides, SlideShare, viewed 15 February 2016, <http://www.slideshare.net/hzharraz/silica-sand-and-glass-industry>. Recycle Nation 2016, How to Recycle Mirrors, viewed 15 February 2016, <http://recyclenation.com/2015/08/how-to-recycle-mirrors>. Wikipedia 2017, Mirror, viewed 14 February 2017, <https://en.wikipedia.org/wiki/Mirror>. MadeHow 2017, Mirror¸ viewed 14 February 2017, <http://www.madehow.com/Volume-1/Mirror.html>.