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A large cadre of highly trained engineers develop and refine the structural characteristics of the aircraft or space vehicle. Additional engineers characterize the strength and durability of component materials and develop effective manufacturing processes. Computers have taken on much of the calculating and drafting work that was previously performed by engineers, drafters and technicians. Integrated computer systems can now be used to design aircraft without the aid of paper drawings or structural mock-ups. Manufacturing begins with fabrication: the making of parts from stock materials.

Fabrication includes tool and jig making, sheet-metal working, machining, plastic and composite working and support activities. Tools are built as templates and work surfaces on which to construct metal or composite parts. Jigs guide cutting, drilling and assembly. Fuselage sub-sections, door panels and wing and tail skins outer surfaces are typically formed from aluminium sheets that are precisely shaped, cut and chemically treated. Machine operations are often computer controlled. Huge rail-mounted mills machine wing spars from single aluminium forgings. Smaller parts are precisely cut and shaped on mills, lathes and grinders.

Ducting is formed from sheet metal or composites. Interior components, including flooring, are typically formed from composites or laminates of thin but rigid outer layers over a honeycomb interior. Composite materials are laid up put into carefully arranged and shaped overlapping layers by hand or machine and then cured in an oven or autoclave.

Assembly begins with the build-up of component parts into sub-assemblies. Major sub-assemblies include wings, stabilizers, fuselage sections, landing gear, doors and interior components. Wing assembly is particularly intensive, requiring a large number of holes to be precisely drilled and counter-sunk in the skins, through which rivets are later driven. The finished wing is cleaned and sealed from the inside to ensure a leak-proof fuel compartment.

The assembly line comprises several sequential positions where the airframe remains for several days to more than a week while predetermined functions are performed. Numerous assembly operations take place simultaneously at each position, creating the potential for cross exposures to chemicals. Parts and sub-assemblies are moved on dollies, custom-built carriers and by overhead crane to the appropriate position. The airframe is moved between positions by overhead crane until the landing and nose gear are installed.

Subsequent movements are made by towing. During final assembly, the fuselage sections are riveted together around a supporting structure. Floor beams and stringers are installed and the interior coated with a corrosion-inhibiting compound. Fore and aft fuselage sections are joined to the wings and wing stub a box-like structure that serves as a main fuel tank and the structural center of the aircraft. The fuselage interior is covered with blankets of fibreglass insulation, electrical wiring and air ducts are installed and interior surfaces are covered with decorative panelling.

Storage bins, typically with integrated passenger lights and emergency oxygen supplies, are then installed. Pre-assembled seating, galleys and lavatories are moved by hand and secured to floor tracks, permitting the rapid reconfiguration of the passenger cabin to conform to air carrier needs.

Powerplants and landing and nose gear are mounted, and avionic components are installed. The functioning of all components is thoroughly tested prior to towing the completed aircraft to a separate, well-ventilated paint hanger, where a protective primer coat normally zinc-chromate based is applied, followed by a decorative top-coat of urethane or epoxy paint. Prior to delivery the aircraft is put through a rigorous series of ground and flight tests. In addition to workers engaged in the actual engineering and manufacturing processes, many employees are engaged in planning, tracking and inspecting work and expediting the movement of parts and tools.

Craftspeople maintain power tools and reface cutting bits. Large staffs are needed for building maintenance, janitorial services and ground vehicle operation. The health and safety programmes tended to be highly structured, with the company executives directing health and safety programmes and a hierarchical structure reflective of the traditional command and control management system. The large aircraft and aerospace companies have staffs of safety and health professionals industrial hygienists, health physicists, safety engineers, nurses, physicians and technicians that work with line management to address the various safety risks that are found within their manufacturing processes.

This approach to line control safety programmes, with the operational supervisor responsible for the daily management of risks, supported by a core group of safety and health professionals, was the primary model since the establishment of the industry. The introduction of detailed regulations in the early s in the United States caused a shift to a greater reliance on the safety and health professionals, not only for programme development, but also implementation and evaluation. This shift was a result of the technical nature of standards that were not readily understood and translated into the manufacturing processes.

The previously integrated line control safety management programmes lost some of their effectiveness when the complexity of regulations forced a greater reliance on the core safety and health professionals for all aspects of the safety programmes and took some of the responsibility and accountability away from line management. With the increasing emphasis on total quality management throughout the world, the emphasis is again being placed back on the manufacturing shop floor. Airframe manufacturers are moving to programmes that incorporate safety as an integral component of a reliable manufacturing process.

All of the above systems are leading to a positive safety culture, which is leadership driven, with extensive employee involvement in both the process design and process improvement efforts. A substantial number of potentially serious hazards can be encountered in the airframe manufacturing industry largely because of the sheer physical size and complexity of the products produced and the diverse and changing array of manufacturing and assembly processes utilized. Inadvertent or inadequately controlled exposure to these hazards can produce immediate, serious injuries.

Immediate, direct trauma can result from dropped rivet bucking bars or other falling objects; tripping on irregular, slippery or littered work surfaces; falling from overhead crane catwalks, ladders, aerostands and major assembly jigs; touching ungrounded electrical equipment, heated metal objects and concentrated chemical solutions; contact with knives, drill bits and router blades; hair, hand or clothes entanglement or entrapment in milling machines, lathes and punch presses; flying chips, particles and slag from drilling, grinding and welding; and contusions and cuts from bumping against parts and components of the airframe during the manufacturing process.

The injuries and illnesses related to ergonomically related risks have mirrored the growing concern shared by all manufacturing and service-based industries. The airframe manufacturers have a long history in the use of human factors in developing critical systems on their product. The industry has processes that involve forceful exertions, awkward postures, repetitiveness, mechanical contact stress and vibration.

These exposures can be exacerbated by work in confined areas such as wing interiors and fuel cells. In the airframe industry some of the key ergonomic concerns are the wire shops, which require many hand tools to strip or crimp and require strong grip forces. Most are being replaced by pneumatic tools that are suspended by balancers if they are heavy. Height-adjustable workstations to accommodate males and females provide options to sit or stand.

Work has been organized into cells in which each worker performs a variety of tasks to reduce fatigue of any particular muscle group. In the winglines, another key area, padding of tooling, parts or workers is necessary to reduce mechanical contact stress in confined areas. Also in the wingline, height-adjustable work platforms are utilized instead of stepladders to minimize falls and place workers in neutral posture to drill or rivet. Riveters are still a major area of challenge, as they represent both a vibration and forceful exertion risk.

To address this, low-recoil riveters and electromagnetic riveting are being introduced, but due both to some of the performance criteria of the products and also the practical limitations of these techniques in some aspects of the manufacturing process, they are not universal solutions. With the introduction of composite materials both for weight and performance considerations, hand lay-up of composite material has also introduced potential ergonomic risks due to the extensive use of hands for forming, cutting and working the material.

Additional tools with varying grip size, and some automated processes, are being introduced to reduce the risks. Also, adjustable tooling is being used to place the work in neutral posture positions. The assembly processes bring about an extensive number of awkward postures and manual handling challenges that are often addressed by the participatory ergonomics processes. Risk reductions are achieved by increased use of mechanical lifting devices where feasible, re-sequencing of work, as well as establishing other process improvements that typically not only address the ergonomic risks, but also improve productivity and product quality.

These aircraft vary in size but some e. Due to the size of the aircraft, certain operations require personnel to work while elevated above the floor or ground surface. There are many potential fall situations within both aircraft manufacturing and maintenance operations throughout the air transport industry.

While each situation is unique and may require a different solution for protection, the preferred method of fall protection is by preventing falls through an aggressive plan for hazard identification and control. Effective fall protection involves an institutional commitment addressing every aspect of hazard identification and control.

Each operator must continually evaluate its operation for specific fall exposures and develop a protection plan comprehensive enough to address each exposure throughout their operation. Any time an individual is elevated they have the potential to fall to a lower level. Falls from elevations often result in serious injuries or fatalities. For this reason, regulations, standards and policies have been developed to assist companies in addressing the fall hazards throughout their operations. A fall hazard exposure consists of any situation in which an individual is working from an elevated surface where that surface is several feet above the next level down.

Assessing the operation for these exposures involves identifying all areas or tasks where it is possible that individuals are exposed to elevated work surfaces. A good source of information is injury and illness records labour statistics, insurance logs, safety records, medical records and so on ; however, it is important to look further than historical events.

Each work area or process must be evaluated to determine whether there are any instances where the process or task requires the individual to work from a surface or area that is elevated several feet above the next lower surface. Virtually any manufacturing or maintenance task performed on one of these aircraft has the potential to expose personnel to fall hazards because of the size of the aircraft.

These aircraft are so large that virtually every area of the entire aircraft is several feet above ground level. Although this provides many specific situations where personnel could be exposed to fall hazards, all the situations may be categorized as either work from platforms or work from aircraft surfaces. The division between these two categories originates with the factors involved in addressing the exposures themselves. The work-from-platforms category involves personnel using a platform or stand to access the aircraft.

It includes any work performed from a non-aircraft surface that is specifically used to access the aircraft. Tasks performed from aircraft docking systems, wing platforms, engine stands, lift trucks and so on would all be in this category. Potential fall exposures from surfaces in this category may be addressed with traditional fall-protection systems or a variety of guidelines that are currently in existence.

The work from aircraft surfaces category involves personnel using the aircraft surface itself as the platform for access. It includes any work performed from an actual aircraft surface such as wings, horizontal stabilizers, fuselages, engines and engine pylons. Potential fall exposures from surfaces in this category are very diverse depending on the specific maintenance task and sometimes require non-conventional approaches for protection.

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The reason for the distinction between these two categories becomes clear when attempting to implement protective measures. Protective measures are those steps that are taken to eliminate or control each fall exposure. The methods for controlling fall hazards may be engineering controls, personal protective equipment PPE or procedural controls. Some examples of engineering controls are railings, walls or similar area reconstruction. Engineering controls are the preferred method for protecting personnel from fall exposures. Engineering controls are the most common measure employed for platforms in both manufacturing and maintenance.

They usually consist of standard railings; however, any barrier on all open sides of a platform effectively protects personnel from the fall exposure. If the platform were positioned right next to the aircraft, as is common, the side next to the aircraft would not need rails, as protection is provided by the aircraft itself.

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The exposures to be managed are then limited to gaps between the platform and the aircraft. The controls themselves prove inefficient when designed to protect the perimeter of an aircraft surface, as they have to be specific to the aircraft type, area and location and must be positioned without causing damage to the aircraft. Engineering controls are used extensively during manufacturing processes from aircraft surfaces.

They are effective during manufacturing because the processes occur in the same location with the aircraft surface in the same position every time, so the controls may be customized to that location and position. An alternative to railings for engineering controls involves netting positioned around the platform or aircraft surface to catch individuals when they fall.

Figure 1. Boeing portable rail system; a two-sided guardrail system attaches to side of aircraft body, providing fallprotection during work on over-wing door and wing roof area. PPE for falls consists of a full body harness with a lanyard attached to either a lifeline or other suitable anchorage. These systems are typically used for fall arrest; however, they may also be used in a fall restraint system. Used in a personal fall arrest system PFAS , PPE may be an effective means for preventing an individual from impacting the next lower level during a fall.

To be effective, the anticipated fall distance must not exceed the distance to the lower level. It is important to note that with such a system the individual may still experience injuries as a result of the fall arrest itself. PFASs are used with work from platforms most often when engineering controls are not functional—usually due to restriction of the work process. They are also used with work from aircraft surfaces because of the logistical difficulties associated with engineering controls. The most challenging aspects of PFASs and aircraft surface work are the fall distance with respect to personnel mobility and the added weight to the aircraft structure to support the system.

The weight issue may be eliminated by designing the system to attach to the facility around the aircraft surface, rather than the aircraft structure; however, this also limits fall protection capability to that one facility location. PFASs are used more extensively in maintenance operations than manufacturing, but are used during certain manufacturing situations. A fall restraint system FRS is a system designed so that the individual is prevented from falling over the edge.

FRSs are the preferred evolution of PPE systems for both manufacturing and maintenance operations, because they prevent any fall-related injury and they eliminate the need for a rescue process. They are not extensively used in either work from platforms or aircraft surfaces, because of the challenges of designing the system so that personnel have the mobility needed to perform the work process, but are restricted from reaching the edge of the surface. At the time of printing, only one aircraft type the Boeing had an airframe-based FRS available.

See figure 3 and figure 4. A horizontal lifeline attaches to permanent fittings on the wing surface, creating six fall protection zones. Employees connect a 1. The system allows access only to the edge of the wing, preventing the possibility of falling from the wing surface. Procedural controls are used when both engineering controls and PPE are either ineffective or impractical. This is the least preferred method of protection, but is effective if managed properly.

Procedural controls consist of designating the work surface as a restricted area for only those individuals that are required to enter during that specific maintenance process. Fall protection is achieved through very aggressive written procedures covering hazard exposure identification, communication and individual actions. These procedures mitigate the exposure as best as possible under the circumstances of the situation. They must be site specific and must address the specific hazards of that situation.

These are very seldom used for work from platforms in either manufacturing or maintenance, but they are used for maintenance work from aircraft surfaces. The manufacture of aircraft engines, whether piston or jet, involves the conversion of raw materials into extremely reliable precision machines. The highly stressed operating environments associated with air transport require the use of a broad range of high-strength materials. Both conventional and unique manufacturing methods are utilized. Aircraft engines are primarily constructed of metallic components, although recent years have seen the introduction of plastic composites for certain parts.

Air pollution – a major global public health issue

Various aluminium and titanium alloys are used where strength and light weight are of primary importance structural components, compressor sections, engine frames. Chromium, nickel and cobalt alloys are used where resistance to high temperature and corrosion are required combustor and turbine sections. Numerous steel alloys are used in intermediate locations. Since weight minimization on aircraft is a critical factor in reducing life-cycle costs maximizing payload, minimizing fuel consumption , advanced composite materials have recently been introduced as light-weight replacements for aluminium, titanium and some steel alloys in structural parts and ductwork where high temperatures are not experienced.

These composites consist primarily of polyimide, epoxy and other resin systems, reinforced with woven fibreglass or graphite fibres. Virtually every common metalworking and machining operation is used in aircraft engine manufacture. This includes hot forging airfoils, compressor disks , casting structural components, engine frames , grinding, broaching, turning, drilling, milling, shearing, sawing, threading, welding, brazing and others.

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Associated processes involve metal finishing anodizing, chromating and so on , electroplating, heat treating and thermal plasma, flame spraying. The high strength and hardness of the alloys used, combined with their complex shapes and precision tolerances, necessitate more challenging and rigorous machining requirements than other industries. Some of the more unique metalworking processes include chemical and electrochemical milling, electro-discharge machining, laser drilling and electron-beam welding.

Chemical and electrochemical milling involve the removal of metal from large surfaces in a manner which retains or creates a contour. The parts, depending upon their specific alloy, are placed in a highly concentrated controlled acid, caustic or electrolyte bath. Metal is removed by the chemical or electrochemical action. Chemical milling is often used after forging of airfoils to bring wall thicknesses into specification while maintaining the contour. Electro-discharge machining and laser drilling are typically used for making small-diameter holes and intricate contours in hard metals.

Many such holes are required in combustor and turbine components for cooling purposes. Metal removal is accomplished by high-frequency thermo-mechanical action of electro-spark discharges.

Air Pollution Modeling and its Application XV

The process is carried out in a dielectric mineral oil bath. The electrode serves as the reverse image of the desired cut. Electron-beam welding is used to join parts where deep weld penetration is required in hard-to-reach geometries. The weld is generated by a focused, accelerated beam of electrons within a vacuum chamber. The kinetic energy of the electrons striking the work-piece is transformed into heat for welding. With wet lay-up, the viscous uncured resin mixture is spread over a tooling form or mould by either spraying or brushing.

The fibre reinforcement material is manually laid into the resin. Additional resin is applied to obtain uniformity and contour with the tooling form. The completed lay-up is then cured in an autoclave under heat and pressure. Pre-impregnated materials consist of semi-rigid, ready-to-use, partially-cured sheets of resin-fibre composites.

The material is cut to size, manually moulded to the contours of the tooling form and cured in an autoclave. Cured parts are conventionally machined and assembled into the engine. In order to assure the reliability of aircraft engines, a number of inspection, testing and quality-control procedures are performed during the fabrication and on the final product. Common non-destructive inspection methods include radiographic, ultrasonic, magnetic particle and fluorescent penetrant. They are used to detect any cracks or internal flaws within the parts.

Assembled engines are usually tested in instrumented test cells prior to customer delivery. Health hazards associated with aircraft engine manufacture are primarily related to the toxicity of the materials used and their potential for exposure. Aluminium, titanium and iron are not considered significantly toxic, while chromium, nickel and cobalt are more problematic.

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Certain compounds and valence states of the latter three metals have indicated carcinogenic properties in humans and animals. Their metallic forms are generally not considered as toxic as their ionic forms, typically found in metal finishing baths and paint pigments.

In conventional machining, most operations are performed using coolants or cutting fluids which minimize the generation of airborne dust and fumes. With the exception of dry grinding, the metals usually do not present inhalation hazards, although there is concern about the inhalation of coolant mists. A fair amount of grinding is performed, particularly on jet engine parts, to blend contours and bring airfoils into their final dimensions.

Small, hand-held grinders are typically used. Where such grinding is performed on chromium-, nickel- or cobalt-based alloys, local ventilation is required. This includes down-draft tables and self-ventilating grinders. Dermatitis and noise are additional health hazards associated with conventional machining. Employees will have varying degrees of skin contact with coolants and cutting fluids in the course of fixing, inspecting and removing parts.

Repeated skin contact may manifest itself in various forms of dermatitis in some employees. Generally, protective gloves, barrier creams and proper hygiene will minimize such cases. High noise levels are often present when machining thin-walled, high-strength alloys, due to tool chatter and part vibration. This can be controlled to an extent through more rigid tooling, dampening materials, modifying machining parameters and maintaining sharp tools.

Otherwise, PPE e. Safety hazards associated with conventional machining operations mainly involve potential for physical injuries due to the point-of-operation, fixing and power transmission drive movements. Control is accomplished through such methods as fixed guards, interlocked access doors, light curtains, pressure-sensitive mats and employee training and awareness. Eye protection should always be used around machining operations for protection from flying chips, particles and splashes of coolants and cleaning solvents.

Metal-finishing operations, chemical milling, electrochemical milling and electroplating involve open surface tank exposures to concentrated acids, bases and electrolytes. Most of the baths contain high concentrations of dissolved metals. Depending upon bath operating conditions and composition concentration, temperature, agitation, size , most will require some form of local ventilation to control airborne levels of gases, vapours and mists.

Various lateral, slot-type hood designs are commonly used for control. The corrosive nature of these baths dictates the use of eye and skin protection splash goggles, face shields, gloves, aprons and so on when working around these tanks. Emergency eyewashes and showers must also be available for immediate use. Electron-beam welding and laser drilling present radiation hazards to workers. Electron-beam welding generates secondary x-ray radiation bremsstrahlung effect.

In a sense, the welding chamber constitutes an inefficient x-ray tube. It is critical that the chamber be constructed of material or contain shielding which will attenuate the radiation to the lowest practical levels. Lead shielding is often used. Radiation surveys should be periodically performed. Lasers present ocular and skin thermal hazards. Also, there is potential for exposure to the metal fumes produced by the evaporation of the base metal.

Beam hazards associated with laser operations should be isolated and contained, where possible, within interlocked chambers. A comprehensive programme should be rigorously followed. Local ventilation should be provided where metal fumes are generated. The major hazards related to the fabrication of composite plastic parts involve chemical exposure to unreacted resin components and solvents during wet lay-up operations. Of particular concern are aromatic amines used as reactants in polyimide resins and hardeners in epoxy resin systems.

A number of these compounds are confirmed or suspected human carcinogens.

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They also exhibit other toxic effects. The highly reactive nature of these resin systems, particularly epoxies, gives rise to skin and respiratory sensitization. Control of hazards during wet lay-up operations should include local ventilation and extensive use of personal protective equipment to prevent skin contact. Lay-up operations using pre-impregnated sheets usually do not present airborne exposures, but skin protection should be used.

Upon curing, these parts are relatively inert. They no longer present the hazards of their constituent reactants. Conventional machining of the parts, though, can produce nuisance dusts of an irritant nature, associated with the composite reinforcement materials fibreglass, graphite. Local ventilation of the machining operation is often required. Health hazards associated with test operations usually involve radiation x or gamma rays from radiographic inspection and noise from final product tests.

Radiographic operations should include a comprehensive radiation safety programme, complete with training, badge monitoring and periodic surveys. Radiographic inspection chambers should be designed with interlocked doors, operating lights, emergency shut-offs and proper shielding. Test areas or cells where assembled products are tested should be acoustically treated, particularly for jet engines.

Noise levels at the control consoles should be controlled to below 85 dBA. Provisions should also be made to prevent any build-up of exhaust gases, fuel vapours or solvents in the test area. In addition to the aforementioned hazards related to specific operations, there are several others worthy of note. They include exposure to cleaning solvents, paints, lead and welding operations. Cleaning solvents are used throughout manufacturing operations. There has been a recent trend away from the use of chlorinated and fluorinated solvents to aqueous, terpine, alcohol and mineral spirit types due to toxicity and ozone depletion effects.

Although the latter group may tend to be more environmentally acceptable, they often present fire hazards. Quantities of any flammable or combustible solvents should be limited in the workplace, used only from approved containers and with adequate fire protection in place. Lead is sometimes used in airfoil forging operations as a die lubricant. Many types of conventional welding are used in manufacturing operations. Metal fumes, ultraviolet radiation and ozone exposures need to be evaluated for such operations. The need for controls will depend upon the specific operating parameters and metals involved.

There is a growing market demand for the aerospace industry to decrease product development flow time while at the same time utilizing materials that meet increasingly stringent, and sometimes contradictory, performance criteria. Accelerated product testing and production may cause material and process development to outpace the parallel development of environmental health technologies. The result may be products which have been performance tested and approved but for which there exist insufficient data on health and environmental impact.

Regulations such as the Toxic Substance Control Act TSCA in the United States require 1 testing of new materials; 2 the development of prudent lab practices for research and development testing; 3 restrictions on the import and export of certain chemicals; and. The increased use of material safety data sheets MSDSs has helped provide health professionals with the information required to control chemical exposures.

However, complete toxicological data exist for only a few hundred of the thousands of materials in use, providing a challenge to industrial hygienists and toxicologists. To the extent feasible, local exhaust ventilation and other engineering controls should be used to control exposure, particularly when poorly understood chemicals or inadequately characterized contaminant generation rates are involved.

Respirators can play a secondary role when supported by a well-planned and rigorously enforced respiratory protection management programme. Respirators and other personal protective equipment must be selected to offer fully adequate protection without producing undue discomfort to workers. Oral presentation, bulletins, videos or other means of communication may be used.

The method of communication is important to the success of any workplace chemical introduction. In aerospace manufacturing areas, employees, materials and work processes change frequently. Hazard communication must therefore be a continuous process. Written communications are not likely to be effective in this environment without the support of more active methods such as crew meetings or video presentations. Provisions should always be made for responding to worker questions. Extremely complex chemical environments are characteristic of airframe manufacturing facilities, particularly assembly areas.

Intensive, responsive and well-planned industrial hygiene efforts are required to recognize and characterize hazards associated with the simultaneous or sequential presence of large numbers of chemicals, many of which may not have been adequately tested for health effects. The hygienist must be wary of contaminants released in physical forms not anticipated by the suppliers, and therefore not listed on MSDSs. For example, the repeated application and removal of strips of partially cured composite materials may release solvent-resin mixtures as an aerosol that will not be effectively measured using vapour-monitoring methods.

The concentration and combinations of chemicals may also be complex and highly variable. Delayed work performed out of normal sequence may result in hazardous materials being used without proper engineering controls or adequate personal protective measures. The variations in work practices between individuals and the size and configuration of different airframes may have a significant impact on exposures.

Variations in solvent exposures among individuals performing wing tank cleaning have exceeded two orders of magnitude, due in part to the effects of body size on the flow of dilution air in extremely confined areas. Potential hazards should be identified and characterized, and necessary controls implemented, before materials or processes enter the workplace. Safe usage standards must also be developed, established and documented with mandatory compliance before work begins. Where information is incomplete, it is appropriate to assume the highest reasonably expected risk and to provide appropriate protective measures.

Industrial hygiene surveys should be performed at regular and frequent intervals to ensure that controls are adequate and working reliably. Currently she acts as Director for the Center for Climate and Resilience Research CR2 , a center of excellence intended to deepen our understanding of climate system, its natural and anthropogenic changes and its consequences on society. Recently, she has been convened as lead author for the upcoming Intergovernmental Panel for Climate Change IPCC , in the chapter on short-lived climate forcers.

She teaches courses on atmospheric chemistry, modeling and global change, inverse modeling, atmospheric science and introductory physics at University of Chile. For parameters where sufficient data was not available values have been derived from the most recent effects-based water criteria including Provincial Water Quality Objectives and the Ontario Drinking Water Quality Standards as upper limits and Method Detection Limit as a lower limit.

These values are considered to be generally achievable in site situations typical of background while providing a level of human health and ecosystem protection consistent with background conditions and protective of sensitive ecosystems. The sediment standards in Table 1 are the same standards adverse effects-based developed for the Table 8 and 9 for properties within 30 m of a water body. These values are within the range of measured background sediment where data is available in the Sediment Guidelines and are considered to provide a level of human health and ecosystem protection consistent with background and protective of sensitive ecosystems.

Tables 6 and 7 are to be used in situations where there is less than 2 m of overburden above bedrock. They can also be used in situations where the QP is not satisfied that Tables 2 and 3 are suitable due to shallow depth to groundwater. Tables 6 and 7 were derived on the same basis as Tables 2 and 3 except that the calculation for dilution occurring in the aquifer is removed, and biodegradation between the groundwater and the basement is assumed to not be occurring.

Tables 8 and 9 are to be used where all or part of a property lies within 30 m of a surface water body. These standards were derived with the objective of protecting surface water bodies from movement of soil directly into surface water to become sediment, and assuming that there is no dilution in the groundwater for the aquatic protection pathway. The existence of any of the above conditions does not necessarily indicate that the generic criteria are not valid for a given site. There are many interrelated parameters and factors that were used in the development of the generic standards, and in many cases one factor, such as any of those above, can be outweighed by differences in other factors in a manner that, overall, there is sufficient natural protection provided by the site.

In addition, it must also be considered that the component that drives the standard may not be affected by the particular limiting condition described above e. The QP should consider these types of factors in assessing the appropriateness of the use of the generic standards.