1. Physical hazards, those involving forms of energy or having a mechanical or gravitational basis.
2. Chemical hazards, those produced through the action or reactions of chemical substances.
3. Biological hazards, those caused by living organisms or their products.
4. Psychological hazards, those related to stress, the emotional reaction to the environment, or interpersonal relations.

 Tables 18.1 and 18.2 in Chapter 18 present a more detailed classification with notes on the implications of these hazards. 

Hazards may be identified in many ways, the commonest of which are: 

1. Worker health complaints. A worker may present to the occupational health service with a disorder suspected to have been caused by a hazardous exposure. Since the ill effect has already taken place this is not the most desirable means of identifying a hazard. A harmful exposure may in fact have continued for months or years with the effects only lately becoming evidennt. (See Chapters 17 and 18. 
2. Literature, product descriptions, and MSDS information. Workers or supervisors may become aware of the presence of a hazardous substance in their workplace through information disseminated in the media or on a material safety data sheet (MSDS) provided by a supplier or by the employer. The MSDS can be a valuable source of information, not only for the worker, but also for the occupational health service. An example of an MSDS is provided Figure 23.1. MSDSs are required by law in the U.S. and Canada to contain information under the headings shown. 
3. "Walk-through" or site survey. This is the best method of finding hazards. Hazards can be searched out and identified before they affect workers. The search can be conducted periodically and systematically so that no major hazards will be missed. Site surveys will be discussed in detail. 

 The safety officer, occupational hygienist, occupational health nurse and the occupational physician are skilled in conducting site surveys to detect health and safety hazards. Each should be most knowledgeable in their own area of expertise but all should also be alert to hazardous conditions of any type present. An individual involved in a site survey should not ignore an obvious danger that falls outside their area of expertise. A safety officer, for example, on site to inspect the securing of compressed gas cylinders may notice, for example, that welders in the shop are producing a great amount of smoke and fumes which are hanging in the air but that the workers are not wearing respiratory protection. He or she should report these observations to the occupational hygienist, nurse or physician so that they can take appropriate action. Similarly, a nurse who observes workers using grinding tools without using eye protection should alert the safety specialist. 

Although site surveys are often conducted independently by members of the occupational health service, it is often preferable to use a team approach with a representative of each specialty area. The team approach is most appropriate when a worksite is visited for the first time or in connection with an investigation, an accident or incident. This is usually called a "health hazard evaluation" (HHE). It has the advantage of limiting the amount of disturbance to worksite operations as numerous visits over several days by assorted health or safety representatives can be disruptive. 

Form 23.1 specifies the information about the workforce at the site that should be sought before proceeding with an HHE. Before entering the worksite itself, the visitor should review the injury and the sickness absence records for the site in order to get a feel for the pattern of possibly work-related disorders.

The site visitors should have at least a basic understanding of the work operations carried out at the worksite. Not every detail of the work processes need be known, but participants should have sufficient understanding to be alert to the main potential hazards before setting out. There are many sources of information on worksite processes, some of which are included in the suggested library in Appendix 3. Sources of information specific to the plant include explanatory folders or brochures produced as part of the organization's public relations activity, engineering reports, interviews with site managers, and formal briefings by representative operational staff members. The information obtained should be recorded and kept for future reference by the occupational health service. 

From data obtained in advance about the workforce and the work processes, the site visitor should be able to anticipate the hazards likely to be encountered during the actual survey. One should consider each of the four major hazard categories while inspecting each workplace, following a mental check list. Table 23.1 presents an inventory of common exposures while Table 23.2 relates these common exposures to common industries in which they may be encountered. These tables are not replacements for more

Number of workers on site: Male Female

Age range of workers: _______ to ________ years.

Average age of workers: _______ years.

On-site Management: (names) (positions) (phone #)

On-site health and safety representatives:

(names) (positions) (phone #)

Table 23.1. Inventory of Exposures to Common Hazards

A. Aerosols, Irritants, and Gases E. Inorganic Dusts and Powders

Carbon monoxide Asbestos

Ethylene oxide Coal dust

Formaldehyde Fiberglass

Inert gases Silica

Hydrogen sulfide Talc

Nitrogen dioxide

Ozone

Phosgene

Sewer gas

Smoke

Sulphur dioxide

B. Biological Inhalants F. Insecticides and Herbicides

Bacteria Carbamates

Fungi Halogenated hydrocarbons

Molds Organophosphates

Organic dusts Phenoxyherbicides

Spores Natural products

Viruses

C. Corrosive Substances G. Radiation

Acids Infrared rays

Alkalis Laser beams

Ammonia Microwaves

Chlorine Radionuclides

Phenols Ultraviolet light

X-rays

Yellowcake

D. Dyes and Stains

Aniline dyes

Azo dyes

Benzidine

H. Metals and Metal Fumes L. Plastic and Polymer Constituents

Aluminum Acrylonitrile

Arsenic, arsine Aliphatic amines

Beryllium Epoxy resins

Cadmium Phthalates

Chromium Styrene

Cobalt Toulene diisocyanate

Iron Vinyl chloride

Lead

Mercury M. Welding Emissions

Nickel

Platinum salts

I. Organic Dust N. Solvents

Cotton dust Benzene

Poison oak n-Butanol

Carbon disulfide

Carbon tetrachloride

J. Petrochemicals Chloroform

Asphalt and tar Glycol ethers (cellusolves)

Creosote Ketones

PBB (polybrominated biphenyls) Methanol

PCB (polychlorinated biphenyls) Perchlorethylene

Petroleum distillates Toulene

Trichlorethan

Trichlorethylene

Cold stress

Heavy lifting

Noise

Thermal stress

Vibration

Agriculture/Farming/Pest control A, B, F, K, M

Automobile/Aircraft mfg. and repair A, C, E, H, K, M

Baking/Food handling B, L, M

Boiler operations and cleaning A, C, E, K

Carpentry/Woodworking/Lumber industry B. I, J, K,, N

Ceramics and masonry E, H

Chemical industry, biotechnology, A - N

and users of chemicals

Construction/Demolition/Road work/ C, D, E, K, J, M, N

Maintenance/Plastering

Dry cleaning/Laundry D, K, N

Electricity/Electronics A, C, E, H. J, N

Foundry work A, C, E, H, K, M, N

Health care/Laboratory work/Dental work A-E, G, J-L, N

Machinery/Grinding/Metalwork A, C, H, K, M, N

Mining A, E, G, K, M

Oil and gas/Petrochemical industry A, C, G, J, K, N

Paper industry E, H, N

Plastics manufacturing/Molding E, J, L

Plumbing/Pipefitting/Shipfitting A, C, E, H, K, M

Printing/Lithography D, K, N

Sandblasting/Spray painting A, E, H, K, N

Textile industry A, D, K, I, N

Transportation maintenance (shipyard/dockyard) A, C, E, H, J, K, N

Welding A, E, H, M

detailed descriptions of the processes and in the industry of concern but may be helpful in anticipating some hazards in the absence of more comprehensive descriptions.

While on site, the visitor should comply with all applicable safety procedures. The visitor should use appropriate safety equipment during the walk through, either bringing it along or making arrangements to obtain it at the site. Some managers feel that this may unduly alarm their employees and some occupational health professionals avoid doing so for fear of looking foolish and losing the respect of workers. Even so, there is no reason to jeopardize the health of those entrusted with the workers' health and visibly using personal

protection emphasizes the need to do so to workers at risk. A checklist of personal protection equipment that may be required is presented in Table 23.3. Certain personal items or grooming styles may be forbidden on site for safety reasons. These may include matches, lighters, contact lenses, beards/moustaches, loose hair, nylon garments, metal boot cleats or studs, leather soles, normal spectacle frames, coins, knives, firearms, jewelry, scarves, loose clothing, high-heeled shoes or boots, open-toed shoes, and running shoes. The visitor should always ask in advance and obtain permission or submit to special arrangements if any exceptions are to be made from these rules.

An important part of the on site survey is to confirm the availability of protective equipment to workers where they are needed. The protective equipment provided should be appropriate, in good repair, easily accessible, and modern. Once at the site, the visitor should first report his presence to the site manager and explain his intentions. This will provide the manager with an opportunity to inform the visitor of any deviations from normal work procedures that are underway or of any areas that are closed or "off limits" and will enable the visitor to ask any additional questions he may have about the workforce or operations. If any areas are designated off limits, the visitors should know why and what implications this may have for the site survey.

The visitors should be accompanied by a supervisor or a knowledgeable worker assigned by the supervisor during the first site survey, although on subsequent visits one may wish to proceed on one's own, with permission.

A notebook should be carried to capture information for later use. A cassette dictation recorder is useful for making notes but notebooks provide the advantage of allowing sketches of the floorplan or of equipment to be made. Use of a dictation machine may also be curtailed where loud noise is present. A 35-mm reflex camera may be used to record visual evidence of the working environment and as a future reference for recall. Permission should always be obtained before taking a camera onsite, however. There may be safety restrictions on the use of flash photography or security bans on photographing certain industrial processes. Capturing environmental working conditions on film using available light requires some

Head Protection: Hardhat, bump cap, helmet, cloth cap, hairnet, hood.

Eye Protection: Goggles (UV, IR, clear), safety glasses, face-shield.

Respiratory Protection: Dust mask, organic vapor mask, full-face cannister respirator,

emergency compressed air bottle supply respirator, respirator

spectacles.

Hearing Protection: Earplugs, earmuffs, acoustic helmet.

Hand Protection: Barrier cream, gloves, mitts, gauntlets.

Foot Protection: Safety boots or shoes, instep protectors, cleats,

insulated boots, ground shoe covers, rubbers.

Body Protection: Impervious suit, waterproof garment, apron,

heatproof suit, flameproof/resistant garment, jacket,

body armor, knee or elbow protection, wet suit.

photographic skill and equipment capable of meeting the demands. Notes should be made of the identity of each subject immediately after each shot is taken and the slides or prints should be labelled right after delivery to prevent the all too common problem of memory lapses.

The site survey should follow a logical sequence. This may be geographical, taking each building in turn, but whenever possible it is useful to follow the actual sequence of production. One starts at the point where raw materials are brought onto the site or are stored for use. From there, the walk-through should be made sequentially, observing each operation until the final finishing operation is carried out or the product leaves the site. The sequential approach should be followed if possible even if a particular process is being examined in isolation. The natural temptation is to head directly to the place of greatest hazard. This must be resisted if other significant hazards are not to be overlooked or missed because of time constraints.

All hazards identified should be noted along with the engineering controls and protective equipment that may be present. The site visitor should not be afraid to be curious or to ask any and all questions that will clarify the procedures before him. The visitor should not only observe, examine and note the condition of the protective equipment but should also question workers about their methods of work and their use of protective equipment in practice. Asking simple but direct questions of the workers regarding their opinions about specific job hazards and their own risk will provide insight as to their knowledge about the true potential effects of these hazards. When the visitor does not know the health effects of materials found in the workplace, the names and quantities of the materials should be recorded for later reference and investigation.

Workers expect answers from the plant nurse, hygienist or physician. The visitor should not be reluctant to express an opinion based on expert knowledge when asked. Not to express an opinion when asked conveys the message that the visitor considers current practices as satisfactory, even when they are not. Furthermore, workers are reassured when a health professional takes an interest in their work and their health> It is to the advantage of all to cultivate an interest in the work being done and an acquaintance with workers at the site. The next time the occupational health professional sees the worker, a relationship will be established allowing better appreciation of the work and the hazards faced.

In spite of this need for candor in answering questions, some discretion is needed. The prospects for producing change in a harmful work procedure or of eliminating a hazardous substance from a worksite should not be discussed with the individual worker when it is out of the direct control of the visitor. Such possibilities should always be presented first of all to the supervisor or manager of the operation. This will prevent embarrassment and the possibility of long-term ill-feeling toward the occupational health service.

Before leaving the site on completion of the survey, a brief visit should be made to the site supervisor. At this time, the principal findings might be discussed or this could be left until the manager is able to devote attention to the report. The visitor should always thank both the manager and the supervisor for the opportunity for the visit and for assistance given. Valuable relationships may be built in this way.

The solution of an occupational health problem at reasonable cost usually requires knowledge and technical resources beyond the capacity of the physician. Hazards in the workplace must first be identified, then evaluated, and finally controlled. This three-part function is the responsibility of two specially-trained occupational health professionals, occupational hygienists and safety engineers. Occupational hygienists deal mostly with problems of clinical exposure, ventilation, and plant processes. These professionals are usually on the staff of larger companies and are sometimes retained on a consulting basis by medium-sized companies. Small companies are frequently at a disadvantage in not having such expertise available. Engineers are more common in medium and smaller-sized industries and deal mostly with physical hazards, fire control, and safe work practices. A working knowledge of the available technical approaches is, however, useful and interesting to physicians dealing with occupational health problems. These technical approaches are summarized in Table 23.4.

The evaluation process requires experience with the particular industry and special monitoring instruments that test for the appropriate chemical and physical hazards. Some problems are simple to solve but many require extensive and costly changes in the plant structure and the manufacturing or production process. Selection and design of the best solution to the problem can be a highly technical challenge to the engineer and plant manager.

Often, this requires a drastic change to a complex technical process or work procedure, making complete elimination of the particular hazard unfeasible. The objective should then be to isolate the hazard to prevent workers from coming into contact with it. The basic approaches to controlling occupational hazards fall into five general categories: engineering, controls, containment and isolation, personal protection, administrative controls, and behavioral controls. There are variations on these approaches and numerous "tricks of the trade," but an understanding of these five basic approaches will help the physician understand what solutions may be proposed to a given occupational health problem.

Engineering Controls High High High

Containment and Isolation High High High

Personal Protection High Moderate Variable

Administrative Controls Low Low Variable

Behavior Controls Low Low Low

Engineering controls are the preferred way to reduce occupational hazards because they minimize the chances of exposure due to accident or to individual oversight. Engineering

controls can be very expensive, especially when they are retrofitted to older equipment. Engineering controls are usually more effective and economical when built into the original design of the plant. Improper maintenance and operator neglect may result in a breakdown in the effectiveness of such controls, however. An example of engineering controls is the design of heavy equipment to minimize noise and vibration and mounting of machinery on sound-absorbing pads.

Complete automation is one way to achieve isolation of hazards. Another is to contain the hazard by means of an appropriate barrier such as a soundproof blanket over a noisy machine or a vent pipe to carry off a poisonous gas. Hazard containment has the advantage of allowing employees freedom to move about the workplace without encumbrance.

Containment may involve construction of a shell around a machine or placing a barrier between the source and the work area. Isolation may be the removal of a particularly hazardous process to a location away from workers. Both are highly effective ways of dealing with many hazards. Chemical processes are usually tightly contained in an enclosed tank or reaction chamber. Sound-absorbing baffles or enclosures are commonly used to reduce noise exposure. As with engineering controls, however, the effectiveness of containment and isolation often depends on careful maintenance and is susceptible to carelessness. Care must also be taken that an isolated facility does not become an environmental hazard to the surrounding community, as in the case of secondary smelting operations where heavy metals are released.

If hazard containment is not possible (for example if the noisy machine overheats if blanketed or the poisonous gas cannot be vented), the only alternative is worker containment. This can be done either by literally containing the workers themselves, for example in a sound-proof control room, or by issuing personal protective clothing or equipment.

Personal protection is considered generally less satisfactory than engineering controls because the effectiveness of control devices depends on factors that are less easily controlled, including the fit between a personal protective device (such as earplugs or a respirator) and the worker using it, the education and compliance of the worker, and the commitment of the employer in ensuring their proper use. The selection of the proper protective apparatus for the job and the provision of alternative devices from which workers may choose will enhance the success of personal protection. Some hazards can be dealt with only by personal protection, but the effectiveness of personal protection generally is affected by so many technical and behavioral variables that they are not the best approach if engineering controls are possible and feasible.

Administrative controls are used primarily where cumulative exposure is to be kept to a permissable level, as with noise and, controversially, ionizing radiation. Workers are rotated among stations on a regular schedule to reduce the possibility of any one individual receiving an excessive exposure. Administrative controls are useful as added safety precautions but they are not a legitimate substitute for controlling the exposure itself. In acute emergency situations, usually involving radiation, they may be necessary as an extreme temporary measure until the problem is brought under control.

Behavioral controls involve the education and motivation of workers to minimize exposure and to practice safe work habits. They may also involve redesigning the job to avoid dangerous or awkward motions or the placement of warning signs or signals. This is usually considered the least satisfactory approach because it depends on the individual worker's alertness, motivation and comprehension and may be compromised easily by minor distractions, boredom, fatigue, passive-aggressive behavior, ill health, poor eyesight or hearing, misunderstanding, language barriers, and lack of personal motivation.

The optimal solution to a particular problem balances the technical requirements with the available resources and may involve a blend of approaches.

Hazards which can be sampled can be measured and compared to safe levels. If the results show the hazard level to be unsafe, appropriate action must be taken. Hazard monitoring is akin to having an early warning system because it may be possible to detect and deal with the threat before the health of workers is affected.

Worksite monitoring is a technically complex pursuit, usually requiring the special knowledge and skills of an industrial hygienist. Laboratory analysis also calls for capabilities not normally possessed by medical or engineering laboratories. For the majority of smaller companies it is not economically feasible to have an in-house analytical laboratory or an industrial hygienist. In such situations these resources must be contracted from independent occupational hygiene consultation firms now available in many larger centers.

Permissible safe levels of significantly hazardous materials are regulated by national or provincial governments. It is imperative that the occupational health service maintain awareness of these regulated levels, the monitoring which is required and the necessity for reporting results.

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