Occupational Medicine
A Basic Guide

08: Industry Specific Pearls

Dan Mirski, MD, MPH

The manufacturing sector focuses on transforming raw materials into goods that meet human needs. The industry as a whole is responsible for almost one-third of all occupational illness cases according to the U.S. Bureau of Labor Statistics. Most of the occupational diseases described in the mining section of this chapter are also therefore quite prevalent in the manufacturing industry. Workers are subjected to traumatic and repetitive musculoskeletal injuries, dermatitis, corneal injuries, especially with welding or chemicals, and occupational asthma as well as myriad other injuries and diseases. There are, however, a few ailments that are specific to the manufacturing sector; the most common of which is noise-induced hearing loss (NIHL).


Hearing Loss


Occupational NIHL is the single most common work-related illness. The Occupational Safety and Health Administration, overseen by the U.S. Department of Labor, and the National Institute for Occupational Safety and Health (NIOSH), overseen by the Centers for Disease Control and Prevention, both mandate and collect, respectively, audiometric yearly evaluations from workers who are subjected to excessively high occupational noise exposure. Such noise exposure is defined as exceeding 85 decibels (dB) over an eight-hour workday. Employers in these situations are required by OSHA to enroll their workers in a hearing-conservation program. Extended noise exposures that reach 85 dB can cause permanent damage to auricular hair cells, resulting in hearing loss. By comparison, a normal household blender usually operates at around 88 dB.


A hearing conservation program mandates that an employee must wear hearing protection and participate in regular audiometric evaluations. Occupational NIHL produces a specific audiometric elevation in hearing threshold at 4,000 Hz. This is known as the “4K hearing notch,” which is typical of occupational NIHL. Occupational hearing loss is such an important issue because it is very common and produces a devastating disability that is 100% preventable.


The prevalence of NIHL is actually greatest in the mining industry; however, manufacturing has the greatest number of workers exposed to continuous 85 dB on an eight-hour average and thus produces the greatest number of occupational NIHL patients.


Musculoskeletal Injuries


The manufacturing process involves significant repetitive upper extremity work. This results in an increased likelihood for cumulative overuse tendinopathiesv (see also Chapter 2, Musculoskeletal Injuries). It is important for primary care providers to recognize that a patient presenting with an upper extremity disorder may need not only treatment, but also working an injury classification.


Rotator cuff injuries are common and best treated with work restrictions that limit above-shoulder work and lifting. If a permanent disability results at the shoulder level, the permanent impairment rating is based on the range of motion (ROM) that is lost, as measured in forward flexion, extension, abduction, adduction, and external and internal rotation. If any of these ROM are impaired, providers can access the AMA Guides to the Evaluation of Permanent Impairment textbook, which has tables listing the impairment for each ROM abnormality—as well as for other arm tendinopathies as well.


Diagnosis of elbow impairment is based on any lack of flexion, extension, supination, or pronation, as measured with a goniometer. The most common cumulative trauma disorder of the elbow is a lateral epicondylitis injury. It is best treated with rest and a “tennis elbow” splint. NSAIDs (oral and topical) and physical therapy are often used, but as with many such injuries, it is not certain that these help any more than simply “buying time” for the injury to heal on its own. Unfortunately, these overuse injuries tend to recur once the work restrictions are lifted unless engineering controls are implemented. In the manufacturing sector, such controls involve using better designed tools (such as with wider handles), fewer repetitive arm movements, and improved ergonomic controls.


Wrist tendinopathies include DeQuervain’s (DQ) tenosynovitis and carpal tunnel syndrome (CTS). DQ is an inflammation of the two tendons—abductor pollicis longus and extensor pollicis brevis—at the base of the thumb. On exam, the practitioner can elicit a positive Finkelstein maneuver, where the thumb is flexed down across palm with fingers flexed over and wrist extended laterally. A nighttime rigid wrist splint can be quite helpful, as it can be with carpal tunnel.


In CTS, the median nerve compression can be reproduced with Tinel’s sign and Phalen’s test. Interestingly, the occupational causation of CTS is not as well established as its association with obesity, diabetes, pregnancy, and hypothyroidism. Nonetheless, according to the Guides, CT surgery results in a 3% whole body impairment rating under worker’s compensation. Nerve conduction studies and electromyography are the mainstay of diagnosis after physical examination. A Jamar dynamometer is used to evaluate grip strength in occupational disorders that produce hand weakness.


Chemical Exposure


Theoretically, all hazardous chemicals used in the manufacturing process should come with a Material Safety Data Sheet (MSDS or SDS) produced by the manufacturer. This document contains important information on potential health hazards associated with working the chemical. It also contains information on its reactivity, fire potential, and environmental impact, as well as how to work safely with it. When an injury occurs from a chemical used in the manufacturing process, the treating health care provider can request a copy of the MSDS. As with all injuries, a company representative, should bring the worker to the health care provider, and bring along the MSDS. OSHA requires that every workplace maintain MSDSs for all hazardous chemicals used and make them readily available to all workers.


Many providers outside of the occupational health specialty are unaware that most chemicals used in manufacturing are absolutely unregulated. Most chemicals have never been formally tested for toxicity or carcinogenicity, and therefore it is not known if they are hazardous. NIOSH issues recommended exposure limits (RELs), and OSHA regulates permissible exposure limits (PELs) on what appears to be an enormous number of chemicals but is actually only a tiny proportion of those used in industry. The case of nanotechnology manufacturing illustrations this important point.


The last decade has seen a tremendous growth in nanotechnology, in both the medical and manufacturing industries. Use of these light, strong, microscopic particles (one-billionth of a meter) shows great promise and benefit to society. However, their introduction has been so quick and widespread that we do not yet know the medical implications for workers handling them. NIOSH and OSHA are working to evaluate the health implications, but to date there are no regulations or occupational exposure limits (OELs) specific to nanoparticles. Inhaling nanoparticles could potentially cause pulmonary disorders similar to those related to the inhalation of pneumoconiosis-associated dust particles or at the very least result in sensitization and occupational asthma. Excretion of nanoparticles could in theory also cause glomerular and interstitial diseases, as well as the development of occupational skin disorders from prolonged contact.


Advances in technology can often outpace the medical understanding needed to support them safely. In the aerospace industry during the 1940s for example, we knew how to accelerate a body inside an aircraft to multiple Gs without fully understanding what the physiological and medical implications of such forces would be to an individual. Some portions of the manufacturing sector are on a similar path of high-tech growth and innovation—with possible medical implications.