Occupational poisoning by irritant substances

Basic characteristics of the labor process

Any professional activity is evaluated in terms of its impact on the worker's body. There are two main factors of the labor process:

• Physical work load. This parameter reflects the degree of physical exertion. The main "blow" in heavy labor is taken by the musculoskeletal system (MS). Functional systems that ensure muscular activity are also involved, primarily the cardiovascular and respiratory systems.
• Labor intensity. This characteristic describes the level of intellectual, sensory, or emotional load. During strenuous labor, the central nervous system (CNS) is subjected to predominant impact.

Classification of types of physical labor

Physical labor is defined as a type of work in which the dominant load falls on the structures of the musculoskeletal system. In occupational hygiene, it is customary to divide physical labor into categories depending on the volume of muscle mass involved in performing production operations:

1. Local work. No more than 1/3 of the total body muscle mass is involved in the labor process. This type is characterized by the lowest overall levels of energy expenditure.
2. Regional work. Work operations require the participation of 1/3 to 2/3 of the worker's entire musculature.
3. Global work. More than 2/3 of the muscle mass is involved in the process. This type of labor is associated with maximum levels of energy expenditure.

Based on the difference in the body's energy expenditure, experts distinguish four degrees of physical work intensity: light, moderate, heavy, and very heavy.

Hygienic standardization of energy expenditure

To preserve workers' health and prevent excessive fatigue, the maximum value of average shift energy expenditure is strictly regulated. These standards are calculated for a standard working shift lasting 7–8 hours:

• When performing global physical work, energy expenditure must not exceed 4.2 kcal/min.
• For regional work, a limit of 2.8 kcal/min is established.
• For local muscular work, the indicator is limited to 1.7 kcal/min.

Specifics and prevention of local work

Despite minimal total energy expenditure, it is precisely during local physical work that pathological muscle overstrain most frequently develops. This paradox is easily explained: the entire biomechanical load is concentrated on an extremely limited number of muscles and muscle fibers, leading to their rapid local exhaustion.

To reduce the negative impact of heavy (global and regional) and local labor, comprehensive measures are implemented:

• Technical and technological: mechanization, automation of processes, and process modifications to directly reduce physical load.
• Physiological standardization: strict control of work and rest time.

Special recommendations for local work: The most important task is to reduce the number of stereotyped movements and minimize static loads (since static work fatigues muscles significantly faster than dynamic work). This is achieved through the introduction of minor mechanization tools (various clamps, pushers, automatic product turners). In addition, it is necessary to reduce the required physical effort when performing routine operations—for example, by replacing manual mechanical tool drives with electric ones.

Class and exam questions

What else to study on this topic

• Methods for calculating energy expenditure in the workplace (chronometry and calorimetry).
• Specific occupational diseases of the musculoskeletal system in local labor.
• Ergonomic principles in the design of minor mechanization tools.
• Criteria for assessing labor intensity (sensory, emotional, and intellectual loads).

Other topics in "Chapter 6. Fundamentals of Occupational Hygiene and Physiology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.