Knowledge of occupational hazard control

Thread Content

1. What is the significance of measuring occupational hazards? The higher the concentrations of dust and toxins in the working environment, as well as the greater the levels of noise and high-frequency sounds, the greater the damage to workers’ health. Only through regular and representative measurements can it be determined whether the concentration or intensity of the occupational hazards to which one is exposed meets **health standards**, thereby allowing for an objective assessment of the hygiene conditions in the working environment. Through measurement, it provides a basis for improving protective facilities as well as data for evaluating their effectiveness. 2. What serves as the basis for establishing exposure limits for toxic substances in workshop air? The physical and chemical properties of the chemicals, data from animal experiments and human toxicology studies, as well as information from on-site occupational health surveys and epidemiological studies, all serve as such a basis. 3. What are the exposure limits for harmful substances in workshop air? The exposure limits for harmful substances in workshop air are specified values for the concentration of such substances in the air of workshops, set forth to protect the health of workers. There are various ways in which these limits can be expressed. (1) Maximum Allowable Concentration (MAC). It refers to a concentration that must not be exceeded in any representative sample, and is applied in countries such as China and the Soviet Union. (2) Threshold value (TLv). It refers to the exposure limits recommended by the **American Conference of Industrial Hygienists**, and is further divided into the following types: ① Time-Weighted Average Threshold Limit Value (TLV-TWA). The time-weighted average concentration over a normal 8-hour workday or 40-hour workweek is such that repeated exposure at this level will not cause adverse effects in almost all workers. ②Short-term exposure limit (TLV-STEHL). At this concentration, workers can be exposed continuously for a short period of time without it causing: A. irritation; B. chronic, reversible tissue changes; C. a level high enough to increase the risk of accidental injuries, reduce the ability to rescue oneself, or significantly lower work efficiency. STEL refers to the time-weighted average exposure limit, whereby the exposure time per contact shall not exceed 15 minutes; exposure may occur no more than 4 times a day, with at least 60 minutes between two consecutive exposures. ③Upper limit value (TLV—C). The maximum concentration that must not be exceeded, even for an instant. (3) Permissible Exposure Level (PEL). These are the exposure limits set out in the occupational safety and health standards issued by the Occupational Safety and Health Administration (OSHA) of the U.S. Department of Labor; upper limits or 8-hour time-weighted average limits are specified depending on the properties of the hazardous substances. (4) Health-based occupational exposure limit (HBOEI). This is a type of exposure limit proposed in recent years by a specialized research group at the World Health Organization (WHO). When the concentration of harmful substances in the studio air is at such a \"limit\" level, the adverse effects on workers’ health over the course of their lives do not reach a \"significant risk level.\" When establishing such exposure limits, factors such as engineering and technical measures or economic conditions are not taken into account. The different values **can be adjusted according to each country’s national conditions, to serve as the applicable limits for that country. (5) Maximum allowable biological concentration (MA: BC). Also known as the biological exposure limit. The concentrations of industrial toxins or their metabolites in blood, urine, exhaled breath, hair, or other biological materials are collectively referred to as toxin concentrations in biological tissues. By studying the quantitative relationship between this concentration and the level of exposure to the toxin, and in accordance with the principles behind establishing MAC values, the highest tolerable limit of the toxin (or its metabolites) in biological tissues is defined as the maximum allowable biological concentration. 4. What is industrial ventilation? What are its main types? Industrial ventilation is one of the important sanitary technical measures for controlling dust, harmful gases or vapors in workshops and improving the microclimate within them. Its main function is to remove the polluted, humid, overheated, or undercooled air from the working area in the workshop, and to introduce clean air from the outside into the workshop in order to improve its air quality. The main types of industrial ventilation are: (1) Based on their power source, industrial ventilation can be divided into natural ventilation and mechanical ventilation. Natural ventilation relies on the thermal pressure generated by the temperature difference between indoor and outdoor air, as well as the wind pressure caused by outdoor winds, to drive air flow; mechanical ventilation, on the other hand, uses the pressure difference between the inside and outside of a ventilation system created by fans to direct air flow in a specific direction. (2) In terms of the scope of ventilation, industrial ventilation can be divided into local ventilation and general ventilation. Local ventilation operates in the specific area where workers are working, with the aim of protecting their health rather than improving the overall environment of the workshop. General ventilation affects the entire workshop and is suitable for areas where workers’ work positions are not fixed. (3) In terms of ventilation methods, industrial ventilation can be further divided into exhaust ventilation and supply ventilation. Exhaust ventilation refers to the use of ventilation methods to remove harmful substances or humid, hot air from the workshop, keeping them away from the workers. Supply ventilation, on the other hand, involves introducing clean air from outside the workshop into it, so as to directly affect the workers or improve the overall air quality in the workshop. To control dust, harmful gases, or vapors in the workshop, local exhaust ventilation is primarily used. To improve the microclimate in the workshop, local or overall air supply can be used, as well as exhaust ventilation; the specific choice depends on factors such as the size and distribution of heat sources, production characteristics, and outdoor weather conditions. 5. How to choose local exhaust ventilation, supply ventilation, and general supply ventilation? (1) If preventing the dispersion of dust or harmful gases within the workshop is the goal, local exhaust ventilation is primarily used. (2) If the workshop is large but has few operators, it is impractical to use general ventilation for cooling or to supply hot air; in such cases, local ventilation is often used to improve the microclimate in the area where the workers are working. The simplest form of local air supply is an electric fan. (3) Ventilating the entire workshop is known as general ventilation. General ventilation is typically used to improve the microclimate in workshops and as a supplementary measure to local ventilation for preventing harmful gases. The simplest form involves installing a ventilation tower in the workshop, with air intake windows on the walls, to utilize natural ventilation for air exchange. When designing mechanical ventilation, the following approaches are generally adopted: ① mechanical air supply with natural exhaust through doors and windows; or ② mechanical exhaust with natural air intake through doors and windows. For workshops where high air cleanliness is required due to processing needs, an air-conditioning and recirculating filtered ventilation system can be used, with an appropriate amount of fresh air being supplied.