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Dust detection is a key aspect of occupational health monitoring, and the focus of this detection lies in sampling; therefore, dust sampling is the most critical element within occupational health monitoring. However, given the relatively complex sampling environment at work sites and the numerous interfering factors, the sampling method becomes particularly important. Choosing the right sampling method is the primary step in reducing detection errors. Dust sampling is divided into two categories: total dust sampling and exhaled dust sampling. Each of these categories is further split into individual sampling and fixed-point sampling. Here we will provide an evaluation of these four methods: Total dust sampling: 1. Individual total dust: For individual total dust sampling, sampling boxes with a diameter of 37 mm or 40 mm are used, with a sampling flow rate of 1–5 L/min. An individual sampler is employed, and the air intake direction mimics natural human breathing – that is, from bottom to top ； The sampling time corresponds to the total exposure time of the workers ； 2. Fixed-point sampling: For fixed-point sampling, sampling cartridges with a diameter of 37 mm or 40 mm are used, with a sampling flow rate of 15–40 L/min; fixed-point dust samplers are employed, and no specification is given regarding the direction of air intake ； The sampling time is 15 minutes, and sampling is carried out during the period when the concentration is at its highest, at the work stations where the concentration is highest ； By comparing the two methods, it can be seen that for individual dust measurements, sampling should be carried out in the direction of breathing; the air inlet should be directed downward, and the dust collected should mainly consist of particles smaller than PM10. Currently, in China, the standard sampling method for fixed locations involves an air inlet oriented horizontally, resulting in dust samples that are primarily composed of larger particles. However, according to the GBZ2.1 standards, total dust refers to the dust that can enter the entire respiratory tract ； Large particles of dust cannot enter the respiratory tract; the dust that does reach the respiratory tract is mainly those with a size of less than PM10. If we do not take into account differences in time when comparing the two methods of dust intake, we conduct several comparison tests: Comparison methods: horizontal sampling at a rate of 9 L/min at a fixed location and vertical sampling at a rate of 5 L/min at a fixed location ； Comparison location: 1. Underground tunneling face in coal mines ； 2. Return airway in coal mine shafts ； 3. Tail end of conveyor belt in coal mine shafts ； Sampling location, Sample number, M1 (mg), M2 (mg), Δm (mg), V (L), C (mg/m3): At the transfer point of the excavation face in the extended section of the return air drift at 210606, Horizontal 01: 11.03, 15.39, 4.36, 135.64, 32.14; Vertical 01: 13.27, 14.19, 0.92, 77.090, 11.93. In the return air duct of the excavation face of the return air drift at 210606, Horizontal 02: 13.90, 15.56, 1.66, 135.58, 12.24; Vertical 02: 12.77, 13.53, 0.76, 75.639, 10.05. On the return air side of the belt conveyor at the main inclined shaft, Horizontal 03: 13.09, 15.19, 2.10, 135.60, 15.49; Vertical 03: 11.22, 11.68, 0.46, 75.834, 6.07. Based on these data, it can be seen that the concentrations obtained using the horizontal air intake sampling method are about 3 times higher than those obtained using the vertical air intake sampling method at locations where dust is generated (Locations 1 and 3). At Location 2, where no dust is generated, the concentration is approximately 1.2 times higher. An analysis of the dispersion of the dust shows that at Locations 1 and 3, the dust collected using the horizontal air intake method consists mainly of large particles, while almost no large particles are present in the dust collected using the vertical air intake method. At Location 2, the dispersion of the two types of dust collected is similar, with both being small particles. It can be seen that the correct method for fixed-point dust sampling is vertical air intake sampling; then why do the fixed-point samplers available on the market all use horizontal air intake? Since they are samplers used for environmental hygiene, they are not suitable for occupational health purposes. During environmental hygiene sampling, large particle matter is virtually absent (unless there is a sandstorm), so the direction of air intake does not affect the sampling results. For occupational health sampling, only the vertical air intake mode can be used, not the horizontal air intake mode, as shown in the figure. Dust exhalation sampling: 1. Individual dust exhalations: Two separation methods are used for individual dust exhalations – cyclone separators and impact separators. The specific sampling flow rate varies depending on the capacity of the separator; however, the separation curve must conform to the BMRC or ACGIH curves (as shown in the figure). The sampling time is generally equal to the total time during which the worker is exposed to dust throughout the day ； 3. Fixed-point dust sampling: The fixed-point dust sampling method also employs either a cyclone separator or an impact separator; the separation curve is required to conform to the BMRC or ACGIH curves. The sampling duration is 15 minutes, and sampling should be carried out during the periods when the concentration is at its highest, i.e., at the work stations where the concentrations are highest ； We used these two separations to conduct another set of comparison tests ； Comparison method: Fixed-point transverse sampling at 20 L/min and fixed-point longitudinal sampling at 10 L/min ； Comparison location: 1. Underground tunneling face in coal mines ； 2. Return airway in coal mine shafts ； 3. Tail end of conveyor belt in coal mine shafts ； Sampling location, Sample number, M1 (mg), M2 (mg), Δm (mg), V (L), C (mg/m3): At the transfer point of the excavation face in the extended section of the return air drift at 210606 – Impulse type 01: 12.52, 17.01, 4.48, 300, 11.59; Cyclone type 01: 13.32, 13.64, 0.32, 150, 2.12. In the return air alley of the excavation face of the return air drift at 210606 – Impulse type 02: 12.35, 12.76, 0.41, 300, 1.37; Cyclone type 02: 11.99, 12.18, 0.19, 150, 1.25. On the return air side of the conveyor belt in the main inclined shaft – Impulse type 03: 12.68, 13.94, 1.26, 300, 4.21; Cyclone type 03: 12.91, 13.08, 0.17, 150, 1.15. As can be seen from these data, there is a significant difference in concentration levels when using the impulse and cyclone sampling methods at the locations where dust is generated (locations 1 and 3); whereas at the location where no dust is generated (location 2), the concentration levels are quite similar. An analysis of the dispersion of the samples also shows that at locations 1 and 3, the impulse sampling method results in a higher amount of large particle dust compared to the cyclone sampling method, while at location 2, the amounts of dust from both methods are similar ； Why does this phenomenon occur? To answer this question, we must start with the separation curve certification test and the principles of these two methods. 1. Certification test method: When certifying the separation curve of any type of separation device, aerosols are generated using aerosol generators with different particle sizes. After separation by the respective separators, the separation efficiency is compared. An aerosol size of 4 μm results in a separation efficiency of 50%, which meets the ACGIH curve, while an aerosol size of 5 μm also yields a separation efficiency of 50%, meeting the BMRC curve ； In this experiment, separation tests were conducted on aerosols of different particle sizes separately; all the aerosols were not mixed together for testing at the same time. 2. Cyclone separator: When air enters through the inlet of the cyclone separator, the airflow rotates in a direction tangent to the inner wall of the separator; larger dust particles settle more rapidly and end up in the chamber designated for large particles, while smaller dust particles settle more slowly and get trapped on the filter membrane. 3. Impact separator: After air enters through the inlet of the impact separator, it strikes the impact plate directly; the impact plate is coated with silicone oil, which causes dust particles of different sizes to adhere to it in proportion, while the remaining dust is captured by the filter membrane. From the principles of these two methods, it can be seen that cyclone separators are able to separate dust that meets the requirements of curves A and B even when there are many large particles, as they use sedimentation for separation. However, impact separators encounter problems: 1) During certification tests, no testing was conducted on large particles, and with the lateral air intake mode in use, particles of any size may enter the separator ； 2. The impact plate is simultaneously coated with large-particle dust of different sizes, making it difficult for smaller particle dust to adhere to it ； 3. The concentration of large-particle dust is high; it quickly becomes saturated, and then a large amount of such dust enters the filter membrane. Same question: Why are impact separators of this kind used for collecting respirable dust in the market? The answer is the same: they are devices used for environmental sampling. During environmental sampling, the conditions and location are such that there are no factors that could generate large particles of dust, and thus no interference with impact separators. The situation is different in the field of occupational health, where respiratory dust sampling is carried out at times when large particles of dust are generated and interference from them is at its worst. Therefore, impact-type respiratory dust samplers with lateral air intake cannot be used; instead, cyclone-type respiratory dust samplers or impact-type samplers with the air inlet facing downward should be employed.