Dehydroabietic acid as a biomarker for exposure to colophony

BACKGROUND: Colophony (rosin) is a natural product derived from the resin of coniferous trees with many industrial applications including soldering fluxes. Exposure to colophony fume through soldering is one of the leading causes of occupational asthma in the UK. AIMS: To assess occupational exposure to colophony from solder fume at selected workplaces in the UK and to investigate the use of dehydroabietic acid (DHA) as a biomarker of exposure. METHODS: Six companies in the UK electronics industry were visited and occupational hygiene assessments of extent and control of exposure to rosin-based solder flux fume were undertaken. Urine samples were analysed for one of the main constituents of rosin, DHA. RESULTS: There was a positive linear relationship between airborne exposure to solder fume and urinary DHA level. The levels of urinary DHA measured in UK workers were significantly lower than those previously measured in African workers because of the use of appropriate exposure control measures, for example, local exhaust ventilation with fixed ducting and flexible hose, tip extraction, etc. It is suggested that good occupational hygiene practice would result in urinary DHA levels of <3 micromol/mol creatinine in a post-shift urine sample. CONCLUSIONS: Urinary DHA is a valid biomarker of exposure to colophony in solder fume. Further work on the excretion kinetics of urinary DHA, the possibility of skin absorption and further occupational hygiene surveys would be beneficial.     

Workplace Exposure to Rosin-based Solder Flux Fume During Hand Soldering

The patterns and extent of exposure to rosin based solder flux fume have been investigated in two surveys and a number of individual site visits carried out by the UK Health and Safety Executive (HSE). Determination of solder fume was by measurement of airborne resin acid particulate. Both static and personal sampling was carried out over time periods ranging from 15 minutes to several hours. Resin acid concentrations were found to vary from less than 1 μgm^-3 to 2289 μgm^-3 . The effects of various types of local exhaust ventilation on resin acid concentrations have been observed. On-tool tip extraction systems were generally found to be the best control measure available; however good design, positioning and system maintenance is essential for efficient capture of the fume. The resin acid concentrations detected at these twenty-six sites suggest that the proposed British long and short term occupational exposure limits are realistically attainable targets, particularly where good working practices and:or effective fume control measures are in place. ©1998 British Occupational Hygiene Society. Published by Elsevier Science Ltd.     

Local exhaust ventilation for the control of welding fumes in the construction industry--a literature review

Arc welding is a common unit operation in the construction industry, where frequent changes in location and welding position make it more difficult to control fume exposures than in industries where fixed locations are the norm. Welders may be exposed to a variety of toxic airborne contaminants including manganese (Mn) and hexavalent chromium (CrVI). Local exhaust ventilation (LEV) is a well-known engineering control for welding fumes but has not been adopted widely in the construction industry. This literature review presents data on the performance of a variety of LEV systems for welding fume control from the construction (five references), shipyard (five references), and other industries. The studies indicate that LEV can reduce fume exposures to total particulate, Mn, and CrVI to levels below currently relevant standards. Field studies suggest that 40-50% or more reduction in exposure is possible with portable or fixed LEV systems relative to natural ventilation but that correct positioning of the hood and adequate exhaust flow rates are essential. Successful implementation of extraction guns for gas metal arc welding (GMAW) and flux core arc welding has been demonstrated, indicating that a successful balance between extraction airflow and shielding gas requirements is possible. Work practices are an important part of achieving successful control of fume exposures; in particular, positioning the hood close to the arc, checking exhaust flow rates, and avoiding the plume. Further research is needed on hood size effects for controlling welding fume with portable LEV systems and identifying and overcoming barriers to LEV use in construction.     

Numerical investigation of turbulent diffusion in push-pull and exhaust fume cupboards

The aim of this study is to investigate airflow motions and associated pollutant distributions in fume hoods. Currently, most exhaust fume hoods are designed to use an airflow induced by a fan at the top to remove pollutants. Ambient fluids are drawn, flowing toward the opening and subsequently turning to the outlet at the roof. Pollutants are supposedly captured by the airflow and brought out from the cupboard. The present numerical study based on the finite-volume method and the standard k-epsilon turbulence model simulates flow patterns and pollutant distributions in an exhaust fume hood with and without a manikin present. Subsequently, a push-pull air curtain technique is applied to a fume cupboard. To investigate the capturing performance of a push-pull fume cupboard, numerical approaches are used to simulate flow and concentration variations. Numerical results reveal that four characteristic flow modes exist for a variety of speed ratios of push-pull flows and openings. A concave curtain mode which has a fast pull flow and a weak push flow is suggested for the operation of a push-pull fume cupboard. According to ANSI-ASHRAE Standard 110-1995, the local concentration at the specified point is <0.1 parts per million (p.p.m.). Meanwhile, we also examine concentration variations at 12 selected points in front of the sash, and all where the concentration is <0.1 p.p.m. A manikin is put in front of the sash to observe its effect. As a result, the flow and the concentration contours in a push-pull fume cupboard are not affected by a manikin. In terms of those predicted results, it turns out that a push-pull fume cupboard successfully captures pollutants and prevents an operator from breathing pollutants.     

Numerical investigation and recommendations for push-pull ventilation systems

This study presents numerical simulations of push-pull ventilation systems. A push-pull system is a device commonly used in capturing pollutants from large tanks used in industrial chemical processes. An air jet is blown from one side of a tank and collected by an exhaust hood on the opposite side of the tank. In this study, a finite volume model coupled with the standard k -epsilon turbulent model is employed to describe the flow structures and characteristics. Moreover, the turbulence mass transfer equation is adopted to show the concentration distribution above the open surface tank. All the flow fields can be classified according to four dominant modes, i.e., dispersion, transition, encapsulation, and strong suction. The push and pull flow velocities should be adjusted into encapsulation and strong suction modes to ensure all pollutants can be captured by the exhaust hood. Other geometric parameters such as the flange size, pull-channel size, offset distance, etc., also influence the flow characteristics. For a variety of lengths of tanks and pollutant evaporation velocities, the push and pull flow velocity must be matched to achieve optimal operation. Furthermore, the flange size and other parameters are determined to enhance the capture efficiency of the push-pull system. Recommendations for design guidelines are introduced in this study.     

Local ventilation solution for large, warm emission sources

In a foundry casting line, contaminants are released from a large area. Casting fumes include both volatile and particulate compounds. The volatile fraction contains hydrocarbons, whereas the particulate fraction mostly comprises a mixture of vaporized metal fumes. Casting fumes lower the air quality in foundries. The design of local ventilation for the casting area is a challenging task, because of the large casting area and convection plumes from warm moulds. A local ventilation solution for the mould casting area was designed and dimensioned with the aid of computational fluid dynamic (CFD) calculations. According to the calculations, the most efficient solution was a push-pull ventilation system. The prototype of the push-pull system was built and tested in actual operation at the foundry. The push flow was generated by a free plane jet that blew across the 10 m wide casting area towards an exhaust hood on the opposite side of the casting lines. The capture efficiency of the prototype was determined by the tracer gas method. The measured capture efficiencies with push jet varied between 40 and 80%, depending on the distance between the source and the exhaust. With the aid of the push flow, the average capture efficiency was increased from 40 (without jet) to 60%.     

Improved local exhaust control by directed push-pull ventilation system

Experiments using the directed push-pull ventilation technique were conducted on a general type of local exhaust ventilation installation. The exhaust (pull) system consisted of a square hood, while the push system consisted of one or two slot jets or two round jets. The two slot or round jets were located behind and beside a mannequin (the mannequin simulated the worker's position). The one slot jet was located between the smoke source and the mannequin. Under experimental conditions, the push-pull system reduced the amount of smoke in the mannequin's breathing zone even when the exhaust system volume flow rate necessary for capture of the smoke decreased approximately 50%. Generally, no difference between the slot and round jet control performance was found. The experiments showed that the directed push-pull ventilation system can be used effectively to reduce the contaminant emission into a workroom, if the jets are located so that the eddy currents induced by the worker or other obstructions are minimized or eliminated.     

Evaluation of the reverse flow around a worker's body produced by a local exhaust hood]

Recent studies have shown that a reverse flow often occurs in a unidirectional airflow in push-pull ventilation and may transport contaminants from the source into a worker's breathing zone. The same problem may arise in local exhaust ventilation when the contaminant source is located in the worker's wake region. In this study, organic solvent work with local exhaust ventilation was duplicated in a laboratory and the details of the reverse flow around the worker's body produced by the ventilation were experimentally investigated. In order to evaluate the influence of the reverse flow on the exposure of the worker, experiments with a mock-up mannequin (dummy worker) and a local ventilation system which was equipped with an exterior type hood and an enclosure type hood were conducted. The exposure level and the contaminant leakage from the hoods in several conditions were measured by means of a smoke test and tracer gas method. Ethanol vapor was used as a tracer gas. With the exterior type hood, the reverse flow visualized by the smoke was observed in front of the standing dummy worker but could not be observed when the dummy worker was seated. From the tracer gas measurements, it was proved that the exposure due to the reverse flow was not so serious at a capture velocity of > 0.4 m/s, but < 10 ppm contaminant leakage from the exterior hood had been recognized independently of the capture velocity. With the enclosure type hood, exposure due to the reverse flow could be controlled with a capture velocity of > 0.8 m/s. Although the contaminant leakage from the hood due to the reverse flow was not obvious with the enclosure type in any condition, caution should be exercised to prevent exposure when the worker is seated. Regardless of the hood type, the increase in the capture velocity was effective in decreasing exposure due to the reverse flow.     

Development of push-pull ventilation

Push-pull ventilation (air is blown across a contaminant generation area toward an exhaust hood) can have distinct advantages over exhaust ventilation alone. It can control contaminant emission into the workplace better than exhaust only, and much less conditioned air must be exhausted so there are energy savings. This paper presents suggested push and pull flow rates for open surface tank operations such as plating. About 98% of the contaminant generated can be captured by a push-pull system using the proper flow rates.     

Health hazards of soft soldering in the electronics industry

Soft Soldering has been used as a method of joining two metals for centuries. It is a commonly undertaken process in the electronics industry but only relatively recently have health hazards related to the activity been reported. Irritative symptoms are common but fumes from rosin cored solder are now additionally recognized as a cause of occupational asthma. Soldering of polyurethane enamels can also produce occupational asthma, the causative agent being toluene-di-isocyanate. Skin problems can also arise from contact with rosin flux. Control measures are necessary to control the exposure of individuals to solder fumes both in relation to the lead content of the solder and the problems related to the flux. Such control is achievable and can dramatically reduce the personal exposure to solder fumes.     

Determination and interpretation of total and transversal linear efficiencies in push-pull ventilation systems for open surface tanks

A real-scale pilot installation simulating an open surface treatment tank with a push-pull ventilation system has been designed. From experiments carried out, typical representations of the total and transversal linear efficiencies show that when total efficiency is related to push flow rate, taking as a parameter the pull flow rate, a parabolic profile is obtained with a maximum point or plateau that increases as the pull flow increases. When the transversal linear efficiency is analysed, three general zones where losses occur to the exterior can be detected: (i) when the push flow rate is low, any distortion in the wall jet, whether external (e.g. in the air flow inside the workshop) or internal (e.g. thermal effects), provokes an escape from contaminant; (ii) in the impact zone, where the push flow impacts on the tank surface, distortion increases as the push flow rate increases; (iii) when the push/pull flow rate ratio increases and preferential currents are produced inside the exhaust hood, these escape and cause substantial losses in efficiency.     

Numerical simulations to determine the most appropriate welding and ventilation conditions in small enclosed workspace

In order to improve arc welding work in a small enclosed workspace, numerical simulations were conducted to find the most appropriate welding and ventilation conditions, such as welding currents, hood position and flow rates with no blowhole formation. In the simulations, distributions of airflow vectors and fume concentrations were calculated for two hood opening positions: one faced a welder's breathing zone, the other a contaminant source. As a result it was predicted that a hood opening facing a breathing zone remarkably lowered the fume concentration in the breathing zone compared with that facing a contaminant source. The reliability was confirmed in CO2 arc welding experiments in the enclosed workspace by using a welding robot. In addition, the number of blowholes in welds, examined with x-ray, decreased with the increase in the welding current and with the decrease in the exhaust flow rate. These results showed that the fume concentration near welder's breathing zone and the number of blowholes could be reduced effectively by appropriate selection of the welding current and hood position, and it was confirmed that the numerical simulations were sufficiently useful to predict these appropriate welding conditions.     

Visualization of airflows in push-pull ventilation systems applied to surface treatment tanks

A pilot installation was designed that simulates a surface treatment tank fitted with a push-pull ventilation system. The installation contained elements for measuring and controlling the operational variables (flow rate and tank temperature) and smoke generating equipment for injecting smoke through the holes of the push unit and from the tank surface. Visual observation and video recording of the flows involved meant it was possible to follow the qualitative behavior of the push flow rate along the tank surface and to identify any emissions not captured by the exhaust system. It was possible to differentiate the initial semifree push curtain, its impact with the tank surface, the wall jet that moved toward the exhaust, and its entrance into the exhaust. The methodology proposed is complemented by a quantitative technique for measuring the efficiency, using sulfur hexafluoride as tracer, which permits the causes and location of losses in the ventilation system to be determined.     

Recommendations for the design of push-pull ventilation systems for open surface tanks

Open surface tanks used in industrial processes often need ventilating to remove harmful pollutants from the working environment. One method which can be used is the so-called side push-pull ventilation system, in which a jet of air is blown (or pushed) from one side of the tank and collected (or pulled) by an exhaust hood on the opposite parallel side. This system is particularly useful for large tanks where access requirements preclude the use of an overhead canopy, and the size of the tank makes side (or rim) exhaust systems prohibitively expensive.Existing design guidelines for push-pull systems vary greatly, although most agree that the system can yield air savings of up to 50%. Starting from an understanding of the nature of the fluid flow this paper develops guidelines for the important parameters of the system and compares these to the recommendations given in earlier work.     

Methodologies for determining capture efficiencies in surface treatment tanks

Methodologies are proposed for determining capture efficiencies in the ventilation systems of surface treatment tanks, using test-scale equipment. The equipment, which incorporates a lateral and push-pull ventilation system, can measure and control the variables of interest because it incorporates a tracer gas generator (sulfur hexafluoride, the concentration of which is measured by infrared spectrometer). The experimental methodologies described determine total efficiency (when the tracer is emitted uniformly from the whole surface of the tank) and the so-called transversal linear efficiency (when the tracer is emitted linearly through a perforated tube situated over the tank, parallel to the exhaust hood face). The analytical and graphical relationships that can be are established between the two efficiencies make it possible to detect where the emissions not captured by the ventilation system are produced (i.e., losses to the outside). At the same time, such losses can be quantified. Several experiments, results of which are analyzed by the methods described, are included.     

Some engineering countermeasures to reduce exposure to welding fumes and gases avoiding occurrence of blow holes in welded material

Recently, open-type push-pull ventilation systems have been widely employed as effective substitutes for the conventional local exhaust ventilation system, and have prevailed at many welding workshops in Japan. In this study, the effect of the uniform velocity on carbon dioxide (CO2) shielding arc welding was examined by laboratory experiments. The ventilation system examined in the experiments successfully fulfilled the requirement for open-type push-pull ventilators prescribed in Japanese regulations (ordinances). It was proved that the velocity at any points in the capture zone fell in the range of 50 to 150% of the average capture zone velocity. Welding defects could be avoided by controlling the flow rate of shielding gas. Unless the capture velocity exceeded a 0.8 m/s, the formation of blow-holes in the welded metal could be prevented at the shielding gas flow rate of 20 L/min. If the flow rate was provided at 30 L/min and 40 L/min, blow-holes didn't form at the capture velocity of 1.2 m/s and 1.6 m/s, respectively. At a capture velocity of faster than 0.3 m/s, the fume concentration at welder's breathing zone was reduced to a level below the limit values: ACGIH (TLV) and Japan Welding Engineering Society (CLV#). These data are important for designing open-type push-pull ventilation in the welding workshop. The other engineering countermeasures currently employed in the welding work in Japan, such as fume collecting torch and general ventilation, are also concerned in this report. #: Control Limit Value.     

检验科实验室房间压力控制解决方案

随着现代科学技术的高速发展,越来越多的建筑工程,例如制药厂、医院乃至各行各业的实验室,都对洁净的室内环境提出了更高的要求.而对室内压力的良好控制是达到实验室室内环境的必备条件.此外,实验室中与房间压力相关的设备,例如通风柜的控制,对整个房间的压力控制也至关重要.文章讨论了若干常见的房间压力及通风柜控制方案和误区,并提出了可行的解决方案.     

Effect of cross current due to worker's arm movement on local exhaust ventilation hood

The effect of cross drafts caused by a worker's arm movements on the capture efficiency of a local exhaust ventilation hood was examined in a laboratory. The performance of the local exhaust hoods (rectangular type and slot type) and the transportation of gaseous contaminants from an emission source to the breathing zone were studied by means of the tracer gas method. Acetone vapor was used as a tracer gas. The worker's arm movement was simulated by a dummy worker and a moving forearm model. The results suggest that a worker's arm movements disturb the exhaustion efficiency and may lead to exposure or leakage from a hood according to exhaust velocity.     

Arc Air Gouging: The Hazards and Their Control

Tests have been carried out on the Arc Air Gouging Process toassess the effectiveness of exhaust ventilation systems andprotective equipment against fume and noise. The measures aredescribed in some detail. The results show that adequate protectioncan be achieved by making use of an exhaust booth with a facevelocity of 300 fpm. Investigation into the efficiency of anair fed welding visor showed that it reduced exposure to particulatefume by about 80 per cent and could thus find use in workshopsand semi-confined spaces (coupled with local exhaust ventilation).Measurements of the noise generated confirmed the existenceof a serious hazard to hearing but the use of certain ear defenderscan provide the necessary protection.     

某汽车胶管配件公司涂胶车间局部机械排风系统改造介绍及效果评价

目的 介绍某汽车胶管配件公司涂胶车间局部机械排风系统改造经验及效果, 为今后改善类似作业环境提供参考。
方法 对涂胶车间涂胶机设置的局部排风罩的选择、设计、安装情况进行现场调查; 按照《排风罩的分类及技术条件》(GB/T 16758-2008)规定的方法对排风罩的管道风速、罩口风速、控制距离及控制点风速进行现场测量, 分析排风系统设计问题并进行整改; 对改造后的涂胶机局部排风罩再次进行评价, 确认改造效果。
结果 该企业原先设置的涂胶机局部排风罩不完全合理, 结合车间职业接触情况对局部机械排风系统进行管路集中整合, 减少排风管路分支并对控制距离、排风罩扩张角进行整合改造。改造后控制距离、罩口风速、控制点风速以及空气动力学均满足《简明通风手册》以及《局部排风设施控制风速检测与评估技术规范》(AQ/T 4274-2016)的相关要求, 作业场所职业病危害因素浓度均符合国家职业接触限值的要求。
结论 局部机械排风系统的正确设计、安装及使用可有效提高控制效果。管道风速、罩口风速、控制距离以及控制点风速都会影响局部排风罩的实际控制效果; 罩口围挡可提高局部排风罩的控制效果。