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W501 – INTERNATIONAL MODULE: MEASUREMENT OF HAZARDOUS SUBSTANCES INCLUDING RISK ASSESSMENT
W501 –国际模块：有害物质测量，包括风险评估
ANSWERS TO OVERNIGHT REVISION QUESTIONS – DAY 4
复习问题答案–第4天
1. Whole of air or grab sampling – constant concentrations or for identification of peaks or identification of unknowns.2. Midget impingers, gas wash bottles and fritted glass bubblers can suffer from the following limitations:
· Collection efficiencies – bubble size, number of bubbles, volume of liquid, reaction rate and flow rate
· Need to keep upright
· Awkward to use for personal sampling
3. Adsorption is the technique where by the gas or vapour is collected by passing it over and retained on the solid surface of the solid sorbent media.
4. · Activated charcoal – organic vapours
· Silica gel – polar substances
· Porous polymers – pesticides
· Florisil – PCBs
· Polyurethane foam – pesticides and PNAs
· Thermal desorption tubes
5. Breakthrough occurs when the sorbent tube has become saturated and material passed through the collection bed without being retained. This is said to occur (NIOSH) when the concentration in the backup section excess 20% of the concentration in the front section.
6. Factors affecting breakthrough include:
· Sampling rates too high
· Concentrations too high
· Incorrect sorbent
· Sample volatility – sample migration
7. 20 – 200 mL/minute
8. See section9.5 of the Student Manual.
9. Fick’s Law.
10. Advantages – Devices are lightweight and easy to use and do not require use of a pump, batteries or air flow calibration.
Limitations and Disadvantages – Cannot be used for everything (gravimetric, low vapour pressure organics and reactive compounds), sampling rate supplied by manufacturer, some have a backup section, issues with low or excessive wind speeds.
11. Some of the advantages of direct reading instruments include:
· Where immediate data is needed
· Personal exposure monitoring
· Help develop comprehensive evaluation programmes
· Evaluate effectiveness of controls
· Emergency response
· Confined space
· For difficult to sample chemicals
· Multi sensors/multi alarms
· Stationary installations for both a record of exposure levels and when connected to an alarm to indicate hazardous levels
· Fit testing
· Video monitoring etc.
12. Disadvantages and limitations of direct reading instruments include:
· Often costly to purchase
· Need for frequent and regular calibration
· Lack of specificity
· Effect of interferences
· Cross sensitivity
· Need for intrinsically safe instruments
· Battery life
· Sensors (finite life, poisoning, lack of range)
13. Indicator tubes, infrared analysers, flame ionisation detectors, photoionisation detectors.
14. Liquid impinger, diffusion badge, treated filters and paper tape monitor.
15. Some of the advantages of direct reading colorimetric tubes include:
· Relatively inexpensive and cheap to use
· Wide range of gases and vapours
· Immediate results
· No expensive laboratory costs
· Can be used for spot checks
The limitations include:
· Interferences from other contaminants
· Need to select correct tube and correct range of tube
· Cross sensitivities can be an issue
· Correct storage requirements (some tubes require special storage procedures)
· Limited shelf life of tubes / 1. 空气或抓取法取样全过程——浓度保持不变，或用于明确峰值或其它位置信息。
2. 微型冲击式检尘器，洗气瓶和多孔玻板吸收管存在如下限制：
· 收集效率——气泡的大小，气泡的数量，液体体积，反应速度和流速
· 需要保持直立
· 不适合个人采样
3. 吸收是一种收集通过和保留在固体吸附剂介质固体表面上的气体或蒸汽的技术。
4. · 活性炭 - 有机蒸汽
· 硅胶 - 极性物质
· 多孔聚合物 - 农药
· 弗罗里硅土 - 多氯联苯
· 聚氨酯泡沫 - 杀虫剂和肽核酸
· 热脱附管
5. 当吸附管趋于饱和，通过收集床的材料无法保留，则会穿透。NIOSH规定，当备份段中的浓度超过前段浓度的20%时，则会穿透。
6. 影响穿透的因素包括：
· 采样率过高
· 浓度过高
· 吸附剂不当
· 样本不规定——样本移动
7. 20 – 200 mL/分钟。
8. 请参阅学生手册第9.5节。
9. 菲克定律。
10. 优势 - 设备重量轻，易于使用，不需要使用泵，电池或进行空气流速校准。
局限性和劣势-不是万能的（有重量，低蒸汽压的有机物和活性化合物限制），需要采用制造商提供的取样速率，某些具有备用部分，存在风速过高或过低的情况。
11. 直读式仪器的优势包括：
· 可提供直接数据；
· 可提供个人接触监测
· 可帮助制定全面的评估程序
· 可对控制率的有效性进行评估
· 可提供应急响应
· 有密闭空间
· 适用于采样有难度的化学物质
· 有多个传感器/多警报器
· 提供接触程度记录的固定装置，以及与报警器连接显示危险程度记录固定装置
· 可提供适合性检验。
· 可提供视频监控等。
12. 直读式仪器的劣势或限制包括：
· 售价高
· 需要频繁和定期校准
· 不具备专一性
· 容易受到干扰的影响
· 交叉灵敏度
· 需要本质安全型仪器
· 电池寿命补偿
· 传感器（寿命有限，中毒，范围小）
13. 指示管，红外分析仪，火焰离子化检测器，光化电离检测器。
14. 液体采集器，扩散标记，已处理过滤器和纸带显示器。
15. 直读式比色管的优势包括：
· 使用相对便宜
· 适用的气体和蒸汽范围广
· 提供直接结果
· 没有昂贵的实验室成本
· 可用于抽查
劣势包括：
· 会受其他污染物的干扰
· 需要选择正确的比色管和正确的范围
· 交叉灵敏度也是问题
· 需要适当存储（有些比色管需要特殊存储）
· 比色管保质期有限