Fumes monitoring

For some hood types, measurements usually seen as indirect method, are used to measure the hood s performance to determine regulatory compliance. For example, regulations specify minimum and maximum face velocities for laboratory fume hoods and static pressure (negative) inside enclosed hoods. Continuously monitoring instruments can be connected to alarms that sound when the measurement is outside the specified limits. 

Figure 13.37 is a plot of relative roof monitor opacity as a function of fume hood suction. 

The precise nature of the test will depend on the particles being controlled. The simple observation tests carried out by Tyndall lights and smoketubes will suffice for the majority of dust and fume systems. It is only where the contaminants are listed and known to be dangerous that special testing needs to be done. This work requires onsite monitoring of the workplace using air samplers and the expert services of an industrial hygienist. 

The ventilation system must be able to carry away hazardous fumes that may form during normal work. Monitoring the laboratory atmosphere for such fumes while work is in progress is not only advisable, but may even be required by law. Monitoring must be repeated whenever new fume-producing procedures are introduced or any time modifications are made to the ventilation system. Local health authorities should be contacted about... 

Safety note. An electrochemical HCN detector (Micro III G203, GfG-Gesellschaft fiir Geratebau mbH, Dortmund, Germany) was placed in the fume hood for continuous monitoring. 

For monosulfonation of PPh3 the reaction mixture can be heated for a limited time [1-3] while multiple sulfonation is achieved hy letting the solution stand at room temperature for a few days [4-10], In this simplest way of the preparation several problems may arise. Under the harsh conditions of sulfonation there is always some oxidation of the phosphine into phosphine oxide and phosphine sulfides are formed, too. Furthermore, selective preparation of TPPMS (1) or TPPDS (2) requires optimum reaction temperature and time and is best achieved by constantly monitoring the reaction by NMR [10] or HPLC [7]. Even then, the product can be contaminated with unreacted starting material. However, 1 can be freed of both the non-sulfonated and the multiply sulfonated contaminants by simple methods, and in the preparation of TPPTS (3) contamination with PPh3, 1 or 2 is usually not the case. Direct sulfonation with fuming sulfuric add was also used for the preparation of the chelating diphosphines 34-38, 51, 52. 

Temperature and humidity is controlled to minimize evaporation of reagents and to keep performance of electronic equipment optimal. Ventilation is adequate for the removal of noxious fumes and odors. Formaldehyde and xylene vapor concentrations must be below maximum permissible levels. For formaldehyde, this level is 0.75 ppm for an 8-h time-weighted average, or 2.0 ppm for a 15-min short-term exposure. For xylene, the level is 100 ppm for an 8-h time-weighted average and 200 ppm for a 15-min short-term exposure. The monitoring of the work area and employees can be performed on a yearly basis. Chemical and biological safety cabinets are checked for proper airflow on a yearly basis. 

The National Institute of Justice has put together multivolume compendiums of instrumentation relevant to chemical and biological weapons detection. However, none of these books contains a critical review of the effectiveness of the technologies. One instrument included in the publication is a portable, handheld, ion mobility spectrometry chemical agent monitor with moderate to high selectivity, but only when used in open spaces, far from vapor sources such as smoke, cleaning compounds, and fumes. This would seem to make it useless in the battlefield. Another listed chemical agent monitor has a below 5% false positive rate. With one in 20 false positives, no one could reasonably act upon an alarm. 

Field Sampling. An opportunity arose where actual field samples could be analyzed by both the infrared and gas chromatographic methods. At Robins AFB, Georgia, workers were inspecting and repairing the interior and exterior of C-141 aircraft fuel tanks. They were exposed only to JP-4 fuel fumes. Duplicate charcoal tubes or vapor monitors were attached to each worker, one on each lapel. Samples were drawn through the charcoal tubes at 0.20 to 0.26 1pm by portable pumps attached to the worker s belt. Because of slight variations, the total volumes collected for the duplicates were close, but not exactly the same in all cases. Samples were then labeled and shipped to our Laboratory for analysis by both methods. 

Sampling and analysis of several metal fumes were investigated in order to develop a reliable method for monitoring work place atmospheres. Significant results are listed below. 

Figure 28-13 Extraction vessels in a microwave oven that processes up to 12 samples in under 30 min. Each 100-mL vessel has a vent tube that releases vapor if the pressure exceeds 14 bar. Vapors from the chamber are ultimately vented to a fume hood. The femperature inside each vessel can be monitored and used to control the microwave power. [Courtesy CEM Corp.. Matthews. NC.]...

A mixture of benzaldehyde (1.06 g, 10 mmol), ethanedithiol (0.94 g, 10 mmol) and commercial grade cadmium iodide (1.85 g, 5 mmol) was mixed thoroughly in an Erlenmeyer flask and placed in a commercial microwave oven operating at 2450 MHz frequency. The whole operation was carried out in a fume-cupboad. After irradiation of the mixture for 75 s (monitored by TLC) it was cooled to room temperature and extracted with dichloromethane. Evaporation of the solvent gave almost pure products. Further purification was achieved by column chromatography on silica gel using chloroform-petroleum ether (1 5) as eluent. 

Small Quantities. Wear butyl rubber gloves, laboratory coat, and eye protection. Work in the fume hood. Prepare a dilute (5%) aqueous solution of methylhydrazine by adding slowly to the appropriate volume of water. For each 1 g of methylhydrazine, place 41 mL (about 25% excess) of household laundry bleach (5.25% sodium hypochlorite) into a three-necked, round-bottom flask equipped with a stirrer, thermometer, and dropping funnel. Add the aqueous methylhydrazine dropwise to the stirred hypochlorite solution, monitoring the rate of addition by rise in temperature. The temperature is maintained at 45-50 ,C and addition takes about 1 hour. Continue stirring for 2 hours until the temperature gradually falls to room temperature. The cooled reaction mixture can be washed into the drain.7... 

Small Quantities. Wear eye protection, laboratory coat, and butyl rubber gloves. Work in the fume hood. Add tributylphosphine (10.1 g, 0.05 mol) dropwise while stirring to a 25% excess of hypochlorite (670 mL of laundry bleach or 55 g calcium hypochlorite in 200 mL of water). The temperature of the reaction should be monitored. After addition is complete and the reaction has subsided, filter the solid and package it for disposal by burning. Wash the aqueous solution into the drain.5... 

Caution HCN is a highly toxic, volatile liquid (bp 27 °C) that is also susceptible to explosive polymerization in the presence of base catalysts. It should be handled only in a well-ventilated fume hood and by teams of at least two technically qualified persons who have received appropriate medical training for treating HCN poisoning. Sensible precautions include having available proper first aid equipment and HCN monitors. Uninhibited HCN should be stored at a temperature below its melting point (-13 °C). Excess HCN maybe disposed by addition to aqueous sodium hypochlorite, which converts the cyanide to cyanate. 

By responding to fumes in cooking areas, car parks, laboratories and similar places, gas sensors can be used to control ventilation fans. In industrial situations the sensor can monitor concentrations of carbon monoxide, ammonia, solvent vapours, hydrocarbon gases, ozone etc., and because of the growing consciousness of environmental pollution and the safety aspects of industrial processes the applications will multiply. 

A good practice is to monitor the workspace inside the fume cupboard with a continuous handheld or tabletop chemical agent detector, if such a device is available. There are several models commercially available based on ion mobility, flame photometric, enzymatic, or photoacoustic detection (9). 

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