Chemicals fume cupboards

Class I The Class I BSC provides personnel and environmental protection, but no product protection. It is similar in air movement to a chemical fume cupboard, but has a HEPA filter (see Chapter 9) in the exhaust system to protect the environment (Fig. 10.94). In the Class 1 BSC, unfiltered room air is drawn across the work surface. Personnel protection is provided by this inward air velocity as long as a minimum velocity of 0.37 m s" is maintained through the front opening (see the discussion on fume cupboards in Section 10.2.3.3). In many cases Class I BSCs are used specifically to enclose equipment. 

The simplest and most efficient engineering control is the segregation of people from the process and a chemical fume cupboard is an example of this as is the handling of toxic substances in a glove box. Modification of the process is another effective control to reduce human contact with hazardous substances. 

Are there any alternative chemicals which can be used to eliminate hazards (e.g., the use of lithium metaborate fusion rather than hydrofluoric acid as a dissolution procedure) The protocol should include details of any required checks on the control measures to be adopted, and their frequency (e.g., cleaning of protective clothing, washing down of fume cupboards). 

Fume cupboards must be kept free from surplus chemicals and discarded apparatus. If stocks of noxious chemicals which are in frequent use have to be stored in a fume cupboard they should all be assigned to one which is set aside for this purpose and is properly fitted with shelving. Chemicals which are carcinogenic, but the use of which is permitted, are always retained in a main store in specially provided sealed cabinets definitive authorisation is required for their use. 

Some highly reactive chemicals and their dangerous properties are listed below. Those which give off highly corrosive irritant and/or toxic vapours or, if solids, are similarly hazardous in the form of dusts, are marked with an asterisk ( ) and should only be used in fume cupboards. More details concerning the properties of many of these are given in Section 4.2. Specific information on the hazardous properties of individual chemicals is collected in several comprehensive works.8 -11... 

Inhalation (into the lungs). This is a more common pathway for the absorption of toxic chemicals these may be in the form of gases, vapours, dusts or mists. All toxic powders, volatile liquids and gases should only be handled in efficient fume cupboards. The practice of sniffing the vapours of unknown compounds for identification purposes should be conducted with caution. 

It is recommended that experiments with explosive chemicals not be conducted in the confinement of standard fume cupboards, with shatterable front and side panels, but on the open bench behind anchored polycarbonate blast screens. Even light top cover is found much to increase lateral blast effects. Specially designed laboratories are, of course, much preferable for such experiments. 

Toughened glass used in fume cupboard windows can occasionally shatter explosively when edge defects are present. Although a physical hazard, it is possible to imagine it triggered by a small chemical explosion, which could even amplify the... 

A second portion of soil, or the soil fraction from the dichloromethane extraction (after drying in a fume cupboard for approximately lh), is extracted with distilled, deionized water in the manner described above for the dichloromethane extract. Usually, sonication is avoided because it may reduce recoveries of the polar CWC-related chemicals by creating new active sites for analytes in the soil. The extracts are centrifuged, filtered, and combined and the pH is determined. 

CWC-related chemicals must be handled with great care. Persons handling toxic chemicals must be specially trained for the work. When toxic samples are handled, decontamination solution, protective masks, and autoinjectors of nerve agent antidotes must always be available, and no one must ever work alone. Individual protective gear such as laboratory coats, chemically resistant protective gloves, and safety goggles are essential during sample preparation. Toxic samples must always be prepared in a fume cupboard. 

The work area should be kept tidy to enable safe sample preparation. It is a good idea to use trays in the fume cupboard. These are easy to clean and decontaminate after the work is finished and also, they contain any spillage of chemicals. 

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). 

The area which constitutes an individual bench wiU vary considerably from one lab to another. In our view all procedures involving organic chemicals should be carried out in an efficient fume cupboard. This implies that each full-time wo er in an organic chemistry lab permanently requires at least one metre of fume cupboard space. However, in practice it is often the case, particularly in academic labs, that much less fume cupboard space is actually provided, and fume cupboards may be communal. In this chapter the term bench will refer to the space occupied by an individual worker and it wiU be assumed that this space incorporates an adequate area of fume cupboard, where all reactions are carried out. 

Use a fume cupboard for hazardous chemicals. Make sure that it is working and then open the front only as far as necessary many fume cupboards are marked with a maximum opening. 

Wear gloves for toxic, irritant or corrosive chemicals and carry out procedures with them in the fume cupboard. 

Clean the plates in the fume cupboard by wiping them with a tissue soaked in DCM, stand them on filter paper or tissue paper to allow the solvent to evaporate and put them in the desiccator. Allow the DCM to evaporate from the tissue swab and dispose of it in the chemical waste. 

Any increase in pressure, whatever the cause, may be sufficient to blow ground glass joints apart, or to cause some part of the line to explode, usually that part of the line with the greatest diameter of tube. Safety spectacles should always be worn by everyone in the vicinity of a glass vacuum line. When the chemicals handled in any vacuum line are known to be poisonous, the line should be in a fume cupboard. Pressure release devices such as mercury manometers with one limb open to the atmosphere, or "0"-ring cup joints, should be included in ail sections of a vacuum line which may be subject to excessive internal gas pressures. 

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