Instruments Used in Safety Laboratories

The totality of the heat released by the reaction under study must be converted into heat accumulation, that is, into a temperature increase, which can be measured. This is obtained by eliminating the heat exchange with the surroundings, achieving adiabatic conditions  

Adiabatic conditions may be achieved either by a thermal insulation or by an active compensation of heat losses. Examples are the Dewar calorimeter, achieving a thermal insulation [2-4] or the Accelerating Rate Calorimeter (ARC) [5] or the Phitec [6], using a compensation heater avoiding the heat flow from the sample to the surroundings. These calorimeters are especially useful for the characterization of runaway reactions. 

In this case, the totality of heat released by the reaction under study is transferred to the surroundings  

In this category of calorimeters, we find the isothermal calorimeters and the dynamic calorimeters where the temperature is scanned using a constant temperature scan rate. The instrument must be designed in such a way that any departure from the set temperature is avoided and the heat of reaction must flow to the heat exchange system where it can be measured. The instrument acts as a heat sink. In this family we find the reaction calorimeters, the Calvet calorimeters [7], and the Differential scanning calorimeter (DSC) [8], 

In these calorimeters, the temperature of the surroundings is controlled and maintained constant or scanned. So the temperature of the sample is allowed to vary as well as the heat flow to the surroundings. Hence the results are more difficult to evaluate than with the techniques described above. Therefore these instruments are often semi-quantitative. 

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In this chapter, some of these instruments are reviewed. A first section is a general introduction to calorimetric principles. In a second part, some methods commonly used in safety laboratories are reviewed. This is not an exhaustive review of such instruments, but based only on the experience of the author. 

The EU issued a Directive in 1998 covering the protection of health and safety of workers from the risks related to chemical substances [11]. In the UK there is a legal requirement based on this Directive, namely Statutory Instrument 2002/2677 [12]. The UK Health and Safety Executive issues guidance on implementing COSHH (Control of Substances Hazardous to Health) Regulations. Each laboratory is required to assess the risk associated with each chemical (or generic families of chemicals) in use in that laboratory. This risk is assessed according... 

Lasers are commonly used in the laboratory, although in many instruments, most lasers are embedded in instrumentation and are therefore shielded or protected by optical barriers and interlocks that, when functioning properly, prevent accidental exposure. Care must be exercised when performing maintenance or when changing samples in such instruments. In this section we provide basic information on laser safety and hazards (Refs. 1 to 3). This is by no means exhaustive nor is it meant to substitute for an understanding of the specific safety requirements of instrumentation, or applicable law or regulations. The special case of common laser pointers has received considerable attention recently and is treated separately. We note that as of 2007, the general practice in the United States is to use the lEC definitions. 

There is more to a laboratory than work benches and the instruments mounted on them. Free-standing equipment must also be considered. This includes refrigerators, safety storage cabinets for chemicals, safety shower, desk space, typewriter stand or computer terminal, or any other equipment that is not bench-mounted. File cabinets, which are real space-robbers, must not be forgotten. In one laboratory, much space was saved by placing two-drawer file cabinets beneath the large table used for sorting samples. 

Safety glasses must be worn in the laboratory at all times. Material safety and data sheets should be read prior to the start of the experiment. All chemicals should be considered hazardous from a standpoint of flammability and toxicity. Appropriate safety gloves must be worn when using organic solvents so that no skin contact is permitted. Care must be taken to use organic solvents either in a well-ventilated area or in a hood. Avoid breathing the fumes or sources of electrical sparks. The GPC instrument, including solvent reservoir and waste container, should be vented to a fume hood or other exhaust system. 

A more expensive alternative is to use standard AutoAnalyser type systems, based on multichannel peristaltic pumps, to pump samples and reagents and/or diluents at the desired rates to give automatic mixing at the desired ratio. Flame photometric detectors have been used for many years with AutoAnalysers, especially in clinical laboratories. Curiously, in the past, this approach has less often been routinely used in environmental analytical laboratories employing flame spectrometry, perhaps because an attractive feature of flame spectrometry is the speed of response when used conventionally. Over the past few years, however, there has been an increasing tendency towards fully automated, unattended operation of flame spectrometers. This undoubtedly reflects, at least in part, the improvements in safety features in modern instruments, which often incorporate a comprehensive selection of fail-safe devices. It also reflects the impact of microprocessor control systems, which have greatly facilitated automation of periodic recalibration. 

The introduction of a reaction to the pilot plant often proceeds without determining the chemical hazards involved with the scale up process. The reasons for this vary. In cases where a hazards evaluation laboratory is not available, it is the responsibility of the development chemist to assure the safety of the reaction. The development chemist may not be familiar with hazard evaluation techniques, and the instrumentation used to evaluate a reaction for safety may not be readily available. 

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