Working with Compressed Gases

Nowadays every university laboratory is doubtless supplied with steel cylinders in which the most important gases in common use are stored in the compressed state. 

In the laboratory all cylinders should befitted with reducing valves, for the maintenance of which an assistant should be responsible. The use by itself of the simple valve in the head of the cylinder makes regulation of the gas stream difficult and invariably leads to waste. 

For all gases (chlorine included) the so-called conical valve of aluminium bronze can be used. It can be made cheaply by any skilled mechanic (Fig. 28). 

Ordinary laboratory apparatus cannot be used with gas from a cylinder for carrying out reactions under pressure in a closed system. For example, if it is desired to leave a reaction solution under pressure 

1 After use the connection between steel cylinder and wash-bottle should always be broken so as to prevent sucking back of the sulphuric acid. 

---

It has been known for nearly eighty years that compressed gases can dissolve solids to give mixtures in which the concentration of the solid component is very large compared to that in the pure saturated vapor. Nevertheless, this effect has not always been appreciated by those working with compressed gases in other fields. Here we discuss briefly two types of measurement in which the enhanced concentration of the second component may have introduced unsuspected errors. 

With such a direct gas displacement pump, the delivery of liquid is virtually pulseless. The liquid pressure is controlled by the pressure controller on the gas supply line. The pressure is limited by the strength of the tank and by the maximum pressure of the gas supply (usually 200 atm, sometimes up to 250 atm). Some commercial direct gas displacement pumps, however, have a maximal pressure of about 100 atm, owing to the safety aspects of working with compressed gases at higher pressures. 

For commonly used laboratory gases, it is prudent to consider the installation of in-house gas systems. Such systems remove the need for transport and in-laboratory handling of compressed gas cylinders. Chapter 5, section H, provides additional information on working with compressed gases in the laboratory. 

In section 5.D, additional special procedures are presented for work with highly toxic substances. How to determine when these additional procedures are necessary is discussed in detail in Chapter 3, section 3.C. Section 5.E gives detailed special procedures for work with chemicals that pose risks due to biohazards and radioactivity section 5.F, flammability and section 5.G, reactivity and explosibility. Special considerations for work with compressed gases are the subject of section 5.H. 

H WORKING WITH COMPRESSED GASES 5.H.1 Chemical Hazards of Compressed Gases... 

Because of its high acute toxicity, arsine should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional practices for work with compounds of high toxicity (Chapter 5.D), flammability (Chapter 5.F), and for work with compressed gases (Chapter 5.H). In particular, cylinders of arsine should be stored and used in a continuously ventilated gas cabinet or fume hood. Local fire codes should be reviewed for limitations on quantity and storage reqnirements. 

Chlorine should be handled in the laboratory using the "basic prudent practices" described in Chapter 5.C, supplemented by the procedures for work with compressed gases discussed in Chapter 5.H. AU work with chlorine should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Cylinders of chlorine should be stored in locations appropriate for compressed gas storage and separated from incompatible compounds such as hydrogen, acetylene, ammonia, and flammable materials. 

Storage and Handling Oxygen should be handled in the laboratory using the "basic prudent practices" described in Chapter 5.C, supplemented by the procedures for work with compressed gases found in Chapter 5.H. 

Description of hazard. Water plant operators, associated maintenance staff, and laboratory technicians are often required to work with compressed gases in treatment plants, maintenance facilities, and associated laboratories. Numerous potential physical and health hazards are associated with compressed gases such as propane, oxygen, nitrogen, argon, chlorine, ammonia, and compressed air. Compressed gases can be stored in cylinders (Figure 6-6), portable tanks, or stationary tanks. 

---