Boiler and Pressure Vessels Particular Hazards of Note
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Potentially-Explosive Material Safety
There are a number of functional group categories whose presence within a structure is a common indication of explosive potential. Use of reagents containing these functional groups in a high-pressure reactor is contraindicated. Some of these groups are:
- Metal acetylide
- Amine oxide
- Diazo and diazonium
- Nitrate, nitrite, nitro and nitroso
For an excellent reference on chemical safety related to the use of pressure vessels, see Safety in the Operation of Laboratory Reactors and Pressure Vessels
Overloading of a pressure vessel is a significant hazard. Dangerous pressures can develop suddenly and unexpectedly when a liquid is heated in a closed vessel if adequate head-space is not available to accommodate the expansion of the liquid. This is particularly true of water and aqueous solutions, whose volume may increase up to a factor of three when heated to 374oC. A vessel must never be filled to more than three-fourths of its available free space. Frequently, the maximum fill level must be reduced even more to ensure safe operation. If a table of volume multipliers is available for the solvent in use, use this data to calculate to maximum allowable loading using the formula:
Max. Loading Volume = (0.9)(Vessel Volume)/Volume Multiplier at Max. Temp.
Volume multiplier tables for water can be found in “Steam Tables: Thermodynamic Properties of Water Including Vapor, Liquid, and Solid Phases/With Charts” Joseph H. Keenan, Frederick G. Keyes, Philip G. Hill, Joan G. Moore, Krieger Pub Co, 1992, as well as in the Parr Instrument Company document No. 230M: “Safety in the Operation of Laboratory Reactors and Pressure Vessels” – see above.
Limitations of the Material of Construction
Pressure vessels of identical design but of different materials of construction will have vastly different pressure and temperature limits, as well as differing corrosion resistance towards solvents and reagents (acids and bases in particular). The material of construction of the vessel must be known and its limitations understood before initiating an experiment. For commercial reactor vessels, the user’s manual and other documentation is an excellent resource for this information.
Robin McCall-Miller, Occupational Safety Program Manager