b.
A pressure vessel changes dimensions in response to pressure
variations. Adjoining chambers under different pressures experience
different dimensional changes. Varying pressures independently in attached
chambers will produce unusual stress patterns. The chamber design must
provide for meeting all possible pressure and temperature loading conditions.
c.
Many penetrations are required in a wide range of sizes. In
particular, the doors for personnel entrance are very large in proportion to
the size of the chamber. Service locks and viewports are large and present
special problems. The design must provide the necessary vessel
reinforcements at each of the penetrations. In addition, human engineering
should be applied to the location of doors, viewports, internal piping,
furnishings and hardware, and particularly to the accessibility of the
emergency equipment, so that the occupants can exist and function in a
reasonably hazard-free manner.
d.
A major consideration in the design of a hyperbaric pressure
vessel is to reduce, to the practical minimum, the possibility of a
catastrophic leak while maintaining the desired operational features of the
facility. In the usual operational mode, the pressurization and
depressurization of the atmosphere is done at a slow controlled rate. A
sudden uncontrolled release of the pressurized atmosphere, such as caused by
a chamber rupture or large leak, could prove fatal to personnel occupying the
pressure chamber and could possibly present a considerable hazard to the
chamber operators. Thus, great emphasis must be placed upon the use of
proper design, materials, fabrication, quality assurance, inspection, and
testing of hyperbaric chambers. Proper design includes the use of modern
analytical and experimental stress analysis, metallurgy, joining techniques,
and destructive and nondestructive testing procedures.
e.
The rules, regulations, and requirements for the design,
fabrication, inspection testing and identification of hyperbaric pressure
vessels are provided in great detail in the ASME Boiler and Pressure Vessel
Code (ASME code), Section VIII, Pressure Vessels, Divisions 1 and 2 (See
Reference 1, ASME Boiler and Pressure Code, 1980). If the Hyperbaric
Facility is to be man-rated, Section VIII of the Code must be supplemented by
ANSI/ASME PVHO 1, Safety Standards for Pressure Vessels for Human Occupancy
(Reference 2).
f.
Within the constraints of these mandatory codes, a full range of
facilities can be designed and built. Relatively simple pressure vessels
such as conventional 2 lock recompression chambers, animal and equipment test
vessels and various moderate pressure, liquid- and gas-containing vessels are
usually made in accordance with Division 1. This Division requires only a
cursory determination of stress conditions and then requires the designer to
use certain specified "acceptable" geometries. The lack of knowledge
concerning the actual stress conditions is compensated for by imposing a high
factor of safety upon the nominal stresses that are calculated. For the
above classes of pressure vessels, adherence to the requirements of Section
VIII, Division 1, results in adequate and safe pressure vessels. For the
more complex pressure vessels such as hyperbaric research facilities and
vessels for pressures on the order of 1000 psi
and higher Division 2 will usually be used. The procedures of Division
2 are sometimes referred to as Design by Analysis. Regardless of chamber
complexity and variability of the material properties, a rational design
procedure can be applied to pressure chambers
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