Page 77 - Plant design and economics for chemical engineers

GENERAL DESIGN CONSIDERATIONS 59
effects of overpressure on personnel and equipment. To use the available
information, it is necessary to equate the energy of the explosion in terms of
equivalent quantities of TNT as discussed earlier. The explosive yield data are
usually scaled in terms of L/M%%, where L is the distance from the blast
center and M is the equivalent yield in terms of mass of TNT. Even though
present attempts in using this scaling parameter are rather crude, they do
provide reasonable guidelines for locating process equipment and control facili-
ties.?
It becomes clear that the chances a single fire or explosion will spread to
adjoining units can be reduced by careful plant layout and judicious choice of
construction materials. Hazardous operations should be isolated by location in
separate buildings or by the use of brick fire walls. Brick or reinforced concrete
walls can serve to limit the effects of an explosion, particularly if the roof is
designed to lift easily under an explosive force.
Equipment should be designed to meet the specifications and codes of
recognized authorities, such as the American Standards Association, American
Petroleum Institute, American Society for Testing Materials, Factory Mutual
Laboratories, National Fire Protection Association, and Underwriters’ Labora-
tories. The design and construction of pressure vessels and storage tanks should
follow API and ASME codes, and the vessel should be tested at 1.5 to 2 or more
times the design pressure. Adequate venting is necessary, and it is advisable to
provide protection by using both spring-loaded valves and rupture disks.
Possible sources of fire are reduced by eliminating all unnecessary ignition
sources, such as flames, sparks, or heated materials. Matches, smoking, welding
and cutting, static electricity, spontaneous combustion, and non-explosion-proof
electrical equipment are all potential ignition sources. The installation of
sufficient fire alarms, temperature alarms, fire-fighting equipment, and sprinkler
systems must be specified in the design.

Personnel Safety
Every attempt should be made to incorporate facilities for health and safety
protection of plant personnel in the original design. This includes, but is not
limited to, protected walkways, platforms, stairs, and work areas. Physical
hazards, if unavoidable, must be clearly defined. In such areas, means for egress
must be unmistakable. All machinery must be guarded with protective devices4
In all cases, medical services and first-aid must be readily available for all
workers.

tK. Gugan, “Unconfined Vapor Cloud Explosions,” Gulf Publishing Company, Houston, TX, 1979.
$A general requirement for safeguarding all machinery is provided in Section 212 of the Occupa-
tional Safety Standard for General Industry (OSHA Standards, 29 CFR 1910): .