Page 313 - Offshore Electrical Engineering Manual

300 CHAPTER 3 Environmental Protection

First, exposed items of electrical equipment located in busy thoroughfares such as
walkways, drill decks and laydown areas should be of steel construction or provided
with steel impact protection of some form. No equipment should obstruct walkways.
Overhead equipment such as luminaires and cable tray should not project lower than
2 m (safety helmets add about 100 mm to a person’s height).
Second, the loci of crane loads should be carefully studied so that areas where the
risk of dropped loads is high can be avoided as prospective critical equipment loca-
tions. If high-risk areas are unavoidable, then adequate mechanical protection will
need to be provided, allowing for the shape and kinetic energy of potential dropped
loads.

NOISE CONTROL

It is practically possible to run a platform unmanned and to shut down only for planned
maintenance periods, which would then be the only time when the maintenance crew
would be present. However, equipment reliabilities demand that unplanned outages
be attended to, so noise levels must be limited throughout any installation if it is to
be operated and manned at the same time. Sound levels less than 85 dB (A) should be
the aim of any design, with much lower levels near accommodation areas.

PRIME MOVERS
Generator set procurement specifications must detail the maximum sound power
level acceptable, with frequency spectra if possible. Equipment tests will need to be
witnessed to ensure that the specifications are complied with. However, three main
methods are available to the offshore design engineer to reduce the effects of prime
mover noise offshore:

1. A close fitting acoustic hood can be installed over the engine, usually sized to
fit round the skid on gas turbines. The enclosure sound insulation material must
not absorb fuel, lubricant or coolant, as the enclosure itself must be designed
to contain and extinguish engine fires with the aid of a halon or similar gas
discharge.
2. It is difficult to enclose reciprocating engines in this way without impeding
access for maintenance. Therefore the module housing the engine and genera-
tor may be soundproofed. If acoustic dampers are fitted to ventilation intakes
and exhausts, this has the advantage that generator and radiator fan noise is also
controlled.
3. Modules containing normally running prime movers should be located as far
away from continuously manned areas as possible, although this distance is likely
to be constrained by other limitations such as hazardous areas and air intake and
exhaust positioning. In practice, a combination of all three methods will be used.