Page 158 - Offshore Electrical Engineering Manual

CHAPTER
14
Offshore Lighting

INTRODUCTION
If those readers unfamiliar with offshore conditions imagine being woken up in the
top bunk of a pitch black cabin by a strange alarm sounding, possibly accompanied
by the sound and shock of explosions, they will appreciate that every aid to orienta-
tion and escape is vital.
Particularly since the Alexander Kielland disaster some years ago, when an
accommodation semi-submersible capsized at night with heavy loss of life, offshore
engineers have been aware of the importance of good escape lighting. Visual infor-
mation from our surroundings is of vital importance in any environment if comfort
and safety are to be maintained. In the offshore environment, bad lighting can very
easily lead to accidents and injury and should be considered as an essential topic of
any design safety audit. Since the time of writing of the first revision of this book, a
few years after the Piper Alpha disaster (1988), the Prevention of Fire, Explosion
and Emergency Response Regulations have come into force in UK waters. These
regulations, among other issues, require platform alarms and emergency lighting to
meet minimum standards for safe evacuation. The regulations not only cover the
requirements for illumination of escape routes, but also illumination of any safety
equipment required to be operated during an emergency.

LIGHTING CALCULATIONS
POINT SOURCES
In the visible wavelength range, radiant flux or electromagnetic radiation is consid-
ered to have a luminous flux associated with it. This luminous flux is a measure of
human visual response, and a point source of light emitting a uniform intensity of
1 cd in all directions emits a total flux of 4π lumen (lm).
The illumination effect of a point source of light is shown in Fig. 2.14.1. A point
source S, emitting luminous flux in all directions, illuminates a plane surface P. The
flux dΦ intercepted by an element of area dA on P is the flux emitted within the solid
angle dω subtended at the source by the element dA, assuming no absorption of light
takes place in the space between the source and the surface. The term dΦ/dω is called
the luminous intensity I of the source of the direction being considered. The accepted

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