Barco Njord, Installation Manual

Page: 208 / 232

R5913593 /01 Njord 208
18.4 HD for fully enclosed projection systems
HD
Hazard Distance (HD) is the distance measured from the projection lens at which the intensity or the
energy per surface unit becomes lower than the applicable exposure limit on the cornea or on the
skin. The light beam is considered (to be) unsafe for exposure if the distance from a person to the
light source is less than the HD.
Restriction Zone (RZ) based on the HD
The projector is also suitable for rear projection applications; projecting a beam onto a defuse coated
projection screen. As displayed in Image 18
– 3 two areas should be considered: the restricted enclosed
projection area (RA) and the observation area (TH).
RA TH
sw
PD
HD
DIFFUSE
s
w
RZ
s
w
s
w
PR
HD
REFLECTION
RESTRICTED
AREA
R
E
S
T
R
IC
T
E
D
A
R
E
A
Image 18 – 3
RA Restricted Access location (enclosed projection area).
PR Projector.
TH Theater (observation area).
RZ Restriction Zone.
PD Projection Distance.
SW Separation Width. Must be minimum 1 meter.
For this type of setup 3 different HD shall be considered:
• HD as discussed in “ HD in function of modifying optics ” , page 209, relevant for intrabeam exposure.
• HD
reflection
: the distance that has to be kept restrictive related to the reflected light from the rear projection
screen.
• HD
diffuse
: the relevant distance to be considered while observing the diffuse surface of the rear projection
screen.
As described in “ HD in function of modifying optics ” , page 209, it is mandatory to create a restricted zone
within the beam areas closer than any HD. In the enclosed projection area the combination of two restricted
zones are relevant: The restricted zone of the projected beam toward the screen; taking into account 1 meter
Separation Width (SW) from the beam onward. Combined with the restricted zone related to the rear reflection
from the screen (HD
reflection
); also taking into account a 1 meter lateral separation.
The HD
reflection
distance equals 25% of the difference between the determined HD distance and the projection
distance to the rear projection screen. To determine the HD distance for the used lens and projector model see
chapter
“ HD in function of modifying optics ” , page 209.
HD
reflection
= 25% (HD – PD)
The light emitted from the screen within the observation shall never exceed the RG2 exposure limit,
determined at 10 cm. The HD
diffuse
can be neglected if the measured light at the screen surface is below 5000
cd/m² or 15000 LUX.
Risk group 3 Safety