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Safety Practices . 21
Calculation of Nominal Hazard Zones for use of Fiber Optic Probe
The following calculations show how to calculate a nominal hazard zone. These calculations
are taken from ANSI Z136.1-1933. A laser safety officer uses these calculations to help
define how to use your Raman probe safely in your environment.
Figure 1 Probe parameters used to calculate the nominal ocular hazard distance
The equation for a focused beam as given here (Figure B5 in ANSI Z136.1-1933) is used to
calculate the nominal ocular hazard distance (NOHD) for the TFOP. The equation is:
2
1
. Π
Φ 4












=
MPE b
f
NOHD
o
o
Where:
f
o
= Probe focal length (cm)
b
o
= Diameter of laser beam incident on probe focusing lens (mm)
Φ
= Total radiant output power of probe (watts)
MPE
=
Maximum permissible exposure (J cm
−2
)
For the TFOP
b
o
is 0.254 cm therefore the above equation can be simplified to give:
2
1
Φ
. 442 . 4






=
MPE
f NOHD
o
For the wavelength range 700–1050 nm the
MPE
for a 10 second exposure can be calculated
from:
( )
( )
( )
[ ]
4 7 . 0 2
10 10 1 . 10
− −
=
λ
MPE
J cm
−2
Where
λ
is the laser wavelength in micrometers (
µ
m). For example, a laser wavelength of
785 nm (0.785 µ m) will have an
MPE
value of 1.49 x 10
−2
J cm
−2
or 1.49 x 10
−3
W cm
−2
for
a 10 second exposure or longer. Table 3 shows the calculated nominal ocular hazard distance
for 785 nm Raman systems.
Table 3 Nominal Ocular Hazard Distance (NOHD) for 785 nm
Probe focal length / mm NOHD for 100 mW exiting fiber optic probe / cm
7.5 (±10%) 27.3
NOTE: Other focal lengths are available; contact PerkinElmer for details. In particular, the
use of an ultra-long working distance lens adaptor (part number L1320071) provides
a working distance of 25 mm. Where different focal lengths are used, the NOHD
should be calculated accordingly.
b
o
f
o
NOHD