532-Permit To Work / 748
P
er
m
it to
W
or
k
BOS-PRD-03.900902
4
.
7
.1
V
e
n
til
a
ti
n
g
an
e
nc
lo
s
e
d
s
p
ac
e
No enclosed space
shall
be entered unless forced ventilation has been conducted and the atmosphere
tested safe for entry:
x
Natural ventilation is not adequate to achieve safe atmosphere levels;
x
Spaces being ventilated
shall
have a minimum, of two openings to ensure that air being dispelled is
done so effectively. If not the ventilation process will not be effective;
x
As a guide, for any ballast or any tank that contain or has contained only potable water, the volume
of air in the space
shall
be changed at least three times prior to entry. For example, a space with a
volume of 100m
3
shall
have 300m
3
of air exchange. With a blower capacity of 100m
3
/hour, the
space
shall
be ventilated for at least three hours;
x
For all tanks that contain and/or have contained hazardous substances and hydrocarbons, proper
ventilation 24 hours prior to cleaning
shall
be performed and ventilation
shall
reach the confined
space bottom;
x
While personnel remain in a tank or compartment, ventilation
shall
be continuous and frequent
atmosphere tests
shall
be taken.
W
he
n
ve
n
til
a
ti
n
g
s
p
ac
e
s
suc
h
as
c
h
a
i
n
lo
ck
er
s
and
voi
d
s
p
ac
e
s w
here there
w
ill
b
e r
us
ti
n
g
o
f
s
teel
w
or
k,
o
x
y
g
e
n
level
s
i
n
the
s
p
ac
e
w
ill
b
e
c
o
ns
i
d
er
ab
ly re
duc
e
d
. Level
s
o
f
le
ss
th
an
10%
w
ill
caus
e
i
mm
e
d
i
a
te
d
e
a
th.
4
.
7
.
2 T
e
s
ti
n
g
the
a
t
m
o
s
p
here
Hydrocarbon Vapour
No more than 1% LEL.
Oxygen
No lower than 20% and no higher than 21% by volume.
Carbon Monoxide (Co)
Lower than 35 ppm.
Hydrogen Sulphide (H2S)
Lower than 10 ppm.
The enclosed space
shall
only be entered after the following safety measures have been taken:
x
The competent person responsible for operation and maintenance of the multi-gas detector
shall
ensure that the equipment in use is certified as calibrated and checked;
x
Where appropriate the competent person
shall
calibrate the equipment before use;
x
Representative samples of a cross section of the atmosphere in the space
shall
be taken at various
levels (high, low and medium) using an extension probe device through as many deck openings as
is practical. Tests
shall
only be carried out from outside the space;
x
When tests are being carried out, ventilation
shall
be stopped and a period of about 10 minutes
allowed to lapse before readings are taken;
x
Testing
shall
be repeated at regular intervals (about every hour) during the period personnel are
within the space and recorded on the PTW;
x
A full range of tests
shall
be undertaken if there is any suspicion of changing circumstances or if
there has been a break in the work;
x
When tests have shown a tank or compartment to be safe for entry, pockets of gas
shall
always be
suspected, and regeneration of hydrocarbon gas
shall
always be considered possible, even after
loose scale has been removed;
x
Use of personal detectors capable of continuously monitoring the presence of hydrocarbon vapour,
the oxygen content of the atmosphere, and, if appropriate, toxic vapour,
shall
be carried by
personnel in the space at all times;
x
If considered necessary, request additional assistance when testing atmosphere, such as from a
Chemist or other professional body.
Version 04. Original date: 25/05/2012. Version date: 31/12/2014. Valid version only on QMS site. Uncontrolled document when printed.
Procedure prepared by: BOS QHSES Coordinator. Approved by: BOS QHSES Manager. Validated by: BOS Quality Representative.
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532