A WORKING ENCLOSURE

ENCEINTE DE TRAVAIL

English Abstract

A working enclosure adapted to provide a clean air zone within a potentially hazard environment such as an oil storage tank, the enclosure comprising a canopy (10) supported by a frame (11) and having a skirt (12) to be held in close proximity with the tank wall by magnetic pads (13). An operator may enter and leave the canopy via an air lock (33), and a supply of clean air from a fan (23) is supplied to the interior of the canopy by an inlet duct (20) and maintained at a slight over pressure therein by a controlled air outlet duct (30). In the clean air zone created by the enclosure an operator on suspension lines (18) may carry out "hot work" on the tank wall while the supply of clean air is monitored, and the operation shut down automatically in the event of air contamination.

French Abstract

Enceinte de travail adaptée pour former une zone d'air propre au sein d'un environnement potentiellement dangereux tel qu'un réservoir de stockage de pétrole, l'enceinte comprenant une avancée (10) supportée par un cadre (11) et ayant une jupe (12) pour être maintenue à proximité étroite avec la paroi de réservoir par des semelles magnétiques (13). Un opérateur peut entrer dans cette avancée et la quitter via un sas (33), et une alimentation en air propre par un ventilateur (23) est assurée à l'intérieur de l'avancée par une conduite d'admission (20) et y est maintenue à une pression légèrement excessive par une conduite de refoulement d'air commandée (30). Dans la zone d'air propre créée par l'enceinte, un opérateur sur des lignes de suspension (18) peut réaliser un travail « à chaud » sur la paroi de réservoir tandis que l'alimentation en air propre est surveillée, et le fonctionnement automatiquement interrompu en cas de contamination de l'air.

Claims

10


CLAIMS


1. A working enclosure adapted to provide a clean air zone within a
potentially hazardous environment, the enclosure comprising a
canopy adapted to cover at least a part of a working surface to
define therewith a clean air zone, at least one air inlet duct
connecting said zone to a supply of clean air, means to monitor the
content of the air supplied to said zone, alarm/shut down
means responsive to the monitoring means, and means to discharge air
from the enclosure to establish a controlled operating air pressure within
the enclosure which is above ambient pressure outside of the canopy.

2. A working enclosure according to Claim 1, wherein the discharge
means is a duct having a diameter less than that of the clean air
inlet duct.

3. A working enclosure according to Claim 1, wherein the operating air
pressure within the enclosure is controlled within the range of 0.1 to
0.3 bar above ambient pressure outside of the canopy.

4. A working enclosure according to Claim 1, including an air lock in
the canopy wall to enable operator access without substantially
affecting the operating air pressure within the canopy.




11


5. A working enclosure according to Claim 1, including means to direct
air circulation around the interior of the canopy thus to ensure
substantially complete scavenging of any contaminant gases
therefrom.

6. A working enclosure according to Claim 1, wherein the canopy is in
the form of a flexible shroud supported by a frame and having a
peripheral skirt adapted to locate closely against the working
surface.

7. A working enclosure according to Claim 1, wherein the canopy has a
non-flammable internal surface.

8. A working enclosure according to Claim 1, wherein the canopy is
disposed upright, supported by rigging ropes.

9. A working enclosure according to Claim 1, wherein the air inlet duct
includes an open end to which is connected a fan supplying the air
through the duct into the enclosure, the duct being supported by a
frame at its open ends at a position remote from the canopy.




12


10. A working enclosure according to Claim 1, wherein the
alarm/shut down means is adapted to shut down the supply of
power to hot-work tools when used within the enclosure.

11. A working enclosure according to claim 1, wherein the canopy
is in the form of a rigid pre-shaped enclosure.

12. A working enclosure according to Claim 1, including a
plurality of magnetic pads attached peripherally to the canopy to
maintain it in close proximity with the working surface.

Description

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_ 1..
A WORKING ENCLOSTJRE
TI-11S INVF.NT1C)N concerns a working enclosure
adapted to provide a clean air zoy.Ze within a potentially hazardous
environment.
The inveni:ion is particularly though not exclusively
concerned with the provision of a clean air zone in the form of a
habitat within which sa-~~alted "hot work" may he carried out. t Iot
work may be deemed to ~~e any activity which has the potential to
introduce a source of ignition into a zone which may contain a gas
and air mixture within a flammable range. The lower limit of such
a range may be defined as the concentration below which there is
insufficient flammable g;as to support combustion and the upper
Limit may be the concentration above which there is insufficient air
to support combustion. Such work is often carried out in vessels
adapted to contain gas or flammable liquids such as the oil storage
tanks of crude oiI carriers. It is sometimes necessary, to carry
out, when such vessel;> are empty, repair work on parts of the
internal structure. This work nay involve welding or c:utdng, and
residues of gas and oil can cause an explosion when a source of

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ignition is intradueed into such a potentially hazardous
environment.
Patent specification No. G8 23I 1847 describes a
working enclosure adapted to provide a clean air zone within a
potentially hazardous environment, the enclosure comprising a
canopy adapted to cover at Ieast a part of a working surface to
define therewith a clean air zane, at least one inlet duct connecting
said zone to a supply afc~leun air, means to r~~onitor the content of
the air supplied to said zone, and alarm/ shut down means
responsive to the monit~~ring means.
The term "clean air" is to be construed as including
either fresh clean air which is free of acutely inflammable gases,
or for example., a mixture of clean air and an inert gas.
According to the present invention such a working
enclosure is improved by the provision of means to discharge air
from the enclosure to e;~tablish a controlled operating air pressure
within the enclosure.

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The discharge means may k~e a duct having a
diameter less than that e>f t:he clean air inlet duct.
The operating air pressure within the enclosure may
be controlled within the range of O.I to U.3 bar above ambient
pressure outside the canopy.
An air lock may be provided in the canopy wall to
enable operator access without substantially affecting the
operating air pressure within the canopy.
Means rr~ay be provided to direct air circulation
around the interior of the c.anapy thus to ensure substantially
complete scavenging of any contaminant gases therefrom.
The canopy may be provided :in the form of a flexible
shroud or a rigid enclo~,~ure or bubble.
Preferably,. the canopy also includes means whereby
the edges of the canopy nay be maintained in close relationship
with the working surface:.

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An embouiwent of the i.nvtsntion will now be
described, by way of example onl~.r, with reference to the
accompanying drawings in which:-
Fig. 1 is a perspective view of a working enclosure
as described in specification GB 23I1847 and
occupied bye an operator in readiness to carry out
work on a u~ertical surface within, far example, an
emptied c>il tank:
Fig. 2 i;~ a schernatie elevation of a working
enclosure: ~~nac~e in accordance with the invention
and locai:ed against a vertical wall;
and Fig. 3 is a schematic elevatiux~ of a rx~odified form of
enclosure when located against a horizontal
surface.
The cancyy IO made from, for example, a durable
material such as nylon ~ pre-treated or lined with a fire prevention
substance or blanket, is supported by a frame l I and has a

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_.
peripheral skirt 12 adapted to locate closely against a working
surface to which the device may be applied and retained by
magnetic pads 13. The canopy is supported from above by rigging
rapes 14 and 1 G. A sealable access flap 16 is provided through
which an operator 1? m:~y enter and leave the enclosure. One or
more suspension lines 'l 8 to support the operator, pass into the
canopy 10 through a generally sealed aperture 19 at the top of the
canopy. Thus the enclosure is located temporarily in a fixed
position against the working surface and in substantially sealed
engagement therewith try .means of the skirt I2, the flap 16 and
the aperture 1 ~.
An air° inlet duct 20 is connected to the canopy wall
and communicates witr~ tl~e interior of the enclosure. The duct is
preferably made from a flexible material and ,passes upwardly out
of the hazardous environment, for example, through an aperture
in a decking panel 21 and is supported above same by a frame 22
at the upper open end of which there is provided a fan 23
supplying air through t:he duct 20 into the enclosure. The fan 23
is associated with a sensing or monitoring device (not shown)

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which is further associated with a.n adjacent or remote alarm/ shut
down system for a purpose to be described.
Within an enclosure as described the operator may
carry out welding, cutting or similar operations without the risk of
causing an explosion since clean air is ducted into the enclosure
at a slight over-pressure thus bleeding from the flap I6 and
aperture 19, and around the skirt I2.
The upstanding frame 22 ensures that the fan
supplying clean air is disposed well above the deck 21 and any
low-lying gases which rnay be present.
1'he sensing or monitoring device associated with
the fan 23 is adapted to detect the presence of a toxic or
inflammable contaminant in the air being supplied to the
enclosure, and if present will either sound an alarm to alert the
operator or other staff thus to discontinue the hat work, or to shut
down the supply of power to whatever hot. work tools are being
used in the enclosure, or simply to shut down the fan supplying
the contaminated air tc~ the duct 20.

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When the vsrorking surface upon which the hot work
is being carried out is located between two potentially hazardous
zones, for example, when repairing a bulkhead separating two
hydro-carbon storage tanks, a second enclosure similar to that
described may be positioned on the opposite side of the bulkhead
whereat local heating of the working surface may otherwise create
an explosive condition. .
Referring now to Figs. :~ and 3 which schematically
illustrate an improverne:ot in accordance with. the present
invention, Fig. 'Z depicting the working enclosure located against
a vertical surface, and Fiy;. 3 depicting the enclosure against a
horizontal surface, therre is provided a discharge duct 30 in
communication with the: iruterior of the canopy at a position rermote
from that at which the air inlet duct 20 is connected. The
diameter of the discharl;e duct 30 is less than that of the inlet duct
20 thus to ensure a con trc:~lled over pressure within the canopy, of
between O.I and 0.3 b:~r above ambient pressure outside of the
canopy. If required, an adjustable constriction of pipe 30 may be
provided whereby the rata c3f discharge of air there through may be
selected.

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A bafflN 3 I within the canopy directa air circulation
axound the interior of the canopy as indicated by arrows ~2. This
ensures stabsta:ntially conr~.plete scavenging of any contaminant
gases therefrom.
Thus, by controlling the discharge of air from the
canopy as opposed to th<~ expedient of allowing it to bleed through
the aperture I9 as in Fig. I or around the skirt 12, maintains a
controlled amount of air over pressure within the canopy thus
avoiding discomfort for personnel within the enclosure or
insufficient pressured to ensure correct operation thereof.
An air fork 3~ is attached to the wall of the canopy
to enable operator access without substantially affecting the
operating air pressure ~uithxn the canopy.
Referring; raovv to Fig. 3 there is shown an alternative
configuration for the enclosure when located an a horizontal
working surface. In this example, the air infra and discharge
duds are connected to one end wall of the canopy while the access
air lock is located on tae opposite end wall.

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-S.)-
It is not inaended to limit the invention to the above
details. For example, the canopy 10 may be produced in the form
of a rigid pre-shaped en<:;lasure, and the air lock 33 may be
omitted in an application where the canopy is to be disposed over
a horizontal surface and lowered into place with an operator
already in position. Indeed, the form of the enclosure may differ
in many respects depending upon the application and location of
the work to be carried oat.

Representative Drawing