GB2291845A - Escape chute - Google Patents

Abstract

An escape chute assembly intended for use as a mass evacuation unit through which a succession of personnel can escape in an emergency from a multiple-occupancy work station (for example an offshore oil-drilling rig) comprising an elongate open-ended tunnel (e.g a succession of open-ended pipes linked together in use by harnesses, or a net tube) and a restraining means fitted inside or defined by the said open-ended tunnel and extending for some or all of the tunnel's length, the said restraining means being adapted such that the velocity of the descending escapee sliding down the inside of the chute is reduced to an extent that the escapee is less likely to suffer injury on emerging from the bottom of the chute. <IMAGE>

Description

IMPROVED ESCAPE CHUTE Field of the Invention The invention relates to escape chutes.

Background to the Invention The invention is particularly applicable to situations where there is a need for mass evacuation in an emergency from a multiple-occupancy work station such as an offshore oil-drilling rig. Recent well-publicised disasters in this area have highlighted the need, currently poorly fulfilled, to solve this problem. The convention life rafts do not solve it and their drawbacks have again been graphically illustrated by the television and press coverage of (for example) the "Piper Alpha" rig explosion and its aftermath.

One solution that has been developed to provide an emergency means of escape is provided in United Kingdom specification No GB 2 232 138. This invention provides for an escape chute assembly, intended for use as a mass evacuation unit through which a succession of workers can escape in an emergency from a multiple-occupancy work station (for example an offshore oil-drilling rig) and comprises a linked succession of open-ended pipes; each of which pipes is large enough internally for a worker to slide through; and all of which pipes are so linked as to define, in use, an elongate open-ended tunnel down which the escapees slide, and from which the escapees exit, under the force of gravity; the pipes being so shaped, sized and linked that in use they fit one within another to define a tunnel which has a substantially continuous interior, and at least some of the pipes articulate to allow the exit region of the tunnel to arc towards the horizontal.

When these escape chutes are intended for use on a water-surrounded work station they can incorporate at the bottom of the chute a pontoon, or a series of pontoons, into which the escapees automatically emerge.

Although these chutes are an improvement over the primitive means of escape previous employed, tests have shown that they suffer from at least one major disadvantage. Namely, the terminal velocity of the escapee may be so great under certain circumstances that he/she can sustain injury on emerging from the end of the chute into the pontoon or water.

The velocity reached by the escapee depends upon a number of factors including the weight of the escapee and the degree of friction between the escapee's outer clothing and the body of the chute.

This latter factor can be an extremely complex one. Workers on an offshore oil-drilling rig will usually wear special protective clothing and there are many types of this clothing in use around the world. It has been observed in trials that some types of clothing create very little friction as the escapee descends the tube and as a result they emerge onto the pontoon at considerable speed and certainly fast enough to cause personal injury.

This situation is further compounded if the inside of the tube is wet. This is quite a likely occurrence at sea where rain, swell or fire-fighting water can easily enter between the succession of linked, open-ended pipes.

It is the object of this invention to produce an escape chute which overcomes these disadvantages.

Summarv of the Invention In its broadest sense, the invention provides an escape chute assembly, intended for use as a mass evacuation unit through which a succession of personnel can escape in an emergency from a multiple-occupancy work station (for example an offshore oil-drilling rig) comprising an elongate open-ended tunnel (eg. a succession of open-ended pipes linked together in use by harnesses, or a net tube) and a restraining means fitted inside or defined by the said open-ended tunnel and extending for some or all of the tunnel's length, the said restraining means being adapted such that the velocity of the descending escapee sliding down the inside of the chute is reduced to an extent that the escapee is less likely to suffer injury on emerging from the bottom of the chute, the restraining means preferably comprising a knitted tube or sock.

The knitted construction provides a degree of elasticity which allows the evacuee to control his rate of descent More preferably the restraining means comprises a KERMAL (Trade Mark) elasticated seamless knitted tube. Spun KERMAL has non-flammable elastic properties which it has been discovered, make it well-suited to this particular application.

Advantageously the restraining means comprise portions of the harness which are adapted in use to run down the inside surface of some or all of the open-ended pipes.

Brief Description of the Drawings The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 shows a diagrammatic representation of a restraining tube at the access end of an emergency escape chute; Figures 2 and 3 show a side elevation of a restraining tube suspended within a netting tunnel supported on a pontoon at high and low water respectively.

Figure 4 illustrates diagrammatically how an evacuee exits an escape chute as illustrated in Figures 2 and 3 at various water levels; Figure 5 shows various stages of the descent of an evacuee down an escape chute according to the present invention; Figure 6 shows configurations adopted by the pontoon in a variety of tidal conditions.

Description of the Preferred Embodiments The present embodiments represent currently the best ways known to the applicant of putting the invention into practice. But they are not the only ways in which this could be achieved. They are illustrated, and they will now be described, by way of example only.

This specification should be read in conjunction with GB 94 05117.4 and for the avoidance of doubt we hereby import the text, drawings and text contained within the drawings from GB 94 05117.4 into this specification.

Chute assemblies according to the present invention are typically intended to be mounted on an access support platform on a multiple-occupancy work station, for example an off-shore oil-drilling rig. However, it will be appreciated that this invention is equally applicable to any situation where personnel need an emergency escape route to a lower level.

Figure 1 illustrates a series of open-ended pipes of generally frusto-conical shape being so sized, shaped and linked together that they fit one within another to define a tunnel which has a substantially continuous interior. The pipes can be telescoped one within another when not in use although they are illustrated in an extended configuration.

Extending down the inside of the pipes is a restraining tube 10 which in this example is a knitted elasticated sock. In the subsequent description for simplicity, a male escapee will be described but this terminology should be taken to cover both male and female personnel. An escapee entering the top of the escape chute is automatically directed into the restraining tube 10 by an inner sleeve 11 which is attached to the outer rim of the uppermost pipe.

The inner sleeve in this example is made of canvas but any strong durable material will suffice.

Optionally, the restraining tube 10 is attached to the inner sleeve 11 by a shock-absorbing section 12. This section also has the effect of reducing the diameter from that of the access point to that of the restraining tube itself.

This is important for psychological reasons and to allow for immediate contact with the restraining tube upon entry into the system.

The restraining tube is made of KERMAL (TM), in this example, which stretches width-ways and elongates, permitting the passage of evacuees of all shapes and sizes, and because of the downward force exerted on the tube by the first evacuee, a second, following evacuee cannot descend. Thus a selfregulating effect is achieved.

During proving trials on a TELESCAPE (TM) prototype system (PCT/GB90/00525) it became apparent to the designers that slow-down techniques were required within the chute particularly in wet conditions. One of the devices introduced for this purpose was a woven tubular fabric made of KERMAL through which an evacuee could descend within the protection of the glass reinforced plastic cone chute. This corresponds to the arrangement described in Figure 1.

In the meantime, it had become clear that the industry was no longer in favour of relatively expensive evacuation systems which created their own maintenance work load. The trend towards a construction of normally unmanned installations and the de-manning policy drew the inventors to design a maintenance-free, dry evacuation system, utilising the restraining tube as its means of controlled descent onto a landing platform or pontoon.

Nearly 500 descents have now been made down the same 20 meter tube by personnel of all sizes, attired in a variety of footwear and clothing, including survival suits and life jackets. There has thus been developed a fair-weather system based on the restraining tube for normally un-manned installations, whilst keeping the TELESCAPE system available for all-weather situations.

It should be understood that working visits to un-manned installations would be infrequent and only made in fair-weather conditions.

It was quickly appreciated that the landing platform (pontoon) stationholding capabilities would be one of the hardest areas to design. Contact between the pontoon and the installation legs would have to be prevented.

The restraining tube is effective only if unconstrained, except for securing it at the entry level. Therefore a separate connection would be required between the structure and pontoon to hold the pontoon on station. It was discovered that descent through the restraining tube could be made with the tube at an angle. Therefore "on-station" would mean restraining the pontoon from impact with the legs, and within an excursion zone which would allow safe descents to be made. Thus a second connection between the structure and the pontoon has to be devised to guide the restraining tube into a central point on the pontoon when off-vertical.

A tarpaulin entry funnel was inefficient and cumbersome, so that redesign was necessary. Eventually the restraining tube began to ladder at the stitching points between tarpaulin and KERMAL, leading to a re-think of the entire entry point. Some difficulty had been experienced in entering the restraining tube via the tarpaulin funnel. It was deemed necessary to reduce the size of the entry cone for psychological reasons and to allow for immediate contact with the restraining tube upon entry into the system. The combination of a canvas funnel in the form of a tapered sleeve followed by a seamless nylon shock-absorbing section was found to be most effective.

Initial preference for the pontoon to be a standard covered life raft was considered unworkable due to difficulty of entry. An open thirty man raft would suffice, but it was decided to proceed with a larger raft to provide a safe and secure landing area of greatest stability in rough conditions. Most importantly would be the need to cope with sea conditions affected by tide, tidal stream, wave and wind. Vertical flexibility in system deployment lines would be essential to the development of an effective system.

The key to a successful system is in compensation devices without constraint upon the restraining tube. A flexible connection has to be maintained between the structure and the pontoon whilst the restraining tube remains free to deliver evacuees into the pontoon. It was assumed that the higher the operational capability the more successful the system would be on the market. However, raising the upper operational limits poses greater problems in station-holding. A balance has to be established between system operation at high and low water levels, including wave variations, and limits installed to prevent undue pontoon excursion. It has thus been possible to develop a "carry-on" system which appeals to the industry, a system which could be positioned and operated without mechanical aids or rig power, and with a minimum of installation engineering.

Modelling techniques were used to determine deployment line configuration and spread points at structure level. Elasticity was introduced into the lines connected at different points on the model pontoon to act as water level compensators. Both configuration and elasticity were variously tried for pontoon station-holding methods. Under extreme force on the pontoon, representing very strong tidal currents, it appeared that the pontoon could be moved so far off station so as to jeopardise easy and safe descent. Trials were carried out on a full size descent restraining tube with shock cords, which were to be tried as the flexible link in the system, to establish the relationship between force and stretch.In order to guide the full size sock into the pontoon a 17 metre length of plastic tube of 1.3 meter diameter was made up and attached to the pontoon by shock cords and secured to the entry pod at the 30 meter level on a tower. A bogey device was constructed to which the pontoon was secured so that excursion could be measured and descent through the restraining tube made to ascertain maximum operational pontoon excursion.

Tests were conducted on shock cords to find the stretch of cord which would allow the pontoon to ride through various water levels. The known weight of the pontoon in its valise, and independent of it, was related to the stretchability of a 12.5 millimetre shock cord to establish the overall length of the cord to be used. This stretch had to be equal to that of the combined tidal range and low water trough distance in mid-range beaufort conditions. This distance was then applied to the possible excursion of the pontoon in tidal streams of 3 to 5 knots. It was decided to restrict the excursion to the distance referred to by way of halter lines. Halter lines would run parallel to the shock cords, longer than the latter by the amount calculated to cope with the vertical rise and fall of the sea (see figures 2 and 3).

The weight and station holding properties of the pontoon are clearly important factors. A RFD 65 FERRYMAN was used in a further series of trials involving an adjustment in the length of shock cords to compensate for the lighter weight of this type of pontoon. The reason for this being that the shock cord extended relatively easily over the short term with resistance increasing with a degree of stretch. In this case force provides resistance, the less force the longer a shock cord required to provide the compensation required. It was found that the shock cords under examination would stretch 50% under the load applied to them; equal to that of the mass of a 65 FERRYMAN. Further resistance would occur once the sea pockets of the pontoon filled. It was decided that the stretch of 50% had to equal that of the difference between high and low water plus a significant wave trough.Thus the overall length deployment means could be calculated, i.e shock cord plus fixed line to equal the distance between the structure attachment point to pontoon sponson. To obtain excursion distance one had to add the length of fixed line to the halter line and then prescribe an arc from structure attachment point to pontoon sponson using the measured distance as a diameter. This is illustrated in more detail in Figure 6.

To overcome concerns that strong winds would blow the plastic tube off line a design change was made to co-polymer netting. This was sewn into a tube, the lower end flared to present ease of exit from the restraining tube and connected to the pontoon by small lengths of shock cord. This netting, known as "the sleeve" offered much less resistance to the wind. It also provided some additional anti-excursion control. This type of arrangement is shown more clearly in Figures 2 and 3.

In order to easily disconnect the pontoon from its lines, it was decided to attach all shock cords and the halter lines to a few quick release couplings secured to the pontoon. The pontoon would have to be released from its lines following system deployment and use for repacking purposes. In an emergency, and providing that the tidal stream would favour such an action, the pontoon would be quickly released to float away with its evacuees.

Another quality of the netting sleeve was its capacity to elongate by at least 15% under load, a factor which proved to be invaluable in compensation.

That, coupled with the shock cord connections to the pontoon, allowed the restraining tube to be guided centrally when the pontoon was forced off station During trials the longitudinal stretch of the sock was recorded at 15% under average body weight and size. In order for an evacuee to exit the sock cleanly, that is to gain a foothold on the pontoon whilst the body is still within the sock, the length of the sock was calculated at air gap minus 15%. This would mean that at low water a drop of 2 to 3 meters into the soft pontoon floor would occur (see Figures 4 and 5). However the restraining tube produces a complexity of stretch factors, depending upon the actions of an individual evacuee.For instance, should a slightly built person descend passively, without creating any resistance by use of the arms and legs, descent will be quick and the restraining tube will stretch less than 10%, whereas a heavily built person would fill the sock width ways causing more elongation of the restraining tube. Should the slightly built person spread arms and legs in the prescribed "star" fashion descent will be slowed and restraining tube elongation occur. Maximum restraining tube stretch is about 30% but this is unlikely to be achieved by human beings.

At training sessions it would be made clear that the "star" descent method is the most sensible and safe to use culminating in a soft landing. Following observations of hundreds of descents by persons of all shapes, sizes and weights, wearing a variety of apparel, it was noticed that a free fall through the first half of the sock followed by maximum resistance in the lower half achieved the longest stretch. When this method is used exit from the restraining tube is very slow, and therefore landing is made as safe as possible. Training will focus on strict adherence to the safest method of descent.

Systems of this type have performed well in wind, wave and a strong current which were co-linear, a combination which provided a stern test for the system. This system has therefore been validated in beaufort conditions which would be expected during visits to not normally manned installations.

It will be appreciated that weights can be employed which attach directly or indirectly to the pontoon or link to the pontoon via buoys (not illustrated).

These can be added to the system in order to increase the stability of the pontoon itself. Some of the deployment lines can be discarded in this case.

In certain circumstances, for example land-base use, the outer tunnel, which comprises the frusto-conical shaped pipes, or the netting tube can be dispensed with. Thus a single-layer restraining tube, made for example from KERMAL, can be used as a means of escape. However, its mounting onto the access point is clearly a key and integral feature of this invention the heavy duty nylon seamless section acting as a shock absorber between the canvas entry sleeve and the restraining tube itself.

As an alternative to the sock or tube restraining means, the harnesses which join together the series of open-ended pipes can themselves be used as a restraining means. These harnesses are commonly made of KEVLAR (TM) and routing them inside the pipes (not illustrated) and providing them in sufficient number has been found to create sufficient friction between the escapee and the inside of the tunnel to act as a restraining means.

Summarv of Svstem Benefits (i) Simple system operation (deployment can be achieved in one minute).

(ii) Dry protected descent, averaging 10 second per person.

(iii) A stable landing area is provided.

(iv) Maintenance-free operation.

(v) Corrosion-proof, non-flammable components which provide protection from flame and radiant heat.

(vi) Lightweight, less than 400 kilos in total.

(vii) Sectionalised for easy transportation and installation.

(viii) Easy change-out of pontoon valise.

(ix) Quick release couplings between pontoon and escape chute.

(x) Stretcher handling capability is provided within a protected area.

Claims (5)

CLAIMS:

1. An escape chute assembly intended for use as a mass evacuation unit through which a succession of personnel can escape in an emergency from a multiple-occupancy work station (for example an offshore oil-drilling rig) comprising an elongate open-ended tunnel (e.g a succession of open-ended pipes linked together in use by harnesses, or a net tube) and a restraining means fitted inside or defined by the said open-ended tunnel and extending for some or all of the tunnel's length, the said restraining means being adapted such that the velocity of the descending escapee sliding down the inside of the chute is reduced to an extent that the escapee is less likely to suffer injury on emerging from the bottom of the chute.

2. An escape chute assembly as claimed in Claim 1 wherein the restraining means comprises a knitted tube or sock, mounted substantially coaxially inside the open-ended tunnel.

3. An escape chute assembly as claimed in Claim 1 or Claim 2 wherein the restraining means comprises a KERMAL (Trade Mark) elasticated seamless knitted tube.

4. An escape chute assembly as claimed in Claim 1 wherein the restraining means comprises portions of the harness which are adapted in use to run down the inside surface of some or all of the open-ended pipes.

5. An escape chute assembly substantially as herein described with reference to and as illustrated in any combination of the accompanying drawings.