GB2302902A - Fire resistant glazing assembly - Google Patents

Abstract

A fire resistant glazing assembly has glass supported 4 in a glazing pocket 7 of a frame 5, 6. The edge of the glass in the glazing pocket is fitted with a metallic channel-shaped edge member 10, bonded to the glass by means of a high temperature thermally conductive refractory adhesive 11 and movably retained in the glazing pocket by a fire resistant glazing tape 12, for example of soft ceramic fibres. The edge member increases the conduction of heat into the edge of the glass and reduces the likelihood of thermal shock and also reduces the edge cover of the glass and therefore the field of thermal shock. A suspension system 14 is designed to accommodate limited relative movement of the glass and frame owing to the difference in thermal conductivities and to prevent the glass from leaving the glazing pocket as it sags in the plastic phase at high temperatures. The invention can be used in smoke containment systems.

Description

FIRE RESISTANT GLAZING The present invention relates to fire resistant glazing.

Fire resistant glazing uses a beaded framework to retain thermally toughened glass which is a recognised medium for fire resistance. The framework, which may be constructed from steel, timber, or other fire resistant materials often incorporates fixing arrangements to support doors or windows.

Such glazing must meet several safety design criteria in order to be effective. Such criteria are often defined in national or international performance standards such as British Standards in the United Kingdom.

First, it is necessary for the glass to withstand rapid increases in temperature which occur particularly in the early stages of a fire. For example, in a test described in British Standard 476 parts 20-23 the glass should withstand an initial temperature rise of 5000C in approximately three minutes. This results in a significant temperature differential being established between the main body of the glass and its edges which are retained by the framework in what is known as a "glazing pocket." Such a temperature differential can be well in excess of 250 C and creates a tendency for the glass to fracture or shatter as a result of thermal shock The greater the depth of the glazing pocket and hence the amount of glass edge covered the more critical thermal shock becomes.

Secondly, it is desirable for the edge of the glass to be covered by the frame by an adequate amount to reduce the risk of the glass springing out of or otherwise leaving the frame when under impact, load or when subjected to high temperature. This is particularly important when the glass is to be used in a protective barrier in and about buildings. For example British Standard 6180 specifies that 15mm of the glass edge should be covered. This is also a requirement of CP3 Chapter IV in relation to loadings applied by wind pressure.

It will be understood that the first criteria is in direct conflict with the second. Increased edge cover of the glass to prevent it leaving the framework results in an increased likelihood of failure from thermal shock.

A third requirement is for the glass to meet integrity standards. During a fire the temperature of glass may exceed 7200C which is the point where glass starts to become plastic and will sag under its own weight. The glass tends to pull away from the glazing pocket at the top and sides of the frame resulting in an integrity failure. One example of an integrity standard is British Standard 476 parts 20-23.

Fourthly, it is important to allow relative movement of the glass and framework when the glazing is subject to heat. The expansion coefficients of glass and frames of, for example, steel or wood are greatly different and the different rates of expansion must be accommodated. This conflicts with the need for the glass edge to be fixed to counteract the sagging problem described in the above paragraph.

In addition to the above four requirements the glass must be thermally toughened so that it meets the impact requirements for a safety glass such as those specified in British Standard 6206.

It is an object of the present invention to obviate or mitigate the aforesaid disadvantages and to meet the safety design criteria specified above.

According to the present invention there is provided a fire resistant glazing assembly comprising a frame in which a glass pane is received, at least one edge of the glass received by the frame being covered by an edge cover member having a greater thermal conductivity than that of the glass.

Preferably the edge cover member is in the form of a metallic channelshaped member which fits over said edge of the glass. The channel-shaped member is preferably manufactured from steel.

The edge cover member is preferably fixed to the edge of the glass by means of a high temperature thermally conductive refractory adhesive.

The edge cover member is conveniently received in the frame so that it is moveable relative thereto between first and second positions. This permits relative movement of the glass into the frame up to a first position and out of the frame up to a second position.

Preferably a suspension member is fixed to the edge cover member and is moveable therewith relative to the frame between said first and second positions.

The suspension member may be moveable relative to a stop member of the frame in such a way that movement of the edge cover member and suspension member is limited by abutment with the stop member in said first and second positions.

There may be a clearance between the edge cover member and the suspension member, the clearance receiving the stop member. Alternatively the suspension member may have an elongate slot which is moveable over the stop member.

Alternatively the suspension member is located in an aperture in the frame, a portion of which around the aperture acts as the stop member, wherein the suspension member has at least one enlarged portion greater than the size of the aperture, the enlarged portion abutting the stop member in said first or second position.

In an alternative embodiment there is provided a beading which is fixed to the frame and captively retains the edge cover member so that it is moveable therein.

Specific embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a typical front view of glass panes retained in frames using a glazing assembly of the present invention; Figure 2 is a sectioned view of a glazing assembly along line BB of figure 3 according to a first embodiment the present invention; Figure 3 is a sectioned view along line AA of figure 2; Figure 4 is a sectioned view along line AA of figure 5 of a second embodiment of the present invention; Figure 5 is a sectioned view along line BB of figure 4; Figure 6 is a sectioned view of a third embodiment of the present invention; Figure 7 is a sectioned view along line AA of figure 6; Figure 8 is a sectioned view of a fourth embodiment of the present invention; Figure 9 is a sectioned view along line AA of figure 8;; Figure 10 is a sectioned view along line BB of figure 8; Figure 11 is a sectioned view of a fifth embodiment of the present invention; Figure 12 is a sectioned view along line AA of figure 11; Figure 13 is a sectioned view of a sixth embodiment of the present invention; Figure 14 is a sectioned view along line AA of figure 13; Figure 15 is a sectioned view along line BB of figure 13; Figure 16 is a sectioned view of a seventh embodiment of the present invention; Figure 17 is a sectioned view of a eighth embodiment of the present invention along line AA of figure 19; Figure 18 is a sectioned view along line BB of figure 17; Figure 19 is a sectioned view of an ninth embodiment of the present invention; Figure 20 is a sectioned view of a base edge of a glazing assembly in accordance with the present invention; ; Figure 21 is a sectioned view of a door and frame having a glazing assembly in accordance with the present invention; Figure 22 is a sectioned view of a mid-frame having a glazing assembly in accordance with the present invention; Figure 23 is a sectioned view of a smoke screen suspended using a glazing assembly in accordance with the present invention; Figure 24 is a view on arrows AA with fixings removed for clarity; Figure 25 shows three graphs illustrating schematically how glass size can be selected for a particular application.; Figure 26 is a front view of a tenth embodiment of the present invention; Figure 27 is a sectioned view along line AA of Figure 26; Figure 28 is a sectioned view along line BB of Figure 26.

Referring now to the drawings, figure 1 shows a typical arrangement of glass windows 1 and doors 2 to which the present invention has application. The panes of glass 1,2 are supported in a framework 3 and it will be seen than one framework member may support two panes of glass. The dotted lines show how the framework may be continued.

Figures 2 and 3 show a first embodiment of a glazing assembly in which a pane of glass 4 is supported between two frame members 5,6 . A first frame member comprises a steel box section 5 and this is connected to a second channel-shaped pressure plate 6 on the other side of the glass 4. The frame members 5,6 are spaced apart to define a glazing pocket 7 by means of a channel-shaped stop plates 8, which are spaced at intervals along the frame, and a continuous top transom 9.

The edge of the glass 4 is covered by a steel channel-shaped edge member 10 which is bonded thereto by means of a high temperature thermally conductive refractory adhesive 11. The edge member 10 is movably retained between the frame members 5,6 by means of a fire resistant glazing tape 12 manufactured from, for example, soft ceramic fibre. The tape 12 adheres to the frame members 5,6 and resiliently supports the edge member 10 on each side. Above the edge member 10 there is welded a discontinuous channel member 13 effectively extending the depth of the glass edge received in the glazing pocket 7. Each space between adjacent lengths of the discontinuous channel member 13 accommodates a stop plate 8 and a stepped suspension bracket 14 welded to the surface of the edge member 10.A free limb 15 of the stop plate 8 is received in a clearance 16 defined between the bracket 14 and the edge member 10.

The glazing assembly is held together by means of a bolt (not shown but indicated by a centre line in figure 2) which passes through apertures (not shown) in the frame members 5,6. The aperture in the box section frame member 5 is threaded. This particular glazing assembly is used on top or side frames.

In use, the glazing assembly allows for limited movement of the glass 4 and edge member 10 relative to the glazing pocket 7. The glass 4 is supported in the glazing pocket 7 by the stop plate 8 engaging under the stepped suspension bracket 14 to which the edge member 10 is fixed. If during a fire the glass 4 reaches the plastic phase temperature its tendency to slump will be prevented by the stop plate member 8 engaging with the stepped suspension bracket 14. If the glass 4 should move relatively inward of the glazing pocket 7 its travel is limited by the top surface of the edge member 10 abutting the free limb 15 stop plate 8.

It will be understood that the movement of the glass 4 within the glazing pocket 7 is limited by the clearance 16 between the suspension bracket 14 and the edge member 10.

The provision of the edge member 10 has a four-fold effect. First, the edge member 10 increases the conduction of heat into the edge of the glass 4 which is not exposed directly to the fire as it is covered in the glazing pocket 7. This increase in conductivity reduces the likelihood of thermal shock and consequent failure of the glass. Secondly, the provision of the edge member 10 reduces the edge cover of the glass 4 and therefore the field of thermal shock. Thirdly, the overall edge cover of the glass 4 within a glazing assembly is not compromised and the tendency of the glass 4 to leave the frame during load, fire or impact is not decreased. Finally, the edge member 10 allows the glazing assembly to have a suspension system as described above and to accommodate limited relative movement of the glass and frame owing to their different thermal conductivities.

At high temperatures the glass may enter the plastic phase and sag or slump under its own weight. In these circumstances, there is a tendency for the glass 4 to pull away from the glazing pocket 7 at the top and side of the frame. The suspension system is designed to prevent the glass 4 from leaving the glazing pocket 7.

Figures 4 to 24 show alternative glazing assemblies that may be used whilst still employing the steel edge member 10. Features which are common between the drawings are represented by the same references but increased by a factor of 100 and will not be described in detail again. The embodiments described below have the advantages described in the preceding paragraph as a result of using a steel edge member.

A second embodiment of a glazing assembly shown in figures 4 and 5 has an alternative suspension member 117 located in intervals between adjacent discontinuous channel members 113. The suspension member 117 is a substantially L-shaped bracket and is welded to a top surface of the edge member 110. An upstanding limb 118 of the bracket has an elongate slot 119 which fits over a self-tapping screw (not shown but indicated by centre line 120) fixed to the box section frame member 105. Limited movement of the frame and glass is accommodated by the movement of the bracket 117 over the screw between the extremes of the slot 119.

Figures 6 and 7 show a frame that comprises major and minor box sections 221, 222. The major box section 221 has a skirt 223 depending from one corner. The minor box section 222 is fixed below the major box section 221 adjacent to, but spaced from, the skirt 223. The glazing pocket 207 is thus defined between the skirt 223 and a facing wall 224 of the minor box section 222.

The surfaces of the skirt 223 and minor box section 222 that face internally of the glazing pocket 207 are lined with a ceramic glazing tape 212 as described in the previous embodiment. The pocket 207 receives the glass 204 fitted with the edge member 210 and the discontinuous channel-shaped member 213 described above. In the intervals between adjacent discontinuous channel-shaped members 213 the glass 204 and edge member 210 are captively retained in a beading 225 in the form of a longitudinally slotted box section having rear and side walls 226, 227 and a slotted front wall 228 . The beading 225 is fixed to the major box section 221 of the frame and receives glass 204 through the slot in the front wall 228.The glass 204 is suspended in the frame whilst permitting movement of the glass relative thereto by virtue of a clearance 229 between the edge member 210 and the rear wall 226 of the beading 225. Movement of the glass 204 out of the glazing pocket 207 is prevented by the edge member 210 on the glass 204 abutting the front wall 228 of the beading 225.

Figures 8, 9 and 10 show a glazing pocket 307 defined by major and minor box sections 321,322 as described in relation to figures 6 and 7 above. The wall of the major box section 321 adjacent the glazing pocket 307 has an aperture 330 in the form of a circular bore 331 with a radially extending slot 332 (see figure 10). The aperture 330 is designed to receive a bolt shaped suspension member 333 one of which is attached to the edge member 310 at each interval between adjacent discontinuous channel shaped members 313. The suspension member 333 has a cylindrical head 334 of a diameter that will just pass through the circular bore 331 of the aperture 330, and a shank 335 that will pass through the slot 332 of the aperture 330.When assembling the glazing the suspension member 333 is inserted through the circular bore 331 of the aperture 330 and is then moved along the slot 332 so that it is retained by virtue of the head 334 not being able to pass there through. When the minor box section 322 is fixed in place the suspension member 333 is prevented from moving back to the circular bore 331.

In this embodiment movement of the glass 304 out of the glazing pocket 307 is prevented by the suspension member 333 being retained in the slot 332 as the head 334 abuts the area around the slot 332. Limited relative movement of the glass 304 into the glazing pocket 307 is accommodated by the suspension member 333 and glass 304 being able to move upwards relative to the slot 332 to a point where the discontinuous channel members 313 abuts the major box section 321.

Figures 11 and 12 show the same frame arrangement as discussed in relation to figures 6 and 7 above. In this embodiment the stop plate 436 is an L shaped plate a main limb 437 of which projects into space 438 in the glazing pocket 407 above the edge member 410 and at a predetermined clearance from a lower wall 439 of the major box section 421. The stop plate 436 co-operatively engages with a C-shaped suspension member 440 fixed to the edge member 410.

A free limb 441 of the suspension member 440 extends into the clearance 438 so that it is able to move between the lower wall 439 of the major box section 421 and the main limb 437 of the stop plate 436. The clearance 438 allows movement of the glass 404 and edge member 410 relative to the glazing pocket 407.

Figures 13, 14 and 15 show a glazing assembly which is similar to that shown in figures 8, 9 and 10. In this embodiment the glass 504 is suspended by an H-shaped suspension member 542 which is captively retained in a narrow part 543 of a T-shaped aperture 544 (see figure 15) in the lower wall 539 of the major box section 521 adjacent the glazing pocket 507. The suspension member 542 is retained as a limb 545 of the H is greater in size than the narrow part 543 of the aperture 544. The other limb 546 of the suspension member 542 is fixed to the edge member 510 on the glass 504.The suspension member 542 permits limited movement of the glass 504 relative the glazing pocket 507 between the position where the limb 545 retained in the major box section 521 abuts the lower wall 539 around the aperture 544 and the position where the discontinuous channelshaped members 513 abut the major box section 521.

Figure 16 shows an alternative frame assembly with a glass suspension arrangement of a kind already described. This embodiment is used for insulated frames and comprises two rectangular box sections 650 separated by a block of insulating material 651. One of the rectangular box sections has a depending skirt 652. The glazing pocket 607 is defined between the skirt 652 and a third box section 653 fixed below the rectangular box section 650 without a skirt. It will be seen that thicker glass 604 is used for insulating applications.

Figures 17 and 18 show a mid-rail frame 755 with glass 704 above and below the frame. The glass 704 fitted below the frame is glazed with a suspension arrangement described in relation to the embodiment shown in figures 2 to 4, whereas the glass above the frame does not require suspending as it will be supported from below by the mid-rail frame and accordingly is simply fitted with an edge member 710 and supported between glazing tape 712.

Figure 19 shows how the glazing assembly may be used in relation to wooden frames. The embodiment shown is a mid-rail frame 855 having glass 804 above and below. Again, it will be understood that the glass above the frame does not require a suspension arrangement. The inclined centre lines 856 represent screw fixings to connect the separate elements of the frame.

Figure 20 shows a base frame 960 supporting glass 904 in a glazing pocket 907 between a box section 905 and a pressure plate 906. As the base frame supports the glass from below a suspension arrangement is not required.

Figure 21 shows how the glazing may be applied to a door 1061 and door frame 1062. A clearance 1063 between the door 1061 and frame 1062 is closed by a brush seal 1065. The door 1062 is recessed to accommodate an intumescent seal 1066. Both the door 1061 and the frame 1062 have glazing pockets 1007 in which glass 1004 fitted with an edge member 1010 is received. Each pocket 1007 has glazing tape 1012 and a clearance 1067 to permit movement of the glass relative to the pocket 1007 Figure 22 shows another mid-rail frame 1155 in which the lower glass 1104 has a suspension arrangement of a kind already described in relation to an earlier embodiment. It will be appreciated that any suitable suspension arrangement may be used. In this embodiment the frame comprises a central Tshaped member 1170 filled on each side by a box section 1171 to form two opposed glazing pockets 1107.

Figures 23 and 24 show a glazing assembly used in relation to smoke screens which are typically suspended from the ceiling of a building or from any convenient structure above a ceiling so that the glass projects downwardly through the ceiling and contains the spread of smoke.

The glass 1204 is fitted with an edge member 1210 by the high temperature adhesive 1211 and is sandwiched between spaced metallic plates 1280. The plates 1280 are suspended from a T-shaped bracket 1281 by a bolt 1282. The bracket 1281 is itself bolted to the ceiling or to any convenient structure above the ceiling so that the glass 1204 depends through the ceiling.

Several such bracket 1281 and plate 1280 fixing arrangements may be spaced along a single length of glass 1204.

In between the plates 1280 and the glass 1204 is a ceramic glazing tape 1212 as described above.

A bolt 1283 passes through apertures in the glass 1204 and the plates 1280 and has concentric ferrules 1284, 1285 fitted between external washers 1286. An outer ferrule 1284 is made of nylon or the like whereas the inner ferrule 1285 is steel.

The glazing pocket 1207 is thus defined in the region between the plates 1280 and a stem 1287 the T-shaped bracket 1281. A clearance 1288 between the edge member 1210 on the glass 1204 and the bracket 1281 permits relative movement of the glass 1204 and the glazing pocket 1207.

When the smoke screen is subjected to high temperatures the nylon ferrule 1284 begins to melt and the glass 1204 may move down the glazing pocket 1207 through the melted nylon until it abuts the metal ferrule 1285. In an extreme condition, if the temperature reaches such a value that the glass 1204 starts to slump it may pass over the metal ferrule 1285 but will be prevented from leaving the glazing pocket 1207 by virtue of the edge member 1210 coming in to contact with the metal ferrule 1285.

Figure 25 shows three graphs a) to c) illustrating schematically how the present invention allows the size of glass to be selected for a particular application with more precision than has hereto been possible.

Graph a) shows that the strength of the glass decreases as the temperature increases. At t3, F3 the glass becomes soft and failure commences.

Graph b) shows a plot of temperature against time. It will be seen that the British Standard requirement is for the glass to withstand a rapid increase in temperature in the first 30 minutes. The actual temperature is measured with a thermocouple placed on an unexposed face of the glass (i.e. on the opposite side to the fire) and consequently the temperatures tl to t3 will be less than that of the fire as the unexposed face will be cooler.

If a 3m2 piece of glass had reached point t3, F3 after a 90 minutes test then this information can be extrapolated to ascertain what size of glass could be used if it was only required to withstand 60 mins or 30 mins of the BS test. The extrapolation is shown in graph c) and it will be understood that a larger size of glass could be used to withstand shorter time periods. This is all made possible by the present invention which prevents the glass from slumping and provides support to maintain the glass integrity for a larger period of time than has heretofore been possible. Thus the invention permits an easy method of selecting maximum glass size in relation to the performance time required.

Figure 26 shows a front view of an alternative glazing assembly in which fire resistant glass 1201 is supported in a framework of transparent ceramic glass 1203.

In Figure 27 it is shown that two adjacent panes of glass 1204 are supported on opposite sides by ceramic glass cover plates 1203. Thus the edge of each glass pane 1201 is received in a pocket 1207 defined between the glass cover plates 1203. A silicone seal 1286 is provided in a clearance between the adjacent ends of the glass panes 1207.

The ceramic glass cover plates 1203 are fixed to the glass edges by means of stainless steel bolts 1287 spaced along the length of the glass. Each bolt 1287 is received in a stainless steel sleeve 1288 that has an integral radial flange 1289 at an end opposite the opening for the bolt. The head of the bolt is received in a countersunk stainless steel cap 1290 that matches the flange 1289 on the opposite ceramic glass cover plate 1203. Apertures in the glass pane 1204 and in each of the ceramic glass cover plates 1203 are lined with a nylon ferrule 1291 that receives the steel sleeve 1288. Neoprene washers 1292 are placed between the cap 1290 and ceramic glass cover plate 1203 and, on the opposite glass face, between the flange 1289 and the ceramic glass cover plate 1203. A clear flexible gasket 1293 is provided between the glass pane 1204 and the cover plate 1203.

A similar arrangement is shown in figure 28 in which ceramic cover plates 1203 are used to line the edge of a glass pane 1204 that has no immediate neighbour pane. The cover plates 1203 are fixed to the glass pane 1204 using the same fixing arrangement as described in relation to figure 27. The exposed ends of the glass pane 1204 and ceramic glass cover plates 1203 are covered by a stainless steel channel member 1294.

The ceramic glass cover plates 1203 each have a thermal conductivity greater than that of the glass panes 1204 and the assembly therefore has the same advantageous properties as discussed in relation to the earlier embodiments. The cover plates provide stability to the glass panes as they enter the plastic phase and start to slump during heating. The radiated heat permeates through to the glass edge and the likelihood of thermal shock is thereby reduced.

The assembly allows for limited relative movement of the glass panes 1204 by virtue of the nylon ferrules 1291 between the glass panes 1204 and the fixings.

The nylon softens during heating and permits movement of the glass in the early stages, whilst supporting it in the later plastic phase. This extends the integrity performance of the glazing assembly.

The added advantage of having a ceramic glass cover plate is that the glazing assembly is aesthetically pleasing in architectural terms since visually it appears to be a frameless glazing assembly.

Claims (20)

1. A fire resistant glazing assembly comprising a frame in which a glass pane is received, at least one edge of the glass received by the frame being covered by an edge cover member having a greater thermal conductivity than that of the glass.

2. A fire resistant glazing assembly according to claim 1, wherein the edge cover member is a metallic channel-shaped member which fits over said edge of the glass.

3. A fire resistant glazing assembly according to claim 1 or 2, wherein the edge cover member is fixed to the edge of the glass by means of a thermally conductive refractory adhesive.

4. A fire resistant glazing assembly according to claim 1, 2 or 3, wherein the edge cover member is received in the frame so that it is moveable relative thereto between first and second positions.

5. A fire resistant glazing assembly according to claim 4, wherein a suspension member is fixed to the edge cover member and is moveable therewith relative to the frame between said first and second positions.

6. A fire resistant glazing assembly according to claim 5, wherein the suspension member is moveable moves relative to a stop member of the frame in such a way that movement of the edge cover member and suspension member is limited by abutment with the stop member in said first and second positions.

7. A fire resistant glazing assembly according to claim 6, wherein there is a clearance between the edge cover member and the suspension member, the clearance receiving the stop member.

8. A fire resistant glazing assembly according to claim 6, wherein the suspension member has an elongate slot which is moveable over the stop member.

9. A fire resistant glazing assembly according to claim 6, wherein the suspension member is located in an aperture in the frame, a portion of which around the aperture acts as the stop member.

10. A fire resistant glazing assembly according to claim 9, wherein the suspension member has at least one enlarged portion greater than the size of the aperture, the enlarged portion abutting the stop member in said first or second position.

11. A fire resistant glazing assembly according to any preceding claim, wherein there is provided a beading which is fixed to the frame and captively retains the edge cover member so that it is moveable therein.

12. A fire resistant glazing assembly according to any one of claims 1 to 4, wherein the glass is suspended from a frame defined by spaced plates, a fixing passing through the plates and the glass.

13. A fire resistant glazing assembly according to claim 12, wherein the fixing comprises an outer portion which melts or disintegrates at a predetermined temperature to permit the glass to move relative to the frame and fixing until it contacts an inner portion.

14. A fire resistant glazing assembly according to claim 13, wherein the outer portion is tubular and the inner portion is a concentric metallic tube.

15. A fire resistant glazing assembly according to claim 13 or 14, wherein the outer portion is a nylon ferrule and the inner portion is a concentric metallic ferrule.

16. A fire resistant glazing assembly according to claim 1, wherein the edge cover member comprises transparent ceramic glass plates on each side of the glass edge.

17. A fire resistant glazing assembly according to claim 16, wherein the ceramic glass plates are fixed to the glass by means of ferrules that when heated become plastic to permit relative movement of the glass and the ceramic glass plates.

18. A fire resistant glazing assembly substantially as hereinbefore described with reference to each of the embodiments shown in the accompanying drawings.

19. Smoke containment apparatus comprising a fire resistant glazing assembly according to any one of claims 12 to 15.

20. Smoke containment apparatus substantially as hereinbefore described with reference to Figs. 23 and 24 of the accompanying drawings.