A grain elevator utilizing pre-cast concrete elements includes a plurality of vertical rows of bins, which slope from front to back to an angle of approximately 30.degree., the front ends of the bins being located above office, receiving, grain cleaning or shipping and agro-product warehouse space; a tower or cowl at the front end of the elevator housing bucket elevator heads and distribution conveyors for loading the bins; a discharge manifold for removing the grain from the lower, rear ends of the bins, and conveyors for delivering the grain to trucks or to bins for feeding the grain into railway cars.

BACKGROUND OF THE INVENTION 
This invention relates to an elevator for storing granular material, and in 
particular to a grain elevator. 
In the following description and appended claims, the term granular 
material is intended to mean any grain-like material such as those stored 
in silos or grain elevators. While the primary purpose of the elevator is 
for storing grain, it can also be used for storing other granular 
materials such as bulk fertilizer. 
The grain elevator art has been and is relatively static, i.e. the basic 
design of grain elevators has not changed substantially for many years. A 
search in the grain elevator art discloses little prior art. Such art 
includes U.S. Pat. Nos. 281,214, issued to W. Watson on July 10, 1883; 
867,962, issued to W. L. Finton on Oct. 15, 1907; 1,580,073, issued to W. 
O. Nothnagel on Apr. 6, 1926; and 3,931,877, issued to L. L. Albaugh on 
Jan. 13, 1976. 
One of the problems posed by existing grain elevators is that they 
represent a fire hazard. If a fire starts in one section of the elevator, 
it quickly spreads throughout the whole elevator. Another problem is that, 
in general, grain elevators, regardless of their size, are constructed 
completely on site, i.e. the entire structure is produced at the location 
where the elevator is desired. Thus, a large work force and vast 
quantities of material must be provided at the site. 
The object of the present invention is to alleviate at least partially the 
above-mentioned problems by providing a simple modular elevator structure, 
the modules of which can be prefabricated, and which prevent fire 
spreading throughout the elevator. 
SUMMARY OF THE INVENTION 
Accordingly, the present invention relates to an elevator for storing 
granular material comprising a plurality of parallel, vertically extending 
rows of inclined bins, each bin being discrete with respect to all 
adjacent bins; first wall means closing the upper ends of said bins; 
second wall means closing the lower ends of said bins; feed means for 
individually loading each bin in each vertical row at the upper end 
thereof with granular material; and normally closed discharge means for 
individually unloading each said bin in each vertical row at the lower end 
of the bin. 
More specifically, the invention relates to a grain elevator comprising a 
building defined by a base, a top wall, front and rear side walls and a 
pair of end walls; a plurality of parallel, vertically extending rows of 
bins extending between said front and rear side walls; feed means for 
individually loading each bin in each vertical row at the upper end 
thereof with grain; a normally closed discharge means for individually 
unloading each said bin in each vertical row at the lower end of the bin. 
The bins are defined by modules in the form of preformed, reinforced 
concrete sections, which are readily interconnected at a site for quick 
construction of an elevator. In the preferred form, the sections and 
consequently the bins are rectangular in cross-sectional configuration, 
with a bottom wall and integral side walls. When the sections are 
interconnected end-to-end, they form an elongated bin. A plurality of bins 
are stacked one on top of another to form a vertical row of bins, the top 
of each bin being closed by a superjacent bin, the tops of the uppermost 
bins being closed by a roof. 
In order to enable the stacking defined above, a connector is provided at 
each end of each bin section. The connector is defined by a rectangular 
bearing block at each end of and integral with each side of a bin section. 
The sides of the bearing block are parallel to the ends of the section 
side to which the block is attached. The ends of the block are inclined 
with respect to the base or web of the bin section and perpendicular to 
the ends of the sides of the bin sections. Thus, when the sections are 
stacked vertically to form inclined bins, the bearing blocks are 
vertically oriented, i.e. the sides of the blocks are disposed in vertical 
planes and the ends of such blocks are disposed in horizontal planes. 
Prefabricated end walls at the upper and lower ends of the bins incorporate 
the feed means and discharge means, respectively. The feed means includes 
a vertical passage in a precast feed manifold for each vertical row of 
bins. The discharge means includes a discharge manifold for each vertical 
row of bins, the manifold having a separate vertically extending channel 
or passage for each bin. 
Grain carried into the elevator in trucks is weighed, and then fed into 
receiving pits. 
Bucket conveyors carry the grain to the top frontend of the elevator where 
the grain is distributed along the length of the elevator by screw 
conveyors. The screw conveyors carry the grain to the top ends of feed 
chutes for feeding the grain into vertical loading passages in the precast 
feed manifolds in the front wall of the elevator. A plug is slidably 
mounted in each loading passage for successively opening feed openings in 
the upper, rear ends of the bins in a vertical row of bins. The ends of a 
chain or cable are connected to the top and bottom of the plug, the chain 
passing around pulleys or sheaves mounted at the top and bottom ends of 
the loading passage. One of the pulleys is driven by a motor or manually, 
so that the plug can be raised or lowered at will. Thus, the bins are 
loaded individually at their upper front ends. Each feed manifold also 
includes a vertical overflow discharge passage parallel to the loading 
passage. As each bin is filled, grain overflows through an overflow 
opening in the upper rear end of the bin, and passes downwardly through 
spouts to an overflow bin. Grain in the overflow bin can be recirculated, 
i.e. returned to the receiving pits to be conveyed by the bucket conveyors 
to the top of the elevator. 
The bins are unloaded into the discharge manifolds at the rear end of the 
elevator. The discharge manifolds feed the grain downwardly into discharge 
chutes, which carry the grain to a horizontal belt conveyor. The belt 
conveyor moves the grain to a shipping conveyor, and the latter carried 
the grain generally horizontally to the front of the elevator from whence 
the grain is fed upwardly via a vertical bucket elevator to one of the 
lower bins (hereinafter referred to as the shipping bin). Grain from the 
shipping bin is fed into a shipping scale for weighing, and returned to 
the top front of the elevator via the receiving pits and bucket conveyors. 
From the top front of the elevator, the grain is discharged to a truck or 
fed through a top centre discharge bin to a three-way valve at the top 
rear of the elevator, from whence the grain can be (a) discharged into box 
cars, (b) discharged into hopper cars, or (c) fed into the discharge 
manifold for return to the horizontal belt conveyor and recirculation via 
the horizontal shipping conveyor.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S) 
GENERAL DESCRIPTION OF BASIC STRUCTURE 
It should be noted that in this specification the front and rear of the 
elevator have been arbitrarily chosen to facilitate comprehension. 
With reference to the drawings and in particular to FIGS. 1 to 5, the grain 
elevator of the present invention is a building defined by a foundation or 
base 1, front and rear side walls 2 and 3, respectively, end walls 4 and 
5, respectively, and an inclined roof or top wall 6. A cowl 7 extends 
along substantially the entire length of the front wall 2 and above the 
upper front end of the roof 6. An awning generally indicated at 8 extends 
outwardly from the rear wall 3 of the building along substantially the 
entire length thereof. The awning 8 has an open bottom end, and is defined 
by an inclined top wall 9, an outer wall 10 and end walls 11. 
Except for the cowl 7 and the awning 8, which are formed of metal, the 
elevator is formed mainly of pre-cast concrete sections or panels. For 
example, the lower portion of the front wall 2 is formed by pre-cast 
panels 12. The lower area of the elevator is a service area generally 
indicated at 13 devoted to office, warehouse and retail space, weighing, 
cleaning and drying equipment and controls for operating the elevator. A 
truck (not shown) can enter door 14 (FIG. 1) at one end 4 of the building, 
unload grain and exit through door 15 (FIG. 2) in the other end wall 5 of 
the building. As described in greater detail hereinafter, trucks can be 
loaded with grain outside the front wall 2 of the elevator or train cars 
on rail siding 16 (FIGS. 2 and 4) can be loaded with grain at the rear of 
the building. The awning 8 covers the train cars during filling on the 
siding 16. The area above the service area 13 is occupied by a plurality 
of vertical rows of inclined bins generally indicated at 17 for storing 
grain or another granular material. The bins 17 are inclined from the 
front wall 2 to the rear wall 3 of the elevator. For the most part, the 
area under the front cowl 7 contains bin loading elements, and the area at 
the rear of the elevator contains bin emptying apparatus. 
As best illustrated in FIG. 5, the parallel, vertical rows of bins 17 are 
formed by overlapping the bins in one row with the bins in the adjacent 
row, i.e. by resting one bottom side edge of one bin on the top side edge 
of a bin in the adjacent parallel row of bins. Thus, the bins 17 in one 
vertical row are vertically staggered with respect to the bins in the next 
vertical row, and on the same level as the bins in the following vertical 
row. The roof 6 of the elevator is formed by two different types of panels 
18 and 19, so that the roof is inclined, with a crenelated cross-sectional 
configuration, i.e. the roof is defined by a series of parallel 
rectangular grooves alternating with parallel rectangular projections 
sloping rearwardly from the cowl 7 to the rear wall 3 of the building. 
DETAILS OF BIN STRUCTURE 
Referring to FIGS. 6 to 8, the bins 7 are formed by reinforced concrete 
sections generally indicated at 20. Each bin section 20 is in the form of 
an elongated, generally U-shaped trough defined by planar, vertical sides 
21 joined by a bottom web 22. Each side 21 includes a central panel 23. An 
outwardly projecting flange 24 extends along the top of the panel 23, a 
similar flange 25 extends along the bottom of the panel, and reinforcing 
ribs 26 extend between the flanges 24 and 25. The top flange 24 is 
provided with a small, longitudinally extending ridge 27, and the bottom 
flange includes a small, longitudinally extending groove 28. When the 
sections 20 are stacked, the ridges 27 and recesses 28 fit together to 
provide a stable seal. 
The ends of each side 21 (upper and lower ends when the section is in the 
inclined position) are provided with rectangular bearing blocks 29. The 
bearing blocks 29 are integral with the ends of the sides 21 of the bin 
section 20. Each bearing block 29 has sides parallel to the ends or sides 
of the side 21 to which the bearing block is attached. Top and bottom ends 
30 and 31, respectively of each bearing block 29 are inclined with respect 
to the web 22 and perpendicular to ends 32 of the sides 21, so that when 
the bin sections 20 are stacked vertically to form inclined bins 17, the 
bearing blocks 29 are vertically oriented for supporting the maximum load. 
The top end 30 of each bearing block 29 is provided with a cylindrical 
recess 33 for receiving a pin 34 in the bottom end of a superjacent 
bearing block 29. Of course, other forms of connectors can be used 
including the use of cast in place of concrete sections. Also, a recess 
can be provided in the top and bottom of each bearing block 29, and dowels 
inserted in the recesses to connect the bin sections. 
GRAIN RECEIVING APATUS 
Referring to FIGS. 9 to 11, a truck (not shown) carrying grain upon 
entering the building stops on a truck scale 35. A grain scale 36 is 
mounted on a support 37 in the area of the truck lane. As described in 
greater detail hereinafter, grain being weighed (for discharge) passes 
downwardly from the scale 36 via arms 38 and 39 of a chute 40 into the 
receiving pits 41 and 42. Grain from the truck is dumped into one of 
receiving pits 41 or 42. Grain flowing from the bottom of the receiving 
pits 41 or 42 enters one arm or front leg 43 of vertical bucket elevator 
44 or 45. The bucket elevators 44 and 45 contain bucket conveyors (not 
shown) for carrying the grain to the top of the elevator, i.e. upwardly 
into top end 46 of the cowl 7. The conveyor travels up the arm 43 and 
returns to the bottom of the elevator via arm 47. 
Grain is discharged from the top ends of bucket elevators 44 and 45 via 
nozzles 48 in top hoods 49 and three-way valves 50. Upon leaving the 
three-way valves 50, the grain is fed (i) via ducts 51 and a feed box 52 
to screw conveyors 53 and 54 in casing 55 for filling all but the central 
bins 17, (ii) via ducts 56 and a two-way valve 57 to the central vertical 
row of bins or a truck, (iii) via ducts 58 direct to the screw conveyors 
53 and 54. The locations of the front, upper ends of the nine vertical 
rows of bins 17 are numbered 59 to 67. Grain passing through the ducts 51 
and the feed box 52 or through the ducts 58 enters the casing containing 
the screw conveyors 53 and 54, and is carried by the conveyors 53 and 54 
to the top ends of chutes 68. The chutes 68 feed the grain into the rows 
59 to 62 and 64 to 67 of bins. The conveyors 53 and 54 are driven at their 
outer ends. A service platform 69 (FIGS. 12 and 13) is provided at the 
hood end of the two vertical bucket elevators 44 and 45. Motors 70 for 
driving the bucket conveyors in the pipes 44 and 45 are mounted on ledges 
71 on the sides of the pipes 44 and 45 above the platform 69. 
With reference to FIGS. 15 and 17 to 20, the inner front wall is defined by 
concrete panels 70, each of which includes a planar vertical web 71 and 
inwardly extending vertical partitions 72. By attaching plywood panels 73 
to the inner edges of the partitions 72, a feed manifold containing 
vertical extending passages is formed. One passage 74 of each manifold in 
front oe each vertical row of bins is used as a grain feed passage. Grain 
from a screw conveyor 53 or 54, or from two-way valve 57 passes through a 
gate 75 (FIGS. 12 and 16) on the bottom of the screw conveyors 53 and 54 
and then through chutes 68 downwardly into the top end of passage 74. Each 
passage 74 is provided with a rectangular plug 76 which substantially 
fills the passage, preventing the passage of grain. A cable 77 connected 
to the top end of the plug 76 passes around a pulley 78 mounted above the 
passage 74 in the cowl 7, downwardly through an adjacent passage 79, 
around a pulley 80 mounted at the bottom end of the panels 70 and upwardly 
in the passage 74 to the bottom end of the plug 76. A reversible motor 
(not shown) is connected to the pulley 78 for moving the plug 76 down or 
up. Alternatively, the plug 76 can be manually raised or lowered using a 
handle (not shown) connected to the pulley 80. A counterweight 81 on the 
cable 77 in the passage 79 facilitates movement of the plug 76. Flags 82 
on the cable 77 provide an indication of the location of the plug 76, and 
may be used to activate sensors or switches as part of an automated 
control system. 
The plywood panels 73 form covers over the upper, front ends of the bins 
17. In each vertical row of bins, a feed opening 83 from the passage 74 is 
provided in the plywood panels 73 at the top end of each bin 17. The feed 
opening 83 is normally closed by a gate 84. An overflow opening 85 is 
provided below the top end and above the bottom end of each feed opening 
83 in the panels 73. The openings 85 connect the upper end of the bins 17 
to overflow passages 86 in the feed manifold adjacent to the feed passages 
74. Thus, when a bin 17 becomes filled with grain, the grain overflows 
through the opening 85 into overflow passages 86. The grain passes 
downwardly to the lower ends of the feed manifolds where it is discharged 
through spouts 87 into overflow bins 88 (FIG. 21). Discharge ducts 89 at 
the bottom ends of the overflow bins 88 provided with gates 90 feed the 
grain back into the bucket elevators 44 and 45 for return to the top of 
the elevator. 
Grain entering the bins 17 flows downwardly from the upper front end 
thereof to the lower rear end thereof. Upon reaching the lower rear end, 
the grain slides down a spout 100 on the outer end of the lowermost bin 
section into a discharge manifold 101 (FIG. 22). The spouts 100, which are 
formed on the lowermost bin sections only, are merely V-shaped central end 
portions of the bin sections. Each vertical row 59 to 67 of bins 17 is 
provided with a discharge manifold 101. The discharge manifolds 101 are 
somewhat similar to the feed manifolds. Each discharge manifold 101 
includes an inner wall panel 102 and an outer wall panel 103 (FIG. 3). 
Partitions 104 extend between the inner and outer panels 102 and 103, 
forming discharge passages 105 to 109. In one vertical row of bins, e.g. 
row 60 or 62, an opening (not shown) in panel 102 from uppermost bin 110 
discharges into 105, an opening from the next bin 111 opens into the 
passage 109, bin 112 opens into the passage 106, and bin 113 opens into 
the passage 107. In the adjacent row of bins, e.g. row 59 or 61, the bins 
(from top to bottom) open into passages 105, 109, 106, 108 and 107, in 
that order. In order to effect the discharge pattern just described 
diagonal dividing walls 114, 115, 116 and 117 are provided in the manifold 
101. The uppermost diagonal wall 114 extends between the third (from the 
left) vertical partition and the first partition, with a gap between 
bottom ends of the first and second vertical partitions above the diagonal 
wall 114 and the top of such diagonal wall. The next diagonal wall 115 
extends between the second and fourth vertical partitions in a gap in the 
third and fourth vertical partitions. The second wall 115 slopes in the 
opposite direction to the wall 114. The last two diagonal dividing walls 
116 and 117 extend between the second and third walls, one inclined in one 
direction and the other in another direction. The result is gaps in each 
vertical partition through which grain can flow from one and only one of 
the bins 17. Grain from the lowermost bin 113 flows downwardly from 
beneath the lowermost diagonal wall 117 straight out of the lowermost 
diagonal wall 117 straight out of the lowermost bin through passage 107. 
In effect, the vertical partitions and diagonal dividing walls define a 
maze-type discharge manifold, which permits the flow of grain from one bin 
only. It will be noted that in both cases illustrated in FIG. 22, the 
chute 100 at the bottom of each bin 17 is aligned with one passage 105 to 
109 only. 
There is no gate closing the opening at the lower ends of the bins 17, i.e. 
the bins open directly into the passages 105 to 109. Thus, when the bins 
17 are being filled, grain flows downwardly into the manifold 101 and 
fills discharge spouts 118 (FIGS. 9 and 10) at the bottom ends of the 
discharge manifold. The spouts 118 extend inwardly to the casings of belt 
conveyors 119 and 120. A simple slide gate 121 (FIG. 10) is provided at 
the junction between the bottom end of each spout 118 and the casings of 
the conveyors 119 and 120. The slide gates 121 are also controlled by the 
automated control system. 
The conveyors 119 and 120 transport the grain inwardly to a shipping belt 
conveyor 122 (FIGS. 9 to 11 and 23). The conveyor 122 carries the grain 
forwardly at the bottom of the elevator to a vertical bucket elevator 123, 
which is beside and parallel to the vertical bucket elevator 45. As shown 
in FIG. 10, the bucket elevator 123 has two legs 124 and 125 for housing a 
bucket conveyor (not shown), which moves the grain upwardly to a hood 126 
for discharge into a two-way valve 127 (FIGS. 10 and 27). Grain passing 
through the valve 127 is fed (i) into a pipe 128 for loading a truck 
outside the front wall 2 of the elevator, or (ii) through a pipe 129 to 
one of the bins 17, which is designated the shipping bin and is identified 
by reference numeral 130 in the drawings. Minor discrepancies have been 
left in the foregoing description of the bins 17 to avoid confusion. The 
bin 130 is not filled with the other bins, but is used exclusively as a 
shipping bin. The same applies to top central bin 131, (FIG. 5) which is a 
discharge bin, as described in greater detail hereinafter. 
Grain in the shipping bin 130 is discharged through a bottom gate (not 
shown) in the bin into a spout 132 for carrying the grain to the scale 36. 
A gate 133 is provided in the spout 132 for controlling the flow of grain 
to the scale 36. After weighing, grain is again fed through the receiving 
bins 41 and 42, returned to the upper top end 46 of the cowl 7, and 
discharged through the spouts 48, three-way valves 50, ducts 56 and 
two-way valve 57 to the centre row of bins and then to the top, central 
discharge bin 131. 
As shown in FIGS. 24 to 26, the bottom of the bin 131 at the lower rear end 
thereof is continued through the manifold 101 to the outer rear wall of 
the elevator. To this end, a concrete plug 134 is provided in the manifold 
101. An opening 135 in the outer wall 103 of the manifold 101 permits the 
discharge of grain through a chute 136 into a three-way valve 137. The 
opening 135 is normally closed by a gate 138 slidably mounted in tracks 
139 defined by slots in the sides of a guide bracket 140 mounted on the 
outer wall 103 of the manifold 101. The gate 138 is moved between the open 
and closed positions by a fluid actuated cylinder 141, the piston 142 of 
which is connected to the upper end of the gate 138. The three-way valve 
137 permits the flow of grain to one of (i) a hopper car 143 (FIG. 24) on 
the rail siding 16 via an outlet duct 144, (ii) a boxcar (not shown) via 
an outlet duct 145 or (iii) a passage 105 in the discharge manifold 101 
via a spout 146 and an inlet 147. 
It should be noted that while the bin 131 (the top centre bin) has been 
described as the discharge bin, any or all of the top bins in the vertical 
rows 59, 61, 63, 65 and 67 (FIG. 5) can be used as discharge bins. 
OPERATION 
For the most part, the operation of the elevator is described piecemeal in 
the foregoing. For the sake of completeness, the operation will now be 
described with reference to FIG. 27. 
Grain carried into the elevator in a truck 148 is dumped into receiving 
pits or bins 41 and 42. From the bins 41 and 42 the grain travels upwardly 
to the three-way valves 50 at the upper front end of the elevator. From 
the three-way valves 50, the grain flows through ducts 51 or 58 into the 
conveyors 53 and 54 for distribution to the bins 17 in vertical rows 59 to 
62 and 64 to 67, or through two-way valve 57 to the central row 63 of bins 
or to a truck 149. The bins 17 are filled sequentially with grain via the 
feed manifolds. As the bins 17 are filled, the grain also fills the 
discharge manifolds 101. When the slide gates 121 at the bottom of the 
spouts 118 are opened, grain is fed onto the belt conveyors 119 and 120. 
The gates 121 can be opened selectively, i.e. individually or en masse. 
The conveyors 119 and 120 feed the grain to the shipping conveyor 122, 
which carries the grain to the vertical bucket elevator 123. From the 
bucket elevator 123, the grain enters the shipping bin 130, and is 
transferred to the scale 36 for weighing. The grain then travels back to 
the receiving bins 41 and 42, through bucket elevators 44 and 45 to the 
top front end of the elevator, and through the ducts 56 to a feed box 57. 
From the feed box 57, the grain enters the discharge bin 131, and from the 
bin 131, the grain passes through the three-way valve 137 to a hopper car 
143 or a boxcar 151. 
SUMMARY 
There has thus been described a modular elevator for grain or other 
granular material formed predominantly of precast concrete. The elevator 
is capable of extremely high throughput, is flexible in terms of capacity, 
and is relatively efficient. 
While not mentioned hereinbefore, the slope of the bins may be important 
depending on the type of material being stored in the elevator. The usual 
slope of the bins is 30.degree.. However, any slope above 22.5.degree. is 
acceptable for filling, the preferred range of slope being 22.5.degree. to 
30.degree.. Emptying can be effected over a wide range of slopes, except 
that a thin layer of grain is left on the bin floor with lesser slopes. If 
left in the bins, such grain could contaminate the subsequent contents of 
the bins. Dry barley left no residue for slopes exceeding 28.degree., but 
tough barley requires a slope of approximately 30.5.degree. to completely 
clear the residue. Since tough barley is wetter than would be accepted, a 
slope of 30.degree. should be adequate. 
In practice, the structure described hereinbefore and illustrated in the 
drawings is intended to have a storage capacity of approximately 206,000 
bushels. Additional modules can be added either during or after 
construction to increase the capacity of the elevator. The first such 
additional module would be added at the front of the base structure to 
increase storage capacity and provide a second driveway with a second 
receiving scale. Additional modules of approximately 55,000 bushel 
capacity could be added to either end of the elevator. The possibility of 
expanding the elevator makes the building suitable for handling grain in 
any farm community. 
Additional features of the invention described hereinbefore include the 
fact that grain cars can be loaded relatively quickly. Moreover, unlike 
conventional elevators, virtually all bin space is utilized. The use of a 
pre-cast structure is relatively adaptable. By suitable arrangement of 
transfer equipment, i.e. the loading and unloading devices, entirely 
different commodities such as grain and bulk fertilizer can be handled in 
a single elevator in much the same manner as they would be handled in 
separate structures. The use of sloping bins in the elevator eliminates 
overpressures due to charging and discharging. 
While they have not been described in detail because they do not form part 
of the present invention, cleaning and drying equipment, and office, 
warehouse and retail space are provided in the lower part of the elevator. 
While the elevator is no bigger than a conventional double composite 
170,000 bushel capacity elevator, it is still capable of storing 206,000 
bushels of grain. The manager of the elevator can carry out all elevator 
business from one central location. Such business includes the weighing 
and receiving of grain, operating elevator controls, and sales. By 
maintaining the air pressure in the office and warehouse areas higher than 
in the driveway, an acceptable dust-free environment can be maintained. 
Finally, the elevator structure is designed to reduce the danger of fire or 
explosion to a minimum. The use of pre-cast concrete sections closed by 
concrete panels at each end is important. An explosion in one bin could 
break the wall panel at the end of such bin free of the remaining 
structure, and, if enough force was generated, blast the panel through the 
metal siding. However, if a fire or explosion occurs in one area, damage 
is restricted to such area and does not readily spread to the remainder of 
the elevator.