Table 5.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from roof bolting machinery
accidents by mine size and seam height, 1990-94

Mine size (No, of employees)

Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Low... 136 «1.09 3031.21 103—*1.28 68 72 ~«610~—«1<.47
Medium . 72 1.43 224 1.08 201 1.27 173° 77 = 6701.02
High .. 16___67 90.83 65___78 2068746784
Overall. 224 1.05 617 1.09 3691.15 537.81
14
{BB Low seams
12. SQ Medium seams
High seams
2 10. — — Overall rate
3 within mine size
3
2
$ —
S os
Ss
=
a
§ os 7
2
&
5
© 04 |
024 HH
00:
<20 20-49 50-99 >99
Mine size (Number of employees)
Figure 16.—Rate of nonfatal disabling injuries from roof bolting machinery accidents by mine size and
‘seam height, 1990-94.
Table 6.—Number and rate (per 200,000 hr) of nonfatal injuries from roof-bolting machinery
accidents by mine size and seam height, 1989-95
Mine size (No. of employees)
Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Low. 1 006 3 -009 0 = 0 = 4.005
Medium . 1 011 1 004 2 .009 2 .006 6 .006
High .. 0 - ) - 0 - 1.002 1 001
Overall. 2 007 4 005. 2.004 3.003



of less than 42 in may apply for exemption from the require-
ment for canopies. Of the 80 roof fall fatalities, 9 involved
miners operating equipment without a canopy. Seven of the
nine fatalities occurred in low seams; two, in medium seams.
Although there appeared to be little relation to seam height
for accidents involving handling materials, continuous mining
machines, and powered haulage locomotives, variations related
to mine size were observed in the injury rates for these
accidents. Nonfatal disabling injury rates for material handling
accidents showed substantial increases with increasing mine
size within every level of seam height (refer to figure 14). For
accidents involving continuous mining machines, both fatal and
nonfatal injury rates decreased as mine size increased (refer to
figure 19). This is particularly significant given that exposure
hours to this type of equipment are probably inflated for smaller
mines, which are more likely to employ both conventional and
continuous mining methods. The injury rates for accidents

involving powered haulage locomotives were substantially
higher for mines with 50 or more employees than for those with
fewer than 50 employees. This latter difference is not un-
expected given that this type of powered haulage is more
prevalent in larger mining operations.

In summary, nonfatal disabling injury rates for accidents
involving slips/falls, shuttle cars, and ground falls increased as
seam height increased. On the other hand, nonfatal disabling
injury rates for accidents involving load-haul-dumps, personnel
arriers, powered haulage conveyors, and roof bolting machines
decreased as seam height increased. For mines with fewer than
50 employees, fatal injury rates for accidents involving falls of
unsupported mine roof decreased as seam heights increased.
Finally, a disproportionate number of fatalities from accidents
involving shuttle cars and roof bolting machines occurred in
low- and medium-seam heights.

DISCUSSION

The working height of an underground bituminous coal mine
can directly affect safety in a number of ways. As the working
height decreases to the extent that miners must stoop, duck, or
crawl, the miners’ vision, posture, and mobility become
increasingly restricted. The increased physical demands placed
on the miner working in low-seam heights may be reflected in
the younger ages observed for miners injured in low-seam
mines. Additionally, as mining height decreases, the mine roof
increasingly becomes an additional source of injury to the
miner. Although equipment is sized proportionally for thinner
coal seams, the height restriction puts limitations on placements
of operator compartments and affects what and how much an
‘operator can see while in the cab. Lower mining heights can
also make tasks more difficult to perform, such as requiring a
roof bolter operator to bend and unbend long roof bolts in order
to insert them into the mine roof. A safety concern at medium-
seam operations is posture. Miners working at these heights
cannot lift by using the traditionally advocated safe lifting
procedures. Laboratory studies of the effects of lifting materials
using different postures (¢.g., kneeling, stooping, etc.) suggest
that working heights in the medium range (about 48 to 72 in)
are more stressful on the back than those that require a person

to remain kneeling or that allow a person to stand [Gallagher et
al. 1995]. Reduced mobility is another concern in lower seam
heights. Miners who must duck walk or crawl from place to
place within their work area may be moving more slowly and
with greater expenditure of energy than those who are free to
walk upright or even run if the situation requires. On the other
hand, this increased mobility can also create problems, as
shown by the increased rate of slip and fall injuries in higher
seam heights. Visibility, limits to mobility, and posture
restrictions can all affect miners’ safety and health. To
appropriately focus prevention efforts for the underground
bituminous coal industry, statistical analyses of injury data can
provide direction for more detailed research. On the basis of
this preliminary analysis, the effects of mining height warrant
further investigation involving a more detailed examination of
the injury records, as well as task analyses of mining activities
such as roof bolting in various mining heights. Additionally,
more information regarding the amount of exposure to different
types and makes of equipment is required to determine whether
differences in the rates of injuries for machinery and powered
haulage accidents are directly or indirectly related to differences
in mining height or mine size, or both.


Low
2 seams
= Medium
= 6 5 Me
2 oe
—
5 Zz High
3 O seams
£ 6.3
Be N=3411
S
: 5 55
g
® 4 \ 4 4
34 39
§ 3 3
Q 25
5
82
3
=
0. T
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 9.—Distribution by mine size and seam height of the median years of experience in current

job classification for miners injured in 1994,

RELIABILITY OF SEAM HEIGHT DATA

To determine the relationship between mining height and the
types and rates of injuries in underground mines, obtaining the
actual working height of the mine at the scene of the injury
would be ideal. This information, however, is not usually
available unless a fatality occurs. Actual mining height at the
scene of the accident is documented for most underground
fatalities as part of the information detailed in the investigation
report. Although MSHA’s database for underground coal mine
operators contains a field listing the average height of the coal
seam currently being mined, the difference between this height
and the actual mining height may vary considerably between,
as well as within, sections of a mine.

Preliminary analyses were conducted to determine whether
the average seam heights recorded in the database were accurate
enough to identify trends in injury rates related to mining height
differences. These analyses involved the selection of a subset

of the nonfatal disabling injuries for which the miner’s activity
at the time of injury was coded as walking/running or crawling/
kneeling. The expectation was that the rate of injury to miners
whose activity was classified as walking or running at the time
of injury would increase as seam heights increase. Conversely,
the rate of injury to miners whose activity was classified as
crawling or kneeling at the time of injury should decrease as
seam heights increase. Additionally, these trends should be
evident regardless of the size of the mining operation. The
results of these analyses are summarized in tables 1 and 2 and
graphically displayed in figures 10 and 11. As expected, the
rate of injury to miners walking or running when injured
increases as seam height increases. Similarly, the rate of injury
to miners crawling or kneeling at the time of injury decreases as
seam height increases. Both of these trends are evident across,
as well as within, categories of mine size.

Table 1.—Number and rate (per 200,000 hr) of nonfatal disabling injuries for miners walking/running
at time of injury by mine size and seam height, 1990-94

Mine size (No. of employees)
50-09

‘Seam height <20 20-49 399 ‘Overall
No. Rate No. Rate No. Rate "No. Rate" No.__Rale
24 «19 84 34 33 ~41~=C«*00.~S~*«« SCC
3458 116 56 12200 77) 2831.25 5558S.
18 75 4081.00 81.97 600.76 8071.45
76. 36. 308 55 236.73 9831.49



Shuttle Cars

Nonfatal disabling injury rates related to the use of shuttle
cars are lowest in low seams both overall as well as within each
category of mine size (see table 9 and figure 21). Additionally,
a trend of increasing injury rates with increasing seam height is
particularly evident for the smallest mine size. A similar, but
weaker trend appears for the largest mine size as well. Fatal

injury rates, however, show an overall decrease with increasing
seam height (see table 10 and figure 22), Although small mines
operating in low coal had the lowest nonfatal disabling injury
rates (.29), they had the highest fatality rate (017). Of the 14
fatalities involving shuttle cars, 12 (86%) occurred in low or
medium mining heights. As noted previously, these mines
accounted for 69% of the underground employee hours.

Table 9.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from shuttle car haulage
accidents by mine size and seam height, 1990-94

Mine size (No_ of employees)

‘Seam height <20 50-99 399 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Tow 36 ~«28 110.44 4353 49 «452 288.
Medium . 37 5B 143 69 130071 133 5942685
High... 774 7267 45 5423469868
Qverall_. 9042 32557 20162416 63
08
FB Low seams
or IN — Medium seams
(1 High seams
f LT
2° J — Overall rate
g IN VY within mine size
£
§ os. +
8
J
8
S 04 H
a
8 os H
=
5
=
024 +H
os} H
00 T
<20 20-49 50-90 >99
Mine size (Number of employees)
Figure 21.—Rate of nonfatal disabling injuries from shuttle car haulage accidents by mine size and seam
height, 1990-94.
Table 10.—Number and rate (per 200,000 hr) of fatal injuries from shuttle car haulage
accidents by mine size and seam height, 1989-95
Mine size (No. of employees)
Seam height =20 20-49 ‘50-99 399 ‘Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Tow. 3 017 1 003 1.009 1.008 6.008
Medium . .. sees 1 ott 2 007 1.004 2.006 6  .006
High .... 0... 0 - 0.020 1.009 4.002 2.003
Overall. 4013 3.008 3.007 4.004



11.
12.
13.

20.
21.

22.
23.
24.

25.

TABLES—Continued

Number and rate (per 200,000 hr) of fatal injuries from shuttle car haulage accidents by mine size and seam
height, 1989-95... ....eeceeeceeeeeeeeeeees
Number and rate (per 200,000 hr) of nonfatal disabling
mine size and seam height, 1990-94
Number and rate (per 200,000 hr) of fatal injuries from load-haul-dump haulage accidents by mine size and
seam height, 1990-94 .
Number and rate (per 200,000 hr) of nonfatal disabling injuries from personnel carrier haulage accidents by
mine size and seam height, 1990-94

seam height, 1990-94.
Number and rate (per 200,0
mine size and seam height, 1990-94
Number and rate (per 200,000 hr) of fatal injuries from powered haulage conveyor accidents by mine size
and seam height, 1989-95
Number and rate (per 200,000 hr) of nonfatal disabling injuries from locomotive accidents by mine size and
seam height, 1990-94
Number and rate (per 200,000 hr) of nonfatal disabling injuries from slips or falls by mine size and seam
height, 1990-94
Number and rate (per 200,000 hr) of nonfatal disabling injuries from falls of roof by mine size and seam
height, 1990-94 veces
Number and rate (per 200,000 hr) of fatal injuries from falls of roof by mine size and seam height, :
Number and rate (per 200,000 hr) of fatal injuries from falls of supported roof by mine size and seam height,
1989-95 o.oo e eee eeeeeee eee ees
Number and rate (per 200,000 hr) of fatal injuries from falls of unsupported roof by mine size and seam
height, 1989-95
Number and rate (per 200,000 hr) of nonfatal disabling injuries from falls of rib by mine size and seam
height, 1990-94.
Number and rate (per 200,000 hr) of nonfatal disabling injuries from machinery-related falls of groun
mine size and seam height, 1990-94
Number and rate (per 200,000 hr) of nonfatal disabling injuries from the use of nonpowered hand tools by
mine size and seam height, 1990-94... .

20

20

21

21

22

23

24

26
26

26

26

28

29

29


Table 24.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from machinery-related falls
of ground by mine size and seam height, 1989-95

Mine size (No. of employees)
50-99

Seam height <20 20-49 299 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Tow .. 112.90 205 ~~ 82 6479 62 «66 443°~« BT
Medium . 490077 199.96 130.82 159.70 537.82
High . ceeteeees 19.79 107__—.99 6679318 3, 510.92
Overall 180.85 S11 20 260.81 539 82
10 —
— || Bf Low seams
Medium seams
0.8 —= — — | [1] High seams
2 — Overall rate
5 within mine size
co
2
8 o6- 4 H
io
s
8
S
g
F044 H
®
2
5
=
02+ H
004 T T T
<20 20-49 50-99 >99
Mine size (Number of employees)
Figure 33.—Rate of nonfatal disabling injuries from machinery-related falls of ground by mine size
and seam height, 1990-94,
Table 25.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from the use of nonpowered
hand tools by mine size and seam height, 1990-94
Mine size (No. of employees)
Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No. Rate No. Rate" No.__Rate
Tow. 90 «72 222 ~~. 89 74 «92 96 1.02 482 ~~. 88
Medium . 4 64 167.80 13585 189.840 5328
High . 16 87 101___—. 93 5971 337.99 513.92
Overall. 147.69 490 87 268.83 131.94



ora.

Bh Low seams

) Medium seams.

0.008.

1 High seams

— Overall rate
within mine size

0.004:

Fatalities per 200,000 hours
H

0.000: T

<20 20-49

Mine size (Number of employees)
Figure 17.—Rate of fatal injuries from roof bolting machinery accidents by mine size and seam height,

1989-95.
Continuous Miner Machinery Accidents

Although injuries related to the operation of continuous
mining machines account for only 15% of the nonfatal disabling
machinery-related injuries, they account for 54% of the fatal
machinery-related injuries. It is important to bear in mind that
variations in injury rates for accidents involving continuous
mining machines will reflect, in part, variations in exposure to
continuous versus conventional mining methods because the
latter do not employ these machines. Because apparent ex-
posure to continuous mining machines increases both as seam
height and mine size increases (refer to figure 5), injury rates
may be expected to increase as well. Contrary to expectations,

nonfatal disabling injury rates decrease slightly overall as seam
height increases and more substantially as mine size increases
see table 7 and figure 18). Additionally, the single highest
nonfatal disabling injury rate (.36) is observed for the smallest
mines working in the lowest seams. Mines in this category had
the highest percentage of injuries related to conventional mining
methods (19%). Similar to the trend observed for nonfatal
disabling injury rates, fatal injury rates related to continuous
miners decrease overall as mine size increases (see table 8 and
figure 19). However, as seam height increases, fatal injury rates
also show an overall increase. Although the numbers are small,
this trend is relatively persistent for all but the smallest mines.

Table 7.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from continuous miner machinery

accidents by mine size and seam height, 1990-94
Mine size (No. of employees)
‘Seam height 20 20-49 50-99 399 ‘Overall

No Rate No. Rate No. Rate No. Rate__“No._ Rate
iow... 45.36 63 —~25 724 17 18 14226
Medium . 12 19 5426 4830 36 16 = 150.23
High .. 729 27 25 1113 54.16 99.18
Qverall 64.30 144 25 7624107 16



Injuries per 200,000 hours

TE Low seams

os Medium seams
(7 High seams
— Overall rate

within mine size

04

os LI

0.24 |

on} H

00 T T

20-40
Mine size (Number of employees)

>a

Figure 24.—Rate of nonfatal disabling injuries from personnel carrier haulage accidents by mine size
and seam height, 1990-94.

Table 14.—Number and rate (per 200,000 hr) of fatal injuries from personnel carrier haulage
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)
50-99

‘Seam height <20 20-49 >99 ‘Overall
No. Rate No. Rate No. Rate__"No. Rate No.__ Rate
Tow... 0 = 0 = 0 = 1.008 1.001
Medium . 0 - 1 004 1.004 ° - 2 002
High . 0 = o = 4.009 o = 1.001
Overall. 0 = 1.004 2.004 1.007

Conveyors

Overall, nonfatal disabling injury rates involving powered
haulage conveyors decrease with increasing seam height (see
table 15 and figure 25.) Although this trend persists for only
the smallest and largest mine sizes, the highest rates are

consistently observed in low seams for every mine size.
Although few in number, it is worth noting that of the five fatal
injuries involving powered haulage conveyors, none occurred
in low seams, However, 4 of the 5 (80%) occurred in mines
with fewer than 50 employees, which account for only 44% of
the employee hours (see table 16).

Table 15.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from powered haulage conveyor
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)

‘Seam height <20 20-49 50-99 399 ‘Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Tow... 446 35 96 38 38 CAT 7 18 195 35
Medium . 19.30 330016 19.12 2 96 15
High . ceeeeeees 437 4716 19.23 21.06 ett
Overall 8D 146 6 6.24 63.10



0.020:

EE bow seams
Medium seams
(7 High seams

2

— Overall rate
within mine size

Fatalities per 200,000 hours
e
2

Yy

0.000.
<20

20-49

50-99 >99

Mine size (Number of employees)
Figure 19.—Rate of fatal injuries from continuous miner machinery accidents by mine size and seam

height, 1989-95.

POWERED HAULAGE ACCIDENTS

trams, etc., (3) personnel carriers, such as man cars, man trips,
etc., (4) conveyors of all types, stationary or mobile, or

Most of the nonfatal disabling injuries (93%) and all except _(5) locomotives (see figure 20). Nonfatal disabling and fatal
one of the fatal injuries resulting from powered haulage injury rates for each of these five types of equipment are
accidents involved one of five types of powered haulage examined separately below.
equipment: (1) shuttle cars, (2) Ioad-haul-dumps, scoops,

Nonfatal injuries

Fatal injuries CO Shuttle car
EE toad nautcum

ey Personne
carer

EB) conveyor
FB Lecomatve

Wl otter

48%

Figure 20.—Nonfatal disabling injuries (1990-94) and fatal injuries (1989-95) by type of equipment involved

in powered haulage accidents,


12.
TB Low seams
to Medium seams
— 7 High seams
e — Overall rate
g within mine size
3 os: Ly
£
Ss
8
ba
8
S 06. +
3
a
8
5 04 +
=
oz. [|
00 1

20-49

50-99

Mine size (Number of employees)

Figure 34.—Rate of nonfatal disabling injuries from the use of nonpowered hand tools by mine size and

seam height, 1990-94.

SUMMARY

Few of the trends in injury rates across seam height
described in this report were as strong as those observed in the
preliminary analysis of injuries related to the activities of
walking/running and crawling/kneeling. The most consistent
trend in injury rates associated with differences in seam height
was observed for nonfatal disabling injury rates for accidents
involving load-haul-dump types of powered haulage equipment
(refer to figure 23). For these types of accidents, injury rates
declined as scam height increased within every category of
mine size. However, the strength of the trend also decreased as
the size of the mining operation increased. As discussed
previously, using mine-level average coal seam heights to
approximate actual mining height at the scene of an accident
may become less reliable as the size of a mining operation
increases. This may explain why injury rates for accidents
involving slips/falls and rib falls did not show the expected
increases within the largest mine size category (refer to figures
27 and 32, respectively). Despite these aberrations, the trends
in injury rates for several categories of accidents suggest a
relationship, whether direct or indirect, to mining height.

In several cases, although a steadily increasing or decreasing
trend was not observed within each mine size category, the
highest or lowest injury rates were consistently observed within
one level of seam height across all mine sizes. For example, the
lowest rates of injuries involving shuttle cars and the highest
rates of injuries involving powered haulage conveyors were
observed in low seams across all mine sizes (refer to figures 22
and 25, respectively). Similar, but less consistent observations

were made for several other types of accidents. Both fatal and
nonfatal injury rates for machinery accidents involving roof
bolters were lowest in high seams, except for the largest mines
(refer to figures 16 and 17, respectively). Additionally, nonfatal
injury rates increased with increasing seam height for mines
with 20-49 and 50-99 employees. The highest rates of injuries
involving powered haulage personnel carriers were also
observed in low seams, again except for the largest mines (refer
to figure 24). The highest rates of nonfatal injuries resulting
from falls of roof were observed in the highest seams, except
for mines with 50-99 employees (refer to figure 28). Ad-
ditionally, these rates increased with increasing seam height for
both the smallest and largest category of mines.

‘The distributions of fatal injury rates for accidents involving
falls of the mine roof varied considerably depending on whether
the victim was positioned under supported or unsupported roof.
Rates of fatal injuries resulting from falls of supported roof
showed no consistent trend relating to changes in seam height,
but showed a marked relationship to changes in the employment
size of the mine (refer to figure 30). Although fatal injury rates
associated with falls of unsupported roof showed a similar
relationship to mine size, for mines with fewer than 50 em-
ployees the trends appeared to be related to changes in seam
height (refer to figure 31). Previous researchers have suggested
various reasons why miners working in low seams may be more
likely to venture under unsupported roof [Peters and Fotta
1994a]. One contributing factor may be the absence of
protective canopies on equipment. Mines operating in heights


RESULTS

In the following sections of this report, the distributions of
nonfatal disabling injury rates in the United States across both
mine size and seam height are presented for the six major
accident classifications. The sections are ordered from the most
frequently occurring class of accidents (handling materials) to
the least frequently occurring accident type (hand tools). The
distributions of fatal injury rates are reported for accidents
classified as ground falls, machinery, or powered haulage. Both
figures and tables are used to identify and describe variations
and trends in the rates of injuries with regard to both seam
height and mine size. The tables contain the actual numbers of
injuries and the corresponding rates (injuries per 200,000
employee hr). A summary of the findings follows the
presentation of data.

HANDLING MATERIALS ACCIDENTS

Handling materials injury rates increase slightly overall as
seam height increases (see table 3). Within levels of mine size,

this trend is observed only for the smallest mines (see figure
14). The variations in these rates appear to be more strongly
related to mine size, increasing as mine size increases. A more
focused analysis was obtained by examining the subset of the
data for which the part of the body injured was reported to be
the back (see table 4 and figure 15). Back injuries accounted
for 55% of the injuries sustained while handling materials
during the 5-year period. Similar to the trend observed for all
handling material injuries, the rates of back injuries increase as
mine size increases and show no obvious relation to variations
in seam height.

MACHINERY ACCIDENTS

A closer examination of the injury records within the
accident classification of machinery revealed that the actual
source of the disabling injury for 37% of the accidents was
coded as "caving rock” that had fallen from either the mine roof
orrib. The miner involved was either operating or assisting in

Table 3.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from handling materials
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)
50-99

Seam height 20 20-45 399 Overall
No, Rate No. Rate No. Rate No. Rate No. Rate
iow. 3682.95 901 3.6t 365 «453 ~~ ~«542 «5.75 2,176 3.96
Medium 222 3.49 840 4.05 742 469 1,089 4.83 2,893 4.42
High . 903.75 4133.82 3133.76 1,790 5.26 2,606 _4.69
Overall 6803.20 2.154 3.81 1.420 4.41 3.421 5.18
60
FB Low seams
s0 | SY Medium seams
1 High seams
2 — Overall rate
5 within mine size
3 40 iN H
s —
3
3
s
8 20 L|
i]
a
ry
2
5 20 4
2
10 +
00
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 14.—Rate of nonfatal disabling injuries from handling materials accidents by mine size and seam

height, 1990-94,


80

Low
52% | seams
<] Medium
|_| BS seams
oO High
44% seams
i=
£& 34%|
37%
$40 HH L
2
© 49%
o
>
2 59%
F oo 19% 142 | |
25% | 26%
30%
11%
OF T T T
<20 20-49 50-99 >99

Mine size (Number of employees)

Figure 2.—Number and percent (within mine size) of underground employee hours by mine size
and seam height for nonlongwall bituminous coal mines, 1990-94.

3007537
Low
seams
250" Medi
S) ium
seams
. High
g 2004 a7 CO seams
£& =
= 22% N=1,071
© 150+ 35%
oO
2
£
3
= 1004 ae
18%
50+ 10%
33% 36% 350 35% 422
0+

T T T
<20 20-49 50-99 >99
Mine size (Number of employees)

Figure 3.—Number of underground nonlongwall bituminous coal mines by mine size and seam
height, 1994,


0.06

0.08

fies per 200,000 hours
8

£
i
rr

0.01

Th Low seams

Medium seams:

DD High seams

— Overall rate
within mine size

<20 20-49

50-

Mine size (Number of employees)

Figure 30.—Rate of fatal injuries from falls of supported roof by mine size and seam height, 1989-95.

0.06.

0.08:

Fatalities per 200,000 hours

0.01

1989-95,

TE bow scams
Medium seams

1 High seams

— Overall rate
within mine size

|

ST

<20 20-49

Mine size (Number of employees)
Figure 31.—Rate of fatal injuries from falls of unsupported roof by mine size and seam height,

Falls of Rib

low frequencies of injuries related to rib falls, this increasing
trend is evident overall as well as within two of the four mine

Because the amount of exposed rib increases as mining size categories (see table 23 and figure 32). Although injury
height increases, the expectation is that injury rates for falls of rates in low and medium seams within the smallest mine size
rib will increase as seam height increases. Despite the relatively _are the same, the highest rate occurs within high seams.


3.0

Hh Low seams
2s Medium seams
7 High seams
2 Overall rate
3 20 L|
2
8 —
3
8 —
8 15 - +|
o
a
8
‘5 10+] H
= J
os =
00+ r

<20 20-4 80-8 >99
Mine size (Number of employees)

Figure 27.—Rate of nonfatal disabling injuries from slips or falls by mine size and seam height,

1990-94.
Nonfatal Disabling Injuries Resulting increase from medium to high seams (see table 19 and figure
From Falls of Roof 28). Although this increasing trend is observed for only the

smallest and largest mines, injury rates in low seams are
Overall nonfatal disabling injury rates due to falls of roof consistently Jower than rates in high seams within all mine
increase as seam height increases, with a noticeably larger sizes,

‘Table 19.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from falls of roof
by mine size and seam height, 1990-94

Mine size (No. of employees)

‘Seam height <20 20-49 50-99 399 ‘Overall
No. Rate No. Rate No. Rate" No. Rate" No. Rate
Tow 107 —«86. 243 ~~ 71 88 52.55 473—86
Medium ........... ceeeees 69 1.08 189091 150.95 17075 57888
High 284.17 1331.23 75.90 3991.17 6351.14

Overall 204.96 6561.00 296.92, 621.94



EFFECTS OF MINING HEIGHT ON INJURY RATES IN U.S. UNDERGROUND
NONLONGWALL BITUMINOUS COAL MINES

By Barbara Fotta' and Launa G. Mallett, Ph.D.”

ABSTRACT

This report examines the effects of mining height on injury rates in U.S. underground nonlongwall
bituminous coal mines, controlling for both the employment size of the mine and the mining methods. Using
the mine-level employment and injury data reported to the Mine Safety and Health Administration, mines were
stratified by average coal seam height (<43 in, 43-60 in, and >60 in) and by the average number of employees
working at the mine (<20 employees, 20-49 employees, 50-99 employees, and >99 employees). To reduce
the confounding effects of mining method on injury rates, mines using longwall mining methods were
identified and excluded from analysis. The employment data show that as the mine size increases, the
proportion of hours worked in low seams decreases substantially. Additionally, miners injured in small, low-
seam mines are, on average, younger and less experienced than those injured in large high-seam mines.
Nonfatal disabling and fatal injury rates were computed within each category of employment size and seam
height for the major types of accidents (ground falls, powered haulage equipment, machinery, handling
materials, slips and falls, and hand tools). Our findings suggest that, regardless of the employment size, as
mining height increases, miners are at increasingly higher risk of injury from accidents due to slips or falls and
accidents involving shuttle cars and falls of ground. As mining height decreases, miners are at higher risk of
injury from accidents involving roof bolting machines, load-haul-dump types of powered haulage equipment,
personnel carriers, and powered haulage conveyors. On the other hand, regardless of the height of the coal
seam, miners working in large underground mines had higher rates of injuries resulting from accidents
involving handling materials and nonpowered hand tools, but lower rates of injury from accidents involving
continuous mining machines and lower rates of fatal injuries from falls of supported and unsupported mine
roof. Finally, miners working at small mines in low or medium seams are at higher risk of being fatally injured
by a fall of unsupported mine roof. These findings suggest the importance of considering the working height
of the mine, as well as the employment size of the mining operation, when developing intervention strategies
to reduce injury risk to underground coal miners. Results also identify the need to further explore how mining
height contributes to the frequency and severity of injuries.

"Research methodologist.
*Research sociologist.
Pittsburgh Research Laboratory, National Institute for Occupational Safety and Health, Pittsburgh, PA.


UNIT OF MEASURE ABBREVIATIONS USED IN THIS REPORT
ft foot (feet) in inch(es)

hr hour(s) % percent

Mention of any company name or product does not constitute endorsement by the National Institute for Occupational Safety
and Health.

To receive additional information about mining issues or other occupational safety and health problems, call 1-800-35-NIOSH
(1-800-356-4674), or visit the NIOSH Home Page on the World Wide Web at http://www.cdc.gov/niosh/homepage.html


Table 4.—Number and rate (per 200,000 hr) of nonfatal disabling back injuries from handling materials
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)
50-99

‘Seam height 20 20-49 399 ‘Overall
No. Rate No. Rate No. Rate" No. Rate No. Rate
210 1.68 485-4194 ~—«226~=«2.B0 SCOTS «1,218 2.22
1442.26 498 240 © 4502.84 5082.64 1,688 2.58
: 492.05 2302.43 1692.03 8812.59 1,329 2.39
Overall. 4031.90 7.213 2.15 8452.62 1,774 2.69
35:
Hh tow seams
30 RQ Medium seams
1 High seams
? os. NY — Overall rate
3 within mine size
2
2
8 20 Nz J ~
8
8
Bis.
g
2
3
Ero
os:
00+ r
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 15.—Rate of nonfatal disabling back injuries from handling materials accidents by mine size and

‘seam height, 1990-94.

the operation of some type of machinery, usually a roof bolting
machine (for 88% of these injuries) or a continuous miner (8%
of the injuries). However, when these types of incidents result
in a fatal injury, the accident is classified as a ground fall
accident, not a machinery accident. For consistency, nonfatal
disabling injuries resulting from these types of machinery-
related ground fall accidents will be excluded from the
machinery analysis and analyzed separately under accidents
involving falls of the mine roof or rib.

Of the remaining machinery-related incidents, 69% involved
roof bolting machines, 15% involved continuous miners, and
16% involved some other type of machinery, any one of which
provided too few numbers for meaningful analysis. The
nonfatal disabling and fatal injuries resulting from machinery
accidents involving roof bolting machines and continuous
miners are examined separately below.

Roof Bolting Machinery Accidents

Nonfatal disabling injury rates related to roof bolting
machines decrease overall as seam height increases (see table 5
and figure 16). For all except the largest mine size, injury rates
in low and medium seams are substantially higher than those
observed in high seams. Rates for the largest mines are the
lowest overall (.81) and show less variability across seam height
than rates for the smaller mine sizes. Consistent with the
distribution observed for nonfatal disabling injury rates, fatal
injury rates are substantially lower overall in high seams than in
low- or medium-seam heights (see table 6 and figure 17). Of
the 11 fatal injuries involving roof bolting machines, 10 oc-
curred in low or medium mining heights. Mines operating at
those heights accounted for 91% of the fatalities, but only 69%
of the employee hours.


MINE POPULATI

For the 7-year period from 1989 to 1995, 2,699 U.S.
underground nonlongwall bituminous coal mines with valid
seam heights were identified in the employment database. For
the 5-year period from 1990 to 1994, 2,288 mines were
identified. From 1989 to 1995, 51% of the mines included in
the analysis reported underground employee hours for at least
3 of the 7 years. For the 5-year period from 1990 to 1995, 56%
of the mines reported hours for at least 3 years. Eleven percent
and 22% of the mines reported hours annually throughout the
7- and 5-year periods, respectively. The distributions of
underground employee hours by mine size and seam height are
presented in figures 1 and 2 for the years 1989-95 and 1990-94,
respectively. Included in these figures are the percentage of
hours worked in low, medium, and high coal within each
category of mine size. Both figures illustrate that as mine size
increases, the proportion of hours worked in low coal decreases.
substantially. Additionally, these proportions remained
relatively constant across the two time periods.

From 1989 to 1994, the number of active nonlongwall
bituminous underground coal mines decreased by 32%, with a
corresponding 27% decrease in underground employee hours
and an 11% increase in coal production. The proportion of
mines operating in low, medium, or high coal seam heights has
remained relatively constant over the past 10 years. The
distribution of these mines in 1994 (the most recent year for
which MSHA data are complete) by seam height and mine size
is presented in figure 3. Both the number and percentage of
mines operating in low-coal seams decrease substantially as the
size of the mine increases. Virtually all low-coal mines are

100.

ION DESCRIPTION

located in the Appalachian coal basin, principally in Kentucky,
West Virginia, Virginia, and Pennsylvania (see figure 4).

Although continuous mining is the most prevalent method
used in underground coal, some smaller mining operations may
use conventional mining methods. The employment and injury
databases do not provide enough information to identify all of
the mines employing conventional mining methods or all of the
exposure hours and injuries associated with this method of
mining. However, included in the injury database is a field
identifying the underground mining method being employed at
the time of injury. For the 22,607 nonfatal disabling injuries
included in the present study for the period 1990-94, the
underground mining method was coded as continuous for
72.9%, conventional for 4.6%, unknown for 21.5%, and other
for 1% of the injuries. For each category of seam height and
mine size, the percentage of nonfatal disabling injuries within
that category for which the underground mining method was
coded as conventional mining is presented in figure 5. The two
highest percentages of conventional mining-related injuries are
reflected in mines with fewer than 50 employees operating in
Jow-coal seams. Additionally, nearly 10% of the nonfatal
disabling injuries that occurred in mines with more than 99
employees operating in medium seams were associated with
conventional mining methods. These implied differences in
exposure to conventional versus continuous mining methods
must be considered when examining differences in injury rates,
particularly for those injuries involving continuous mining
machines.

51%
Low
seams

80 Hy | gy Medium
seame
44% High
36% O seams
E L
cae
ra
FA 50%
2
® 40 |
g 50%
2 19%
E 14%)
ui 25% 2
20 Hy
11%
° T
<20 20-49 50-99 >99

Mine size (Number of employees)

Figure 1.—Number and percent (within mine size) of underground emplyee hours by mine size
and seam height for nonlongwalll bituminous coal mines, 1989-95.


HE bow seams
KX) Medium seams
[7 High seams
cots}

2 — Overall rate

3 within mine size

2

°

8

2

3

8

& 0010+

s —

a

2

&

g \

©

© o.005:

TM a

<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 22.—Rate of fatal injuries from shuttle car haulage accidents by mine size and seam height,

1989-95.
Load-Haul-Dump Equipment Personnel Carriers
Nonfatal disabling injury rates related to the use of load- Nonfatal disabling injury rates involving personnel carriers

haul-dump types of powered haulage equipment decrease as decrease overall as seam height increases (see table 13 and
seam height increases both overall as well as within each mine figure 24). This trend is particularly evident within the two
size category (see table 11 and figure 23). The five fatal smaller mine sizes. The four fatal injuries involving personnel
injuries associated with load-haul-dump types of powered carriers are too few in number and widely scattered for
haulage are too few in number and widely scattered for meaningful analysis (see table 14).

meaningful analysis (see table 12).

Table 11.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from load-haul-dump haulage
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)

‘Seam height <20 20-49 50-99 >99 ‘Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
Tow... 1291.03 216 «O87 39 (AB 32.84 TGSSCTG
Medium 35055 9043 63.40 6 295389.
High ... 625 32.30 26 3t 96.28 160__.29
Overall 170.80 338.60 728.40 79329



(MOSH

IC 9447 INFORMATION CIRCULAR/1997

Effects of Mining Height on Injury Rates
in U.S. Underground Nonlongwall
Bituminous Coal Mines

gs ORC,

U.S, DEPARTMENT OF HEALTH AND HUMAN SERVICES
C Public Health Service

Centers for Disease Control and Prevention
te N National Institute for Occupational Safety and Health
venvana

CENTERS FOR DISEASE CONTROL,
"AND PREVENTION


DEMOGRAPHICS OF INJURED MINERS

Previous studies have suggested that miners working in large
underground mines (>50 employees) are older and more
experienced than those working in smaller mines [Peters and
Fotta 1994b]. Although the age and experience of injured
miners may not be representative of the mining population as a
whole, differences among groups of injured miners may reflect
differences in the population as well. The MSHA injury/
accident database contains fields for recording the age, years of
total mining experience, years of experience at current mining
operation, and years of experience in current job classification
of the injured miner. The distributions of the median number
of years by seam height and mine size for miners injured in
1994 are presented for each of these four variables in figures 6
through 9, respectively. Note that within each category of mine

size, the lowest median number of years for both age and total
mining experience occurs in low seams. Note also that the
largest mines display the overall highest medians for age, years
of total mining experience, and years of experience at current
mine. The substantially higher medians observed at the largest
mines for the years of experience at current mine reflect, in part,
the longevity of larger underground mines. The distribution of
the median years of experience in current job classification
shows no consistent relation to either mine size or seam height.

In general, these statistics suggest that miners working in
small, low- seam mines are younger and have less overall
mining experience and less experience working in the mine
where they are currently employed than those working in large,
high-seam mines.

45
42_ 42
4 22 40 Low
40. 3838 r] seams
x 36 N’ 36 Medi
ium
as} 365 - |—34 Ly | SS seams
High
Bao || | Cl sess
5
& N= 3,583
£25 +
3
L204 ~ 4
< 20
s
3
15 H
10+ =
5+ LI
04
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 6.—Distribution by mine size and seam height of the median age of miners injured in 1994.


[242

Kentucky 151
|_}+s
132
West Virginia 421
ie4
86
Virginia 65
|__ke
23 | Low seams
Pennsylvania 24 KJ Medium seams
4 " oO High seams,
27
All other States 14
37
0) 50 100 150 200 250

Number of mines
Figure 4.—Number of underground nonlongwall bituminous coal mines by seam height and State,
1994.

25
ee
seams
19.4 Medium
20 IN seams
(Biss

seams
2
@
2"
£ 128
ral
°o
€
8 10-4 Q7
&

77
7A
65
54 45
34
27
24
1
0.3
oF T T —
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 5.—Percentage of conventional mining-related injuries within each combination of seam
height and mine size, 1990-94.


Table 20.—Number and rate (per 200,000 hr) of fatal injuries from falls of root
by mine size and seam height, 1989-95

Mine size (No. of employees)

Seam height =20 20-49 50-99 399 ‘Overall
No. Rate No. Rate No. Rate No. Rate "No. Rate
Tow. 17 «097 12 035 0 = 1.008 30.35
Medium 7 079 16.057 7 031 3.009 33015
High 2.059 4.027 6.054 5 .ott 7
Overall_. 26.087 32.041 13.029 9070
0.10-
EE bow seams
009+ oon
Medium seams
0.08 LO High seams
2 — Overall rate
3 007+ within mine size
2
3
SB 008+ —
Ss
Ss
N 0.05 7
o
a
D 0.04
03+
0.024
0.014 HY |
0.004 T T T
<20 20-49 0-99 >99

Mine size (Number of employees)
Figure 29.—Rate of fatal injuries from falls of roof by mine size and seam height, 1989-95.

Table 21.—Number and rate (per 200,000 hr) of fatal injuries from falls of supported roof
by mine size and seam height, 1989-95

Mine size (No, of employees)

Seam height <20 20-49 50-99 299 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
8 045 5 015 0 = 1.008 14 «018
3 034 13 046 7 .031 2 .006 25 027
2 059 3 020 3.026 3.006 41.014
413 044 21 027. 410 .022 6 006

Table 22.—Number and rate (per 200,000 hr) of fatal injuries from falls of unsupported roof
by mine size and seam height, 1989-95

Mine size (No. of employees)

Seam height <20 20-49 50-99 299 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
9.051 7 020 0 = 0 = 16 02t
4 045 3 011 07 - 1 .003 8 009
} = 1 .007 3.026 2.004 6.008
43.044 i 014 3.007, 3.003



HE low seams
12. — Medium seams
7 High seams

2 10 \) - |_}| __ Overall rate
g I within mine size
£ =
2°
8 04 +
o
S
a N
8 oe |__ H
2
2
=
=
Eos — L|

02 1

00 t t

<20 20-49 50-99 >99

Mine size (Number of employees)

Figure 28.—Rate of nonfatal disabling injuries from falls of roof by mine size and seam height,

1990-94,

Fatal Injuries Resulting From Falls of Roof

In contrast to the trends observed for nonfatal disabling
injury rates, the rates of fatalities due to falls of the mine roof
show more variation across mine size than across seam height
(see table 20 and figure 29). As mine size increases, the overall
fatality rate sharply decreases, Although these rates decline
overall as seam height increases, this trend, which is the reverse
of that observed for nonfatal disabling roof fall injuries, persists
only within the smallest mine size. Conversely, within the two
largest mine size categories, fatality rates increase with in-
creasing seam height, which is consistent with trends observed
for nonfatal disabling injuries.

Roof fall fatalities can be further differentiated as to whether
the victim was standing under supported or unsupported roof at
the time. A previous study reported higher fatality rates in low
seams than in high seams for falls of roof in which the victim
was positioned inby permanent roof supports [Peters and Fotta
1994a]. Using fatality investigation reports, a determination
was made as to whether the victim was positioned under

supported roof or unsupported roof. Of the 80 roof fall
fatalities, 50 were due to falls of supported roof; the remaining
30 were due to falls of unsupported roof. The distribution
across seam height and mine size of the numbers and rates of
these fatalities is presented in tables 21 and 22, respectively.

The rate of fatalities due to falls of supported roof declines
overall as mine size increases (see figure 30). The overall rate
for the smallest mines is about seven times that for the largest
mines. Variations in these rates show no obvious relation to
variations in seam height.

Fatality rates associated with falls of unsupported roof
decline overall as seam height increases (see table 22 and figure
31). However, this decreasing trend is observed only for the
two smaller mine sizes. The decline related to mine size is a
particularly strong trend, with rates decreasing by at least one-
half with each subsequent increase in mine size. The two
highest rates are observed for the smallest mines operating in
the low and medium seam heights. In fact, these mines ac-
counted for 43% (13 out of 30) of unsupported roof fall
fatalities, but only 11% of underground employee hours.


INTRODUCTION

This report examines the relationships between injury rates
and mining height in the U.S. underground nonlongwall
bituminous coal industry. Mining height is usually equal to the
height of the coal seam and can vary from as low as 20 in to a
height of 12 ft or more. Mining height affects not only mining
method and equipment choices, but also the posture, mobility,
and vision of the worker. The relationship between mining
height and the frequency and severity of injuries is confounded
by the effects of both mine size and mining method. Mines
operating in thinner scams of coal (less than 42 in high) tend to
have fewer employees and are more likely to use conventional
or continuous mining versus longwall mining methods, Two
previous studies [Hudson c.1977; National Academy of
Sciences 1983] that examined injury rates at different seam
heights were plagued by inadequate reporting of scam heights
to the Mine Safety and Health Administration (MSHA),

particularly by small mines. Although Hudson’s study
identified trends in injury rates across seam height for certain
types of accidents, the results were confounded by lack of
control for mine size and mining method. Although the
National Academy of Sciences study controlled for mine size,
it only examined overall fatality rates. In the present study, an
attempt is made to control for both mine size and mining
method. Incident rates for fatal and nonfatal disabling injuries
are examined separately by type of accident (using MSHA’s
accident classifications) and, when relevant, by the type of
equipment involved. Determining the extent to which seam
height, as opposed to other factors, affects fatal and nonfatal
injury rates at underground bituminous coal mines will increase
our understanding of how the underground mining environment
affects the risk of injury to miners.

METHODS AND DEFINITIONS

Data used in the present study are a subset of the data
collected annually by MSHA and recorded in its employment
and accident/injury databases for the U.S. coal industry.
Underground bituminous coal mines were identified and
categorized annually by their average seam height (reported in
inches) and their size (average annual number of employees).
Three categories of seam height were defined based on previous
definitions and the distribution of underground employee hours.
Low-seam heights are less than 43 in, medium-seam heights
range from 43 to 60 in, and high-seam heights exceed 60 in.
Mines with missing or unrealistic seam heights (c.g., seam
height of 1 in) were individually examined and corrections were
made based on valid seam heights for the mine from previous
and/or subsequent years, When such corrections could not be
made, the mines were excluded from all analyses. The
excluded mines accounted for less than 1% of underground
exposure hours.

Mine size is defined as the average annual number of
employees working at the underground mine (excluding office
and preparation plant workers). Four categories of mine size
were defined: <20 employees, 20-49 employees, 50-99 em-
ployees, and >99 employees. These distinctions were based on
previous definitions and the distribution of underground
exposure hours.

In the present study, nonfatal disabling injuries are defined
as those that resulted in a permanent disability and/or in days
away from work or days of restricted work activity. Nonfatal
disabling injury rates were computed for the 5-year period from
1990 to 1994. Fatal accident investigation reports were used to
obtain the actual mining height at the scene of the accident.
These mining heights, as opposed to the average coal seam
height of the mine, were used to categorize fatalities by seam
height. Given the low frequency of such events, fatal injury
rates were computed for the 7-year period from 1989 to 1995.5

To control for the effects of mining method on injury rates,
mines using the longwall mining method were identified and
excluded from analysis. Because only one longwall mine could
be identified as operating in low-seam heights, analyses across.
seam height were not conducted separately for these mines.
Annually, about 70 to 75 mines utilize longwall technology,
accounting for about one-third of the employee hours worked
in underground coal. Although many of these mines may also
use continuous mining methods in separate sections of the mine,
exposure hours for the different mining methods are not
available.

“Although MSHA data for 1995 are preliminary and nonfatal injuries and
employee hours may be underestimated, records of fatal injuries were complete


0.40:

0.384

0.30

2

id

0.15

ies per 200,000 hours

TM 0.104

0.054

0.00 T
<20 20-49

[Ey Low seams
Medium seams

[1 High seams

— Overall rate
within mine size

T
50-99 >99

Mine size (Number of employees)
Figure 18.—Rate of nonfatal disabling injuries from continuous miner machinery accidents by mine

size and seam height, 1990-94.

Table 8.—Number and rate (per 200,000 hr) of fatal injuries from continuous miner machinery

accidents by mine size and seam height, 1989-95

Mine size (No. of employees)

. Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No, Rate No. Rate No. Rate
Low... 2 011 1 .003 [i - 0 - 3 .004
Medium 1 011 2 .007 2 .009 1 .003 6 .006
High .. oO = 3 020 1 009 2.004 6 .008
Overall 3 010 6 .008. 3 007. 3 003



0:

HE Low seams
Medium seams
04: (1 High seams
2 — Overall rate
2 within mine size
2
Sos
Ss
3
8
a
a
@ 02
gQ
5
£
014
0.0 r

20-49

50-

99 > 99

Mine size (Number of employees)

Figure 25.—Rate of nonfatal disabling injuries from powered haulage conveyor accidents by mine size

and seam height, 1990-94.

Table 16.—Number and rate (per 200,000 hr) of fatal injuries from powered haulage conveyor
accidents by mine size and seam height, 1989-95

Mine size (No. of employees)

Seam height 20 20-49 50-99 399. ‘Overall
No. Rate No. Rate No. Rate No. Rate" No. Rate
Tow .. 0 = 0 = 0 = 0 = 0 =
Medium . 1 001 1 004 ) - 0 - 2 002
High . o = 2.013 oO 1__.002 3.004
Overall 1003, 3.004 o = 1.001

Locomotives

Although the types of powered haulage accidents
classified by machine type as locomotive, rail-mounted, or
lorry car accounted for only 4% of the nonfatal disabling
powered haulage injuries, they accounted for 9% (3 out of
32) of the fatal injuries. Most of the nonfatal disabling
injuries (84%) occurred in mines with 50 or more employees
(sce table 17 and figure 26) and all 3 fatalities occurred in
mines with more than 99 employees, | in each seam height

category. These differences related to mine size reflect the
fact that larger mines are most likely to employ this type of
powered haulage. Although overall nonfatal disabling injury
rates increase with increasing seam height (see table 16), this
trend is not evident within any mine size category. However,
all nonfatal disabling injury rates for mines with 50 or more
employees are higher than any of the rates for the smaller
mines. Both fatal and nonfatal injury trends reflect that these
types of powered haulage are predominantly used by larger
mining operations.

Table 17.Number and rate (per 200,000 hr) of nonfatal disabling injuries from locomotive
accidents by mine size and seam height, 1990-94

Mine size (No. of employees)

‘Seam height <20 20-49 50-99 399 ‘Overall

No. Rate No. Rate No. Rate "No. _Rate___No. Rate
Low 6 05 3 Ot 1 4 1 12 31 06
Medium 3 05 7 03 15.09 24 4908
High .. 0 00 2 02 5 06 4 12 48.09
Overall 9 04 12 02, 31.10 7612



12.
13.
14.
15.

17.
18.

19.
20.

21.
22.
23.

24,
25.

26.
27.
28.
29.
30.
31.
32.
33.

34.

ILLUSTRATIONS—Continued

Nonfatal disabling injuries by MSHA accident classification, 1990-94
Fatal injuries by MSHA accident classification, 1989-95,
Rate of nonfatal disabling injuries from handling materials accidents by mine size and seam height, 1990-94
Rate of nonfatal disabling back injuries from handling materials accidents by mine size and seam height,
1990-94 ..
Rate of nonfatal
1990-94 . . . :
Rate of fatal injuries from roof bolting machinery accidents by mine size and seam height, 1989-95 .
Rate of nonfatal disabling injuries from continuous miner machinery accidents by mine size and seam height,
1990-94 Loc nn eee Erne e EE Eee eee beeen ene ee
Rate of fatal injuries from continuous miner machinery accidents by mine size and seam height, 1989-95...
Nonfatal disabling injuries (1990-94) and fatal injuries (1989-95) by type of equipment involved in powered
haulage accidents
Rate of nonfatal disabling injuries from shuttle car haulage accidents by mine size and seam height, 1990-94
Rate of fatal injuries from shuttle car haulage accidents by mine size and seam height, 1989-95 ...........
Rate of nonfatal disabling injuries from load-haul-dump haulage accidents by mine size and seam height,
1990-94 ..
Rate of nonfatal disabling injuries from personnel carrier haulage accidents by mine size and seam height,
1990-94
Rate of nonfatal disabling injuries from powered haulage conveyor accidents by mine size and seam height,
1990-94 : : .
Rate of nonfatal disabling injuries from locomotive accidents by mine size and seam height, 1990-94
Rate of nonfatal disabling injuries from slips or falls by mine size and seam height, 1990-94.
Rate of nonfatal disabling injuries from falls of roof by mine size and seam height, 1990-94 . .
Rate of fatal injuries from falls of roof by mine size and seam height, 1989-95
Rate of fatal injuries from falls of supported roof by mine size and seam height, 1989-95
Rate of fatal injuries from falls of unsupported roof by mine size and seam height, 1989-95
Rate of nonfatal disabling injuries from falls of rib by mine size and seam height, 1990-94 .
Rate of nonfatal disabling injuries from machinery-related falls of ground by mine size and seam height,
1990-94

sabling injoies from roof bolting machinery accidents by mine size and seam height,

1990-94

TABLES

Number and rate (per 200,000 hr) of nonfatal disabling injuries for miners walking/running at time of injury
by mine size and seam height, 1990-94
Number and rate (per 200,000 hr) of nonfatal disabling injuries for miners crawling/kneeling at time of injury
by mine size and seam height, 1990-94 ,
Number and rate (per 200,000 hr) of nonfatal disabling injuries from handling materials accidents by mine
sizeand seam height, 1990-94 .
Number and rate (per 200,000 hr) of nonfatal disabling back injuries from handling materials accidents by
mine size and seam height, 1990-94... 00... 0cc0ececceeeeceeeeseeeeeeeeete este teeenenenees
Number and rate (per 200,000 hr) of nonfatal disabling injuries from roof bolting machinery accidents by
mine size and seam height, 1990-94
Number and rate (per 200,000 hr) of fatal injuries from roof bolting machinery accidents by mine size and
seam height, 1989-95 0.20.00. 0c0ccceceeeeeceeeeeeeeeseteee ester eenesetter sete eeeenerees
Number and rate (per 200,000 hr) of nonfatal disabling injuries from continuous miner machinery accidents
by mine size and seam height, 1990-94 00.0... .cccccceeeeeeeeeeeeecteeeeeseueeeeeeteeeeeees
Number and rate (per 200,000 hr) of fatal injuries from continuous miner machinery accidents by mine size
and seam height, 1989-95
Number and rate (per 200,000 hr) of nonfatal disabling injuries from shuttle car haulage accidents by mine
size and seam height, 1990-94 0... 0... cccceecveteeeceeeceeteeeeeeesettesteteetieeneeeeees

Page
uw

11
12

14
1S

16
7

17
18
19
20
21
22
23
24
25
26
27
27
28
29

30

12
13
14

15

16


Table 2—Number and rate (per 200,000 hr) of nonfatal disabling injuries for miners crawling/kneeling
at time of injury by mine size and seam height, 1990-94

Mine size (No. of employees)

Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
49 39 118 AT 24 .30 25 27 216 39
5 08 27 13 26 16 16 07 74 eal
i} 00 6 06 5 06 18 05 29 05
54 26 151 27 55. 17. 59 09
2
Low
seams
<] Medium
seams
15 ~ mr High
3 O seams
£ 1.25)
S
3 \
a 1.06)
=] 1 0.99 0.97 |_|
g
a
3 0.75 0.77
2
2 0.53| 0.56
05 \’ O41 |
0.34)
0.19
0 T T
<20 20-49 50-99 >99

Mine size (Number of employees)

Figure 10.—Rate (per 200,000 hr) of nonfatal disabling injuries for miners walking/running at time

of injury by mine size and seam height, 1990-94.

05
0.47
Low
seams
0.39 Medium

04 seams
2 High
g Om.
S 0.30
3 03
g 0.27
8
a
a
S02
z 0.16

0.13
O14
6.08 0.07
0.06 0.06 0.05
0.00
0. T T
<20 20-49 50-99 >99

Mine size (Number of employees)
Figure 11.—Rate (per 200,000 hr) of nonfatal disabling injuries for miners crawling/kneeling at
time of injury by mine size and seam height, 1990-94.


Handling materials (34%

Hand tools (7%)

Roof fall (7%)

Other (8%)

Machinery (18%)

“Slip or fall (11%)

Powered haulage (14%)

Figure 12.—Nonfatal disabling injuries by MSHA accident classification, 1990-94.

Roof fall (44%)
Other (6%)

Ignition/explosion
of gas or dust (7%)

180,

Electrical (9%)

Machinery (16%)

Powered haulage (18%)

Figure 13.—Fatal injuries by MSHA accident classification, 1989-95.


CONTENTS

Abstract .
Introduction .
Methods and definition:
Mine population description
Demographics of injured miners .
Reliability of seam height data .
Distribution of injuries by accident classification
Nonfatal disabling injuries.
Fatal injuries .
Results
Handling ‘materials accidents
Machinery accidents... .
Roof bolting machinery accidents
Continuous miner machinery accidents
Powered haulage accidents .
Shuttle cars
Load-haul-dump equipment.
Personnel carriers . .
Conveyors
Locomotives .
Slips and falls .
Falls of ground . .
Nonfatal disabling injuries resulting from falls of roof
Fatal injuries resulting from falls of roof
Falls of rib... 0.0.6.0... eee ee
Machinery-related falls of ground
Use of nonpowered hand tools .
Summary . .
Discussion
References

ILLUSTRATIONS

1, Number and percent (within mine size) of underground employee hours by mine size and seam height for
nonlongwall bituminous coal mines, 1989-95
2. Number and percent (within mine size) of underground employee hours by mine size and seam height for
nonlongwall bituminous coal mines, 1990-94 00... ...ccceseveeeeeseeeeeeeeeteecneeees
Number of underground nonlongwall bituminous coal mines by mine size and seam height, 1994
Number of underground nonlongwall bituminous coal mines by seam height and State, 1994...
5. Percentage of conventional mining-related injuries within each combination of seam height and mine size,
1990-94. :
Distribution by mine size and seam height of the median age of miners injured in 1994 . .
Distribution by mine size and seam height of the median years of total mining experience for miners
in 1994
8. Distribution by mine size and seam height of the mi
injured in 1994

9. Distribution by mine size and seam height of the median years of experience in current job classification for
miners injured in 1994.00.00... occ cece cece ee eee e cette eee e eee ee eee tee ene eee eneennes
10. Rate (per 200,000 hr) of nonfatal disabling injuries for miners walking/running at time of injury by mine size
and seam height, 1990-94 .........ccccceveceeeeeeeeeeeeeteueteueeteeeteeeceteceeeeeens

11. Rate (per 200,000 hr) of nonfatal disabling injuries for miners crawling/kneeling at time of injury by mine

size and seam height, 1990-94 ........0.ccceeeeeseueceeeeeeeeteeteueeeeeetneterenerens

ay

ns

ian years of experience at current mine for miners

rN

aun


REFERENCES

Gallagher S, Hamrick C, Comelius K, Redfern M [1995]. Peak LS/S1
moments associated with a cable hanging task (Abstract). In: Proceedings of the
Human Factors and Ergonomics Society 39th Annual Meeting, Vol. 2. Santa
Monica, CA: Human Factors and Ergonomics Society, p. 956.

Hudson $ (¢.1977]. Comparison of injury hazards in different coal seam
heights, MSHA Technical Report, Health and Safety Analysis Center, Denver,
0.

National Academy of Sciences (1983). Fatalities in small underground coal
mines. U.S. Bureau of Mines contract No. J0100145,

Peters R, Fotta B [1994a]. A review of recent data concerning accidents
‘caused by falls of unsupported roof. Holmes Safety Bulletin Dec:4-9.

Peters R, Fotta B [1994b]. Statistical profile of accidents at small
underground coal mines. In: Peters RH, comp. Improving Safety at Small
Underground Mines; Proceedings: Bureau of Mines Technology Transfer
Seminar. Pittsburgh, PA: U.S, Department of the Interior, Bureau of Mines, SP
18-94, pp. 5-14,


12

Ey Low seams
RQ) Medium seams

104

1 High seams

— Overall rate
within mine size

injuries per 200,000 hours
© °
os a

02+

0.04

<20

Mine size (Number of employees)

20-49

> 99

Figure 23.—Rate of nonfatal disabling injuries from load-haul-dump haulage accidents by mine size

and seam height, 1990-94,

Table 12.—Number and rate (per 200,000 hr) of fatal injuries from load-haul-dump haulage
accidents by mine size and seam height, 1990-94

Mine size (No, of employees)

Seam height <20 20-49 50-99 >99 Overall
No. Rate No. Rate No. Rate No. Rate No. Rate
[) - 1 .003 0 - Co) - 1 .001
1.004 1.004 0 - 0 - 2 002
High oO = ) = 1 009 1.002 2 003
Overall 4 003 2 003. 1 002 1 001
Table 13.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from personnel carrier haulage
accidents by mine size and seam height, 1990-94
Mine size (No. of employees)
Seam height =20 20-49 50-99 339 Overall
No. Rate No. Rate No. Rate No, Rate No. Rate
Low . 46 37 132 53 38 AT 30 32 246 AS
Medium 19 30 67 32 54 34 88 39 228 35
High. 313 716 3137134391853
Overall 68 32 216 38 123 38 252 38



Information Circular 9447

Effect of Mining Height on Injury Rates
in U.S. Underground Nonlongwall
Bituminous Coal Mines

By Barbara Fotta and Launa G. Mallett, Ph.D.

U.S. DEPARTMENT OF HEALTH AND HUMAN SERVICES
Public Health Service
Centers for Disease Control and Prevention
National Institute for Occupational Safety and Health
Pittsburgh Research Laboratory
Pittsburgh, PA

November 1997


‘Table 23.—Number and rate (per 200,000 hr) of

nonfatal disabling injuries from falls of rib

by mine size and seam height, 1990-94

Mine size (No. of employees)
50-99

Seam height 20 339 ‘Overall
No. Rate No. Rate No. Rate“ No. Rate No. Rate
iow 109 33 ~«S 13 16 2223 79.14
De 40.19 3628 BW 15 116.18
High 729 39.36 2935 75.22 150.27
Overall... 2a i 12.20 B24 131 20
0.40
EE tow seams
0.38 ~ §) Medium seams
1 Hon seams
2° — — Overall rate
g within mine size
S 05.
8
8
8 —
Ean N
a N
§ ous. 4
2
5
* 0.10 H
0.05 L|
0.00
«20 20-49 50-99 >99

Mine size (Number of employees)
Figure 32.—Rate of nonfatal disabling injuries from falls of rib by mine size and seam height,

1990-94,

Conversely, within the largest mine size, the highest rate is
observed in low seams. All three of the fatal injuries due to
falls of rib occurred in high seams for mines with 20-49
employees.

Machinery-Related Falls of Ground

As previously noted, machinery-related ground fall accidents
include both falls of the mine roof as well as falls of rib.
Although nonfatal disabling injury rates associated with these
accidents increase slightly overall as seam height increases, this

increasing trend persists only for the largest mines and mines
with 20-49 employees (see table 24 and figure 33).

USE OF NONPOWERED HAND TOOLS

Nonfatal disabling injury rates for accidents involving the
use of hand tools show no obvious trends related to seam height
(see table 25 and figure 34). Mines with fewer than 20
employees have the lowest rates of injury within every level of
seam height; the largest mines have the highest rates overall.


04.
TB Low seams
0.124 Medium seams
(1 High seams
2 010 |_|} —. Overall rate
3 within mine size
2
Se
8 os UW
s
s
&
3
& 006 H
9
3
2
2
= 008 +
0.02 H
0.00.

20-49

50-99

Mine size (Number of employees)

Figure 26.—Rate of nonfatal disabling injuries from locomotive accidents by mine size and seam height,

1990-94.
SLIPS AND FALLS

Injuries obtained when a miner either slips or falls are
expected to increase as seam height increases. Except for the
largest mines, nonfatal disabling injury rates related to the slip
or fall of a miner increases with increasing seam height both
overall as well as within each mine size category (see table 18
and figure 27), Note that the strength of this increasing trend
diminishes as mine size increases. A similar observation was
made in the preliminary analysis of nonfatal disabling injury
rates for miners injured while walking or running (refer to
figure 10).

FALLS OF GROUND

Ground fall accidents are classified separately as due
primarily to a fall of rock from either the mine roof or the mine

Table 18.—Number and rate (per 200,000 hr) of nonfatal disabling injuries from slips or fal

rib. When incidents classified as machinery-related ground fall
accidents are included with accidents classified directly as
ground falls, they total 3,521 and account for 15.6% of all
nonfatal disabling underground injuries. Machinery-related
ground fall accidents, discussed previously, account for 42.3%
of all ground fall accidents and include both falls of roof and
rib, Accidents attributed directly to falls of roof account for
another 47.9%; the remaining 9.8% are attributed directly to
falls of the mine rib. Fatal injuries classified as ground falls
accounted for 83 (46.1%) of the 180 fatal underground injuries
examined, Of these 83 fatalities, 80 were directly attributed to
falls of roof and 3 to falls of rib. Nonfatal disabling injury rates
will be examined separately for each of the three types of
ground fall accidents, and fatal injury rates will be examined for
falls of roof.

by mine size and seam height, 1990-94

ize (No. of employees)

Seam height =20 50-89 335 ‘Overall

No. Rate No. Rate No. Rate No. Rate
Tow... 61.49 76 04 176 1.87 461 —84
Medium . 51 80 1871.18 423° 1.87 861 1.31
High 42 1.76 1281.54 893 2.63. 1,240 2.23
Overall_. 15472 or 1.21 1.49: 6.



20

Low
seams

NX] Medium
seams

tian
seams

18
17
8 16.6
2 16 16
5 15 15 15 |_|
BT 137 14] 14
3 13
2 12
c=
£
=z 10+ i
2
o
2
o
oO
g
5% 7
nl
Oo
=
0+
<20 20-49 50-99 >99

Mine size (Number of employees)

N = 3,339

Figure 7.—Distribution by mine size and seam height of the median years of total mining experience

for miners injured in 1994.

10

9.2

Median years of experience at current mine

1204.1

Mine size (Number of employees)

20-49

50-99

>99

Low
Wn
High
om
N=3,581

Figure 8.—Distribution by mine size and seam height of the median years of experience at current
mine for miners injured in 1994.


Although the expected trends were evident within each mine
size category, the strength of the trends for both walking/
running and crawling/kneeling appears to weaken as mine size
increases. For example, within the smallest mine size, the rate
of injury to miners injured while walking/running in high seams
(.75) is almost four times the rate of injury observed in low
seams (.19). As mine size increases, this factor decreases such
that for the largest mines, the rate of injury to miners injured
while walking/running in high seams (1.76) is less than twice
the rate observed in low seams (1.06). A similar observation
can be made for the trends in injuries to miners whose activity
was classified as crawling/kneeling. These decreases in the
variability of injury rates for larger mining operations suggest
that the method of using average coal seam heights to

approximate actual working mining heights throughout a mine
may decrease in reliability as the size of the mining operation
increases. This is expected given that larger mining operations
are more extensive and therefore more likely to encounter
variations in coal seam thickness. Larger mines are also more
likely to be mining in multiple sections of the mine and, as
noted previously, the thickness of the coal seam can vary
within, as well as between, different sections of a mine.

Despite these variations, it appears that using three
categories of average coal seam heights to approximate actual
mining heights is a useful method for relating variations in
mining height to variations in the rate of injury to underground
miners.

DISTRIBUTION OF INJURIES BY ACCIDENT CLASSIFICATION

‘The analyses conducted for this report covered two separate
time periods. Nonfatal disabling injuries that occurred during
the 5-year period from 1990 to 1994 were the primary focus.
Findings from those analyses were then supplemented by a
review of fatal injuries during the 7-year period 1989 to 1995.
The additional years of data were required for the analyses
involving fatalities because of the small number of such events
in any one category. Regardless of how low the actual number
of fatalities is, however, the importance of the death of even one
worker cannot be overlooked. Additionally, the detailed
information obtained from fatal accident investigation reports
is rarely available for nonfatal injuries. Therefore, although
special care must be taken in the interpretation of such
relatively low-frequency events, such analyses may provide
additional insight.

NONFATAL DISABLING INJURIES

During the 5-year study period, 22,684 underground nonfatal
injuries resulting in lost time or days of restricted activity were

reported to MSHA by nonlongwall underground bituminous
coal mines, More than 99% of these injuries (22,607) had
corresponding seam height information reported by the mine
and were used in the analyses. Six major classifications of
accidents accounted for 91.6% of these injuries: (1) handling
materials, (2) machinery, (3) powered haulage, (4) slip or fall of
person, (5) fall of roof, and (6) nonpowered hand tools (see
figure 12).

FATAL INJURIES

During the 7-year period used for computing fatality rates,
180 miners were killed at underground nonlongwall
bituminous operations. The corresponding fatality rate was
.073 deaths per 200,000 underground employee hours. Three
types of accidents accounted for 78% of the deaths: (1) roof
falls, (2) powered haulage, and (3) machinery. Understanding
where these types of accidents are most likely to occur would
allow a more focused effort in reducing fatality rates (see fig-
ure 13).