by 

Feb. 28, 2011.

Potential of roof screening
� to reduce workers’ compensation costs
� by S.M. Moore, J. Pollard, S.K. Bhatt and C. Mark 

 S.M. Moore and C. Mark, members 

SME, and J. Pollard are biomedical 

engineer, mining engineer and 

biomedical engineer, respectively,
	

at the National Institute for 

Occupational Safety and Health,
	

Pittsburgh Research Laboratory,
	

Pittsburgh, PA. S.K. Bhatt is a 

consultant in Export, PA.
	

Abstract Each	year	more	than	400	coal	miners	are injured	(fatally	and	nonfatally)	by	rock	

falling	from	between	or	around	roof	supports.	Many	of	these	injuries	can	be	prevented	by	the	

installation	of	roof	screen.	However,	many	coal	mines	are reluctant	to	use	roof	screen	because	

of	the	added	cost.	The	goal	of	this	study	was	to	determine	the	potential	savings	in	workers’	

compensation	(WC)	premiums	that	can	be	achieved	due	to	a	reduction	in	rock	fall	injuries	after	

roof	screening.		The	WC	rate-setting	methods	utilized	by	Illinois	and	Kentucky	were	investigated	

in	this	study.	Using	data	obtained	from	the	Mine	Safety	and	Health	Administration,	national	and	 

state	WC	bodies	and	individual	insurance	companies	(e.g.,	average	cost	per	injury,	loss	cost	

rate, number	of	injuries	per	year,	number	of	injuries	preventable	each	year	with	roof	screening),	

baseline	mines	(representing	two	mine	sizes:	67	and	150	employees)	were	constructed	with	

realistic	ranges	for	estimates	of	injuries	and	WC	premium	costs.	Using	each	state’s	actual	WC	

rate-setting	formulas,	a	sensitivity	analysis	was	conducted	to	determine	the	total	savings	in	

WC	 costs	 after	 a	 three-year	 period.	Annual	 savings	 in	 WC	 premiums	ranged	 from	 $41,000	

to	$326,000	for	the	67-person	mine,	and	$96,000	to	$843,000	for	the	150-person	mine.	An	

economic	 analysis	 of	 the	 cost	 of	 a	 roof	 screening	 program	 at	 a	 67-person	 mine	 was	 also	

conducted.		The	annual	cost	of	a	roof	screening	program	here	was	estimated	at	$240,000.		At	

this	mine,	the	reduction	in	WC	premiums	alone	could	pay	for	the	entire	screening	program.

Introduction 

More than 400 roof fall injuries are 

reported to the U.S. Mine Safety and 

Health Administration (MSHA) each 

year. Nearly all of these injuries are 

caused by rocks falling between and 

around roof supports. Such rock falls 

also caused six fatal injuries between 

2006 and 2008. Technology is available to prevent the majority of these 

injuries and fatalities. Surface controls 

like straps, headers and large roof bolt 

plates can help, but the most effective prevention is roof screen (Fig. 1). 

Screen works best because it can cover 

up to 94% of the roof (Robertson et 

al., 2003). Screen also offers a first line 

of defense for roof bolter operators, by 

confining or deflecting small rocks that 

can come loose during drilling or bolt 

installation. 

Studies have shown that mines that 

use screen routinely have much lower 

rates of “struck by” rock fall injuries. 

Robertson et al. (2003) reported on two 

eastern longwall mines that reduced 

their rock fall injuries by more than 

80% after screening was introduced. A 

room-and-pillar mine in Indiana implemented a screening program, in which 

screen was installed in about half of 

the total drivage, typically in the belt 

and track entries, and in the intake and 

return escapeways (Compton et al., 

2007). The number of rock fall injuries 

that this mine reported to MSHA was 

reduced from an average of seven per 

year in the three years prior to screening to less than three per year in the five 

following years. 

Despite the fact that roof screening has obvious benefits to the safety 

of mine workers, some mining companies have yet to implement this safety 

measure due to concerns about the 

cost. However, injuries are also very 

expensive. According to information 

provided to the National Institute 

for Occupational Safety and Health 

(NIOSH) by the National Council on 

Compensation Insurance (NCCI), in 

the years 2002–2004, the average lost 

time workers’ compensation claim from 

a Kentucky underground coal mine 

cost $99,258. Medical inflation would 

have increased this loss to more than 

$130,000 in the years since (St. Louis 

Federal Reserve, 2010). While injury 

costs vary widely, the savings from preventing injuries may be so large that 

they can largely offset and, in some 

cases, even exceed, the direct costs of a 
roof screening program. 

In the U.S., the costs of injuries are covered by workers’ 

compensation (WC) insurance. Some coal companies, generally the larger ones, are self-insured and essentially bear 

the costs of injuries themselves. The others buy coverage 

from WC insurance providers. The goal of this study was to 

quantify the potential reduction in WC premiums that mining 

operations might expect after reducing the number of rock 

fall injuries with roof screening. These savings are then compared to the costs associated with a roof screening program 

at a typical room-and-pillar mine. 

Methods and results 

This study focused on WC premiums in Illinois and Kentucky. These states were selected because mines in the Illinois Basin have higher rock fall injury rates than mines in 

other coalfields (Molinda et al., 2008). Mines in these states 

may be highly interested in reducing WC costs through various methodologies, such as the one proposed in this study. 

WC rate-setting calculations for NCCI states. WC ratesetting functions may be performed by a state insurance fund 

or department of insurance. Some of these organizations 

designate these functions to rating bureaus or advisory organizations. The National Council on Compensation Insurance 

(NCCI) is the licensed rating organization in 36 states. Both 

Illinois and Kentucky are NCCI states.1 

 1Prior to 2008, Illinois mines used a different equation to arrive at the WC premium to be paid by each mine than they do today. 

However, since Illinois now employs the same equation as Kentucky, the currently used equation was implemented in both states for 

the purpose of this study. 

NCCI uses “experience rating” plans to modify premiums 

based on each individual employer’s past loss experience. 

Experience-rating plans, therefore, provide economic incentives to employers to reduce the frequency and severity of 

work-related injuries. The experience period is usually three 

full policy years, ending one year prior to the effective date 

of the modification. 

The NCCI formulas used to calculate the “experience 

rating modification” (MOD) are shown in Eqs. (1) and (2) 

(NCCI, 2003; printed with permission by NCCI). In Eq. (1), 

“Total A” reflects the individual employer’s actual loss experience, while in Eq. (2), “Total B” reflects its expected loss 

experience, based on the entire group of similar employers. 

Primary 

losses 

Stabilizing 

values 

Ratable 

excess 

Total 

APL + (1 - WV) × 

EEL + BV 

+ WV × 

AEL 

= Total A (1) 

EPL + (1 - WV) × 

EEL + BV 

+ WV × 

EEL 

= Total B (2) 

Where:
�

 APL = Actual primary losses
�

 WV = Weighting value
�

 EEL = Expected excess losses
�

 BV = Ballast value
�

 AEL = Actual excess losses
�

 EPL = Expected primary losses
�

The total expected losses are determined by multiplying the expected loss rate (ELR – obtained using a table 

provided by NCCI; use Classification 1016 for underground 

bituminous coal) by the payroll for the three years used in 

the rating. This value is then multiplied by 0.01 to put the 

number in terms per $100 of payroll. 

The primary losses are the ultimate losses with each injury at a mine up to the primary limiting factor ($5,000 per 

claim). The expected primary losses are then determined by 

multiplying the D-ratio (obtained using a table provided by 

NCCI; this ratio determines the portion of a mine’s expected 

losses that are expected to be primary losses) by the total 

expected losses (EL) (Eq. 3). Expected excess losses (EEL) 

are determined by subtracting the total expected primary 

losses (EPL) from the total expected losses (Eq. 4). 

EPL = (D ratio) × ELR × (3-year pay) × 0.01 (3) 

EEL = EL – EPL (4) 

Figure 1 

Roof screen provides superior protection from rock falls. 
The weighting value is obtained using a table from the 

NCCI Experience Rating Plan Manual and is based on the 

expected losses (note: different tables exist for different 

states). The weighting value determines how much of the 

actual losses and expected excess losses are used in the experience rating. The weighting value increases as expected 

losses increase. The ballast factor in the experience rating 

formula helps prevent the MOD from shifting too far above 

or below unity. It is added to both the actual primary losses 

and the expected primary losses. This value also increases as 

expected losses increase. 

Finally, the MOD is calculated by dividing Total A by 

Total B: 

MOD = Total A / Total B (5) 

An MOD that is less than unity implies that an employer 

has a better-than-average loss experience.2 

2

 In many states, WC premiums may also be modified by a schedule rating factor. The schedule rating factor, which may be positive or negative, 

reflects additional characteristics of the employer such as its use of “safety devices.” Details are reported in the NCCI Basic Manual, Appendix D, 

which can be obtained at www.ncci.com. 

Potential savings with roof screening. The rating period 

used for this study was 2001, 2002 and 2003, yielding WC 

costs for the year 2005. To demonstrate the expected amount 

of savings in WC premiums, baseline mines were created that 

are representative of mines that are experience-rated in Illinois and Kentucky. In each state, two baseline mines were 

used in the analysis, one with 67 employees and the other 

with 150 employees. 

To conduct the analysis, data for the following parameters 

had to be obtained: 

• payroll for 2001, 2002 and 2003; 

• total number of injuries for each of the three years; 

• number of injuries that would have been prevented 

by implementing roof screening for each of the three 

years; 

• base loss cost rate in 2005; 

• administrative fee multiplier applied by their 

insurance provider; and 

• the ultimate losses associated with each injury. 

In 2005, loss cost rate for Illinois was $33.13 (effective Jan. 

1, 2005), which included $9.67 and $6.99 for the state and federal black lung coverage, respectively, leaving $16.47 subject 

to a MOD factor (NCCI, 2009). For Kentucky, the loss cost 

rate was $31.02 (effective 9/1/04), whereby $1.18 and $5.06 

were for the state and federal black lung coverage, leaving 

$24.78 subject to a MOD factor (NCCI, 2009). 

Communications with NCCI and a large insurance provider in Kentucky (NCCI, 2009; Kentucky Employers, Mutual Insurance, 2009) yielded information regarding typical 

administrative multipliers used by insurers in Illinois and 

Kentucky. The multipliers used for Illinois and Kentucky 

were 1.46 and 1.115, respectively. To estimate the remaining 

parameters, several assumptions were made: 

• Payroll – The average mine worker salary in 2002 was 

determined to be $50,538 in Illinois and $47,473 in 

Kentucky (U.S. Bureau of the Census, 2002). These 

salaries were adjusted for inflation to estimate the 

salaries in 2001 and 2003.To determine the total payroll, the average salary was multiplied by the number 

of employees at the mine. 

• Total number of injuries – Table 1 summarizes the 

data provided to NIOSH by NCCI for experiencerated coal mines for the claim years 2002 – 2004. (For 

Illinois, the actual period covered was April 2001 

to March 2004. For Kentucky, the period was May 

2001 to April 2004). The average number of workers 

covered by NCCI plans during those years was estimated to be 1,003 in Illinois and 3,055 in Kentucky. 

Table 1 

Characteristics of WC claims, according to information provided to NIOSH by NCCI. Values are annual averages for the 

period 2002-2004.
	

Average annual 

payroll Estimated 

State ($ million) workers covered 

Illinois $51.2 1,003

Kentucky $143.6 3,055

Average annual WC claims per Average cost per 

WC claims worker per year WC claim
	

268 0.267 $29,577

869 0.284 $40,829

Table 2 

Characteristics of underground accidents from the MSHA database. Values are annual averages for 2002-2004.
	

Average Average Avg. days lost Avg. days lost 

annual annual Accidents per % Roof fall per roof fall per nonroof fall 

State workers accidents worker accidents accident accident 

Illinois 2,555 335 0.131 20.0% 29.6 39.2

Kentucky 8,542 1,002 0.117 17.1% 48.2 46.0
Dividing the reported number of claims by the estimated number of workers yields the average number 

of claims per worker. Using these data, the expected 

number of claims was then estimated to be 18 and 

19 for the 67-person mines in Illinois and Kentucky, 

respectively, and 40 and 43 for the 150-person mines 

in the two states. To accommodate mines that would 

be slightly above or below this average number of 

claims, the ranges used in the sensitivity analyses 

were 12-27 claims per year for the 67-person mine, 

and 27-60 claims per year for the 150-person mine. 

•	 Number of preventable injuries – NCCI does not 

report information on the causes of the injuries that 

result in WC claims. So the MSHA injury database 

was used to estimate the number of injuries that 

might have been prevented by roof screening. The 

MSHA data indicated that 17% of all Kentucky injuries, and 20% of all Illinois injuries, were the result of 

rock falls (Table 2). We assume these values to also 

be representative of the NCCI injury database. An 

analysis of the MSHA injury narratives determined 

that nearly all of these injuries could have been prevented by roof screen (Roberston et al., 2003). Table 

2 also shows that the severity of the rock fall injuries, 

expressed in terms of the average days lost per injury, 

was similar to that of other injuries that occurred 

underground. To accommodate mines that would 

be slightly above or below these expected preventable injuries, the sensitivity analyses assumed that 

the screening program reduced the number of WC 

claims at the baseline mines by 10%, 17% and 25%. 

•	 Ultimate losses per injury (actuarially determined 

amount; loss estimate at resolution of the claim 

based upon statistical trends for a specific state) – 

the incurred losses and claims data obtained from 

NCCI shown in Table 1 indicate that the average 

cost per claim (including both lost time and medical 

claims) was $29,577 in Illinois, while in Kentucky it 

was $40,829. 

•	 NCCI	equation	parameters: The expected loss ratio 

used for Illinois was 10.21 and the discount ratio was 

0.15. For Kentucky, these values were 12.9 and 0.17. 

The weighting value used for the 67-person mine was 

0.40 in Illinois and 0.56 in Kentucky, and the ballast 

values were 133,125 and 133,900, respectively. For 

the 150-person mine, the weighting values were 0.55 

in Illinois and 0.67 in Kentucky, and the ballast values were 260,925 and 285,693, respectively. Again, all 

of these values are determined using tables provided 

by NCCI for each state. 

The findings from the analysis are summarized in Figs. 

2 and 3. 

 

Figure 2
	

Potential cost savings from roof screening. The x axis is the potential reduction in WC insurance premiums and the y

axis is the estimated total losses avoided, due to the screening program. 

Depending on the total number of WC claims, the 

number of claims prevented by roof screening ranged between 1 and 7 for the 67-person mine, and between 3 and 15 

for the 150-person mine. Figure 2 shows that the cost savings 

(total losses avoided) for these prevented injuries ranged 

from $35,000 to $612,000. The potential reduction in WC 

premiums actually exceeded the cost savings by 37% for the 

larger mines and 19% for the smaller ones. In Illinois, po-
tential annual savings in WC premiums ranged from $41,000 

to $227,000 for the 67-person mine, and $96,000 to $612,000 

for the 150-person mine. In Kentucky, potential savings were 

$58,000 to $326,000 for the smaller mine, and $151,000 to 

$843,000 for the larger one. 

Figure 3 shows that, on average, a 10% reduction in the 

number of WC claims results in an average 6.2% reduction 

in the traumatic portion of the WC premium (the portion 

affected by the MOD, which does not include the state and 

federal Black Lung portions of the premium). The percent 

reduction in the premium varies substantially, however, with 

the highest value (of 7.7%) for the larger mines with the largest number of total WC claims. 

Figure 3 

Potential reduction in WC premiums (excluding Black Lung) due to roof screening. 

Economics of screening. An economic analysis was conducted in order to estimate what fraction of the costs associated with the implementation of roof screening would be 

offset by the reduction in WC premiums. The analysis was 

performed for a typical Midwestern room-and-pillar mine 

employing 67 people and producing 726 kt (800,000 st) per 

year. The mine was assumed to operate two shifts per day, 

using a single super section employing two continuous miners 

and two roof bolters. A critical assumption was that adding 

roof screen did not decrease the footage of advance per shift. 

This assumption is reasonable if best practices for screen installation, such as those described by Compton et al. (2007), 

are used, and particularly if only about 50% of the drivage is 

screened. Other assumptions were: 

• The section advances 122 m/shift (400 ft/shift) in a 

1.5-m- (5-ft)- thick coal seam. 

• Straps, costing $8 each, are currently installed in all 

headings and crosscuts. 

• Screen installation requires an additional 10 minutes per 12 m (40 ft) of advance (Note: This additional time for screening affects the time to install 

roof support materials, but does not affect the time 

for cutting coal (production time), because that is 

done by the continuous mining machine in a different heading). 

• Screen, costing $16 per piece, will replace the straps 

in 50% of the drivage. 

• Labor cost (fully loaded) is $40/hour. 

• Maintenance costs may be excluded, as they are not 

normally required for screening. 

• No additional injuries due to material handling. 

The incremental costs associated with the roof screening 

program can be calculated as follows: 

• Cost of screen = $6.56/ m ($2/ft). 

• Cost of labor to install screen = 0.82 min/m (0.25 

min/ft) with two roof bolter operators = $1.08/m 

($0.33/ft). 

• Cost of supplying screen to the section is approximately $0.33/m ($0.10/ft). 

The total cost for installing screen is, therefore, approximately $8/m ($2.43/ft) or $0.64/t ($0.58/st). If screen is installed in 50% of the drivage, the cost per ton for the mine 
drops to $0.32/t ($0.29/st). If this one-section mine produces 

726 kt (800,000 st) annually, the yearly cost for the screen 

installation in half of the drivage is approximately $240,000. 

The analysis summarized in Figs. 2 and 3 showed that the 

potential WC premium savings after implementing a roof 

screening program could approach, or even exceed, these 

estimated costs for the screen installation. Moreover, it is important to consider that the WC expense is only a fraction of 

the total cost of “struck by” injuries. In addition, the mining 

operation will incur indirect administrative costs to replace 

injured workers, costs to train new replacement workers and 

production delays due to inexperienced workers on the continuous miner or roof bolter.A roof fall that causes an injury 

can also cause production delays, due to MSHA inspection 

of the fall area and plan/operational changes made to accommodate MSHA requirements to prevent further “struck by” 

accidents. “Struck by” injuries can have a negative effect on 

the morale of the entire underground work force and may 

make the miners question their own safety. There may also 

be legal costs linked to “struck by” injuries, such as fines or 

penalties related to reportable injuries, legal fees and possible “gross negligence” lawsuits. It should be noted that 

the costs discussed in this paper are from the employer’s 

perspective and not from a societal perspective, which would 

also include the costs associated with pain and suffering of 

the mine worker and the consequences this would place on 

their families. 

Roof screening also improves general ground control 

in the mine and can provide substantial economic benefits 

above and beyond those directly related to injury prevention by: 

• Reducing the need for spot bolting due to deteriorating roof conditions. 

• Minimizing production losses due to cleanup and resupport of important belt, travel and escape entries. 

• Reducing major roof falls by providing confinement 

between bolts and preventing unraveling above bolt 

anchorage.

 Conclusions 

In this study, the methods utilized by Illinois and Kentucky to determine a mine’s WC premiums were detailed. A 

sensitivity analysis was conducted, in which the number of 

total injuries and the number of injuries that could have been 

prevented with roof screening were varied. The potential 

savings were substantial. It was found that the reduction in 

premiums actually exceeded the reduction in actual losses 

by 19-37%, depending on the size of the mine evaluated. In 

many cases, the potential savings approached or even exceeded the estimated costs of a screening program. Roof screen 

can also bring additional benefits to a company’s bottom 

line by improving ground control and reducing the sizable 

indirect costs of injuries. 

There were several limitations to the current study. The 

mines utilized in the study were hypothetical, as opposed to 

using real mine demographic and injury data. The total number of injuries and the preventable injuries at each hypothetical mine were based upon injury data obtained from NCCI 

and the MSHA injury database in each state. For each state, 

an average injury cost was used for every claim, rather than 

using a realistic distribution of claim costs. Finally, it should 

be noted that large coal companies tend to purchase nonstandard WC policies. Specifically, they often purchase some type 

of risk-sharing policy, such as a large deductible, or they may 

be self-insured and purchase an excess WC policy. For the 

latter case, the cost associated with every claim eliminated 

through roof screening is directly saved by the company. Additional savings would then be observed by the reduction in 

the MOD associated with the excess WC policy. 

Roof screen has the potential to prevent hundreds of 

injuries caused by the fall of small rocks between and around 

roof supports. Currently, these injuries occur while miners are 

located under “supported” roof. Many mines may be overestimating the costs of installing screen and underestimating 

the potential economic benefits from reducing the number 

of “struck by” injuries. It is hoped that this paper will help 

convince mining operations to give this valuable technology 

another look. 

Acknowledgments 

The authors thank Deno M. Pappas of NIOSH for assistance with the MSHA database on accident statistics and the 

National Council on Compensation Insurance, Rockwood 

Casualty Insurance Company, Kentucky Employers’ Mutual 

Insurance and Petroleum Casualty Company for providing 

useful information on compensation insurance. 

Disclosure 

The findings and conclusions in this report are those of 

the authors and do not necessarily represent the views of the 

National Institute for Occupational Safety and Health. 

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