This chapter is from the book
This chapter is from the book
This chapter is from the book
1-3 Accident and Loss Statistics
Accident and loss statistics are important measures of the effectiveness of safety programs. These statistics are valuable for determining whether a process is safe or whether a safety procedure is working effectively.
Many statistical methods are available to characterize accident and loss performance. These statistics must be used carefully. Like most statistics they are only averages and do not reflect the potential for single episodes involving substantial losses. Unfortunately, no single method is capable of measuring all required aspects. The three systems considered here are
- OSHA incidence rate,
- Fatal accident rate (FAR), and
- Fatality rate, or deaths per person per year
All three methods report the number of accidents and/or fatalities for a fixed number of workers during a specified period.
OSHA stands for the Occupational Safety and Health Administration of the United States government. OSHA is responsible for ensuring that workers are provided with a safe working environment. Table 1-2 contains several OSHA definitions applicable to accident statistics.
Table 1-2. Glossary of Terms Used by OSHA and Industry to Represent Work-Related Lossesa, b
|
Term |
Definition |
|
First aid |
Any one-time treatment and any follow-up visits for the purpose of observation of minor scratches, cuts, burns, splinters, and so forth that do not ordinarily require medical care. Such one-time treatment and follow-up visits for the purpose of observation are considered first aid even though provided by a physician or registered professional personnel. |
|
Incident rate |
Number of occupational injuries and/or illnesses or lost workdays per 100 full-time employees. |
|
Lost workdays |
Number of days (consecutive or not) after but not including the day of injury or illness during which the employee would have worked but could not do so, that is, during which the employee could not perform all or any part of his or her normal assignment during all or any part of the workday or shift because of the occupational injury or illness. |
|
Medical treatment |
Treatment administered by a physician or by registered professional personnel under the standing orders of a physician. Medical treatment does not include first aid treatment even though provided by a physician or registered professional personnel. |
|
Occupational injury |
Any injury such as a cut, sprain, or burn that results from a work accident or from a single instantaneous exposure in the work environment. |
|
Occupational illness |
Any abnormal condition or disorder, other than one resulting from an occupational injury, caused by exposure to environmental factors associated with employment. It includes acute and chronic illnesses or diseases that may be caused by inhalation, absorption, ingestion, or direct contact. |
|
Recordable cases |
Cases involving an occupational injury or occupational illness, including deaths. |
|
Recordable fatality cases |
Injuries that result in death, regardless of the time between the injury and death or the length of the illness. |
|
Recordable nonfatal cases without lost workdays |
Cases of occupational injury or illness that do not involve fatalities or lost workdays but do result in (1) transfer to another job or termination of employment or (2) medical treatment other than first aid or (3) diagnosis of occupational illness or (4) loss of consciousness or (5) restriction of work or motion. |
|
Recordable lost workday cases due to restricted duty |
Injuries that result in the injured person not being able to perform their regular duties but being able to perform duties consistent with their normal work. |
|
Recordable cases with days away from work |
Injuries that result in the injured person not being able to return to work on their next regular workday. |
|
Recordable medical cases |
Injuries that require treatment that must be administered by a physician or under the standing orders of a physician. The injured person is able to return to work and perform his or her regular duties. Medical injuries include cuts requiring stitches, second-degree burns (burns with blisters), broken bones, injury requiring prescription medication, and injury with loss of consciousness. |
The OSHA incidence rate is based on cases per 100 worker years. A worker year is assumed to contain 2000 hours (50 work weeks/year x 40 hours/week). The OSHA incidence rate is therefore based on 200,000 hours of worker exposure to a hazard. The OSHA incidence rate is calculated from the number of occupational injuries and illnesses and the total number of employee hours worked during the applicable period. The following equation is used:
Equation 1-1
An incidence rate can also be based on lost workdays instead of injuries and illnesses. For this case
Equation 1-2
The definition of a lost workday is given in Table 1-2.
The OSHA incidence rate provides information on all types of work-related injuries and illnesses, including fatalities. This provides a better representation of worker accidents than systems based on fatalities alone. For instance, a plant might experience many small accidents with resulting injuries but no fatalities. On the other hand, fatality data cannot be extracted from the OSHA incidence rate without additional information.
The FAR is used mostly by the British chemical industry. This statistic is used here because there are some useful and interesting FAR data available in the open literature. The FAR reports the number of fatalities based on 1000 employees working their entire lifetime. The employees are assumed to work a total of 50 years. Thus the FAR is based on 108 working hours. The resulting equation is
Equation 1-3
The last method considered is the fatality rate or deaths per person per year. This system is independent of the number of hours actually worked and reports only the number of fatalities expected per person per year. This approach is useful for performing calculations on the general population, where the number of exposed hours is poorly defined. The applicable equation is
Equation 1-4
Both the OSHA incidence rate and the FAR depend on the number of exposed hours. An employee working a ten-hour shift is at greater total risk than one working an eight-hour shift. A FAR can be converted to a fatality rate (or vice versa) if the number of exposed hours is known. The OSHA incidence rate cannot be readily converted to a FAR or fatality rate because it contains both injury and fatality information.
Example 1-1.
A process has a reported FAR of 2. If an employee works a standard 8-hr shift 300 days per year, compute the deaths per person per year.
Solution
|
Deaths per person per year |
= |
(8 hr/day) x (300 days/yr) x (2 deaths/108 hr) |
|
= |
4.8 x 10–5. |
Typical accident statistics for various industries are shown in Table 1-3. A FAR of 1.2 is reported in Table 1-3 for the chemical industry. Approximately half these deaths are due to ordinary industrial accidents (falling down stairs, being run over), the other half to chemical exposures.2
Table 1-3. Accident Statistics for Selected Industries
|
OSHA incident rates (U.S.) |
||||||
|
Recordablea |
Days Away from Worka |
FAR (UK)c |
||||
|
Industrial activity |
2007 |
2007 |
2000 |
2005 |
1974–78 |
1987–90 |
|
Agriculture1 |
6.1 |
3.2 |
24.1 |
27 |
7.4 |
3.7 |
|
Chemical and allied products |
3.3 |
1.9 |
2.5 |
2.8 |
2.4 |
1.2 |
|
Coal mining |
4.7 |
3.2 |
50 |
26.8 |
14.5 |
7.3 |
|
Construction |
5.4 |
2.8 |
10 |
11.1 |
10 |
5.0 |
|
Vehicle manufacturing |
9.3 |
5.0 |
1.3 |
1.7 |
1.2 |
0.6 |
|
All manufacturing |
5.6 |
3.0 |
3.3 |
2.4 |
2.3 |
1.2 |
The FAR figures show that if 1000 workers begin employment in the chemical industry, 2 of the workers will die as a result of their employment throughout all of their working lifetimes. One of these deaths will be due to direct chemical exposure. However, 20 of these same 1000 people will die as a result of nonindustrial accidents (mostly at home or on the road) and 370 will die from disease. Of those that perish from disease, 40 will die as a direct result of smoking. 3
Table 1-4 lists the FARs for various common activities. The table is divided into voluntary and involuntary risks. Based on these data, it appears that individuals are willing to take a substantially greater risk if it is voluntary. It is also evident that many common everyday activities are substantially more dangerous than working in a chemical plant.
Table 1-4. Fatality Statistics for Common Nonindustrial Activitiesa, b
|
Activity |
FAR (deaths/108 hours) |
Fatality rate (deaths per person per year) |
|
Voluntary activity |
||
|
Staying at home |
3 |
|
|
Traveling by |
||
|
Car |
57 |
17 x 10–5 |
|
Bicycle |
96 |
|
|
Air |
240 |
|
|
Motorcycle |
660 |
|
|
Canoeing |
1000 |
|
|
Rock climbing |
4000 |
4 x 10–5 |
|
Smoking (20 cigarettes/day) |
500 x 10–5 |
|
|
Involuntary activity |
||
|
Struck by meteorite |
6 x 10–11 |
|
|
Struck by lightning (U.K.) |
1 x 10–7 |
|
|
Fire (U.K.) |
150 x 10–7 |
|
|
Run over by vehicle |
600 x 10–7 |
For example, Table 1-4 indicates that canoeing is much more dangerous than traveling by motorcycle, despite general perceptions otherwise. This phenomenon is due to the number of exposed hours. Canoeing produces more fatalities per hour of activity than traveling by motorcycle. The total number of motorcycle fatalities is larger because more people travel by motorcycle than canoe.
Example 1-2.
If twice as many people used motorcycles for the same average amount of time each, what will happen to (a) the OSHA incidence rate, (b) the FAR, (c) the fatality rate, and (d) the total number of fatalities?
Solution
- The OSHA incidence rate will remain the same. The number of injuries and deaths will double, but the total number of hours exposed will double as well.
- The FAR will remain unchanged for the same reason as in part a.
- The fatality rate, or deaths per person per year, will double. The fatality rate does not depend on exposed hours.
- The total number of fatalities will double.
Example 1-3.
If all riders used their motorcycles twice as much, what will happen to (a) the OSHA incidence rate, (b) the FAR, (c) the fatality rate, and (d) the total number of fatalities?
Solution
- The OSHA incidence rate will remain the same. The same reasoning applies as for Example 1-2, part a.
- The FAR will remain unchanged for the same reason as in part a.
- The fatality rate will double. Twice as many fatalities will occur within this group.
- The number of fatalities will double.
Example 1-4.
A friend states that more rock climbers are killed traveling by automobile than are killed rock climbing. Is this statement supported by the accident statistics?
Solution
The data from Table 1-4 show that traveling by car (FAR = 57) is safer than rock climbing (FAR = 4000). Rock climbing produces many more fatalities per exposed hour than traveling by car. However, the rock climbers probably spend more time traveling by car than rock climbing. As a result, the statement might be correct but more data are required.
Recognizing that the chemical industry is safe, why is there so much concern about chemical plant safety? The concern has to do with the industry's potential for many deaths, as, for example, in the Bhopal, India, tragedy. Accident statistics do not include information on the total number of deaths from a single incident. Accident statistics can be somewhat misleading in this respect. For example, consider two separate chemical plants. Both plants have a probability of explosion and complete devastation once every 1000 years. The first plant employs a single operator. When the plant explodes, the operator is the sole fatality. The second plant employs 10 operators. When this plant explodes all 10 operators succumb. In both cases the FAR and OSHA incidence rate are the same; the second accident kills more people, but there are a correspondingly larger number of exposed hours. In both cases the risk taken by an individual operator is the same.4
It is human nature to perceive the accident with the greater loss of life as the greater tragedy. The potential for large loss of life gives the perception that the chemical industry is unsafe.
Loss data5 published for losses after 1966 and in 10-year increments indicate that the total number of losses, the total dollar amount lost, and the average amount lost per incident have steadily increased. The total loss figure has doubled every 10 years despite increased efforts by the chemical process industry to improve safety. The increases are mostly due to an expansion in the number of chemical plants, an increase in chemical plant size, and an increase in the use of more complicated and dangerous chemicals.
Property damage and loss of production must also be considered in loss prevention. These losses can be substantial. Accidents of this type are much more common than fatalities. This is demonstrated in the accident pyramid shown in Figure 1-3. The numbers provided are only approximate. The exact numbers vary by industry, location, and time. "No Damage" accidents are frequently called "near misses" and provide a good opportunity for companies to determine that a problem exists and to correct it before a more serious accident occurs. It is frequently said that "the cause of an accident is visible the day before it occurs." Inspections, safety reviews, and careful evaluation of near misses will identify hazardous conditions that can be corrected before real accidents occur.
)
Figure 1-3 The accident pyramid.
Safety is good business and, like most business situations, has an optimal level of activity beyond which there are diminishing returns. As shown by Kletz,6 if initial expenditures are made on safety, plants are prevented from blowing up and experienced workers are spared. This results in increased return because of reduced loss expenditures. If safety expenditures increase, then the return increases more, but it may not be as much as before and not as much as achieved by spending money elsewhere. If safety expenditures increase further, the price of the product increases and sales diminish. Indeed, people are spared from injury (good humanity), but the cost is decreased sales. Finally, even higher safety expenditures result in uncompetitive product pricing: The company will go out of business. Each company needs to determine an appropriate level for safety expenditures. This is part of risk management.
From a technical viewpoint, excessive expenditures for safety equipment to solve single safety problems may make the system unduly complex and consequently may cause new safety problems because of this complexity. This excessive expense could have a higher safety return if assigned to a different safety problem. Engineers need to also consider other alternatives when designing safety improvements.
It is also important to recognize the causes of accidental deaths, as shown in Table 1-5. Because most, if not all, company safety programs are directed toward preventing injuries to employees, the programs should include off-the-job safety, especially training to prevent accidents with motor vehicles.
Table 1-5. All Accidental Deathsa
|
Type of death |
1998 deaths |
2007 deaths |
||
|
Motor-vehicle |
||||
|
Public nonwork |
38,900 |
40,955 |
||
|
Work |
2,100 |
1,945 |
||
|
Home |
200 |
200 |
||
|
Subtotal |
41,200 (43.5%) |
43,100 (35.4%) |
||
|
Work |
||||
|
Non-motor-vehicle |
3,000 |
2,744 |
||
|
Motor-vehicle |
2,100 |
1,945 |
||
|
Subtotal |
5,100 (5.4%) |
4,689 (3.9%) |
||
|
Home |
||||
|
Non-motor-vehicle |
28,200 |
43,300 |
||
|
Motor-vehicle |
200 |
200 |
||
|
Subtotal |
28,400 (30.0%) |
43,500 (35.7%) |
||
|
Public |
20,000 (21.1%) |
30,500 (25%) |
||
|
All classes |
94,700 |
121,789 |
When organizations focus on the root causes of worker injuries, it is helpful to analyze the manner in which workplace fatalities occur (see Figure 1-4). Although the emphasis of this book is the prevention of chemical-related accidents, the data in Figure 1-4 show that safety programs need to include training to prevent injuries resulting from transportation, assaults, mechanical and chemical exposures, and fires and explosions.
)
Figure 1-4 The manner in which workplace fatalities occurred in 2006. The total number of workplace fatalities was 5840; this includes the above plus 14 for bodily reaction and exertion, and 10 nonclassified. Data source: , 2009, p. 56.