Chapter 2-Safety Analysis

A Statistical Approach

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Roles of Statistics in Safety

Although the myth is that Statistics are too hard for a regular person to understand, it is accutually quite the opposite. Statistics are relatively easy to understand. Statistical data serves a number of functions in safety.

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Statistics in Safety

Data is frequently used to determine problem areas.

Statistics can also be helpful in developing strategies in safety education.

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Statistics defined

Statistics has to do with the extraction of information from numerical data.There are two types of Statistics:

1. Descriptive Statistics

2. Inferential Statistics

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Two Types of Statistics

Descriptive Statistics Give information

about the characteristics of a particular group.

Example:Total deaths for

motor vehicle accidents.

Inferential Statistics Consists of

estimations, generalizations, or predictions about a particular group.

Example:A prediction of how

many people will be traveling this year on Thanksgiving.

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Presentation of Data

Frequency Distributions can make large numbers of scores easier to work with. It presents the numbers in an efficient manner.

Any set of Values are known as a distribution.

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Percentage as a Presentation of Data

Percentages are another form of presenting data.

They are derived by dividing the number of cases in interest by the total number of cases.

% of Deaths=Number of deaths in age group

Number of Total deaths

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Presentation of Data

Rates are percentages based on particular population. Unlike percentage, rates control for

population;rates are always based on the same figure;usually 100,000.

The specific death rate is the number of deaths that occur each year for every 100,00 persons in a certain population.

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Death Rate

A death rate would be found by using this equation:

Specific Death Rate= Number of deaths for a particular

population X’s100,000Specific Population

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Presentation of Data

Graphical Presentations enable the reader to take in information based on pictures or graphics. A graph can enable one to see the

“big picture” but not the raw data.

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Errors and Problems

The collection of accurate data is vital in the field of safety.There are two important aspects of data collection1. Validity-

How close does the data correspond to the situation?

2. Reliability- How closely do the observations match

each other?

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Finding Reliable Sources

The National Safety Council is one of the most reliable sources for nationwide data pertaining to accidents of all kinds. It was established in 1913, by an Act

of Congress, and has now become a non-profit, nongovernmental organization that has become the leader in safety services.

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Finding Reliable Sources

National Center for Health StatisticsNational Injury Information ClearinghouseNational Criminal Justice Reference Service(NCJRS)National Highway Traffic Safety Administration(NHTSA)

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National Highway Traffic Safety Administration

Since 1975, NHTSA has analyzed fatal motor vehicle crashes, which is known as Fatal Accident Reporting System(FARS). With this information, researchers have been able to come up with information that is valuable in determining the causes for a crash.

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The Key to Accurate Statistics

Valid and Reliable Safety Statistics depend on the individuals who provide the safety services.Writing the facts down accurately may be time consuming, but it is helpful in Statistical Data.

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Classification of Accidents

Most Safety Researchers classify accidents in four basic groups:

1. Motor Vehicle Accidents2. Work-related Accidents3. Home Accidents4. Public Accidents

Then the information is broken down further within the groups.

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Changes in the Accident Scene

1903-1989

Since 1903, The accident death rate has declined by 56%.Since 1979, the accident death rate has dropped 10%.

1903

1989

56%

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Modern Approaches to Accident Investigation

First, the four factors that involve safety during an activity as discussed in chapter one:

1. Understanding the Difficulty2. The Ability of the Performer3. Immediate Sate of the Performer4. Conditions of the Environment

These four components make up a system

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Modern Approaches to Accident Investigation

Accidents can be thought of as malfunctions in a system.An example would be the aerospace industry. Because of the highly sophisticated

equipment, the engineers had to come up with systems safety analysis.

They used this to predict when problems would occur so that they could be fixed before it happened. Now they are used in all industries.

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Modern Approaches to Accident Investigation

Failure Mode and Effect Analysis- Each component or

factor is evaluated on how it will affect the overall system if it fails. This is used to come up with plans for back-up components.

Fault-Tree Analysis- Accident prevention

model that reasons backwards from an event that is unwanted. It tracks the sequence of events leading up to this possible situation.

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Modern Approaches to Accident Investigation

Management Oversight and Risk Tree (MORT)- Identifies the

causes for an accident and evaluates the systems and how it may have contributed to the failure.

Cost Benefits Analysis- Not accutually a

method of investigation, but helps to determine when safety items are benefiting the situation on a cost based level.

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Modern Approaches to Accident Investigation

Hazard Analysis- The identification of hazards before an

accident occurs. Assesses the degree of risk. W.T. Fine developed a formula for evaluation the risk in a situation:

R=C x E x PRisk Score=RPotential Consequences=CExposure=EProbability of occurrence=P

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Modern Approaches to Accident Investigation

Computer Profiles- A computer generate sentence made up of

several injury factors strung together in a format that uses connecting phrases that make the sentence intelligible and show a relationship between the factors.

The computer can then take many of these sentences and come up with a “trend” in the data. This can help in analyzing accidents of a certain nature.

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When System Safety Breaks Down

Sometimes a minor oversight can cause a great disaster, such as the tragic Challenger explosion in 1986.This is why the safety analysis's are so important for prevention of accidents.

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Summary

Statistical data is used to determine problem areas, and ultimately prevent accidents all together.Validity and Reliability are two factors that need to be taken into consideration when evaluating material-especially statistics.There are many systems in place to help prevent accidents from happening.

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Specific Death Rate = # of Deaths x 100,000

Specific Population

Foundry 4x 100,000 500 = 800

Mining 9x 100,000 1000 = 900

Lumber 14x 100,000 2000 = 700

Construction 18 x 100,000 3000 = 600