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Fundamental Concepts & Terms in Safety. TM 650 Safety Management Summer 2007. Reading Assignment. Read Chapter 3, Asfahl For this week Read Chapter 4, Asfahl For last week. Why should a company address safety?. Regulatory Reasons? Humanitarian Reasons? Economic Reasons?.

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fundamental concepts terms in safety

Fundamental Concepts & Terms in Safety

TM 650

Safety Management

Summer 2007

reading assignment
Reading Assignment
  • Read Chapter 3, Asfahl
    • For this week
  • Read Chapter 4, Asfahl
    • For last week
why should a company address safety
Why should a company address safety?
  • Regulatory Reasons?
  • Humanitarian Reasons?
  • Economic Reasons?
what is an accident
What is an Accident?
  • An event that is not expected or intended
  • Could cause
    • injury
    • loss
  • Implies “chance”
types of losses




damage to property, equipment, materials

cost of replacement

legal & medical services

Loss of time, production, sales

time to complete forms




hospitalization, rehab

public image damage

Types of Losses
losses direct vs indirect costs
Losses: Direct vs. Indirect Costs
  • Direct (Obvious)
    • medical expenses, WC, repair or replace damages
  • Indirect (Not Obvious)
    • 4:1 Ratio (Iceberg Theory)
    • Injured worker’s wages, lost supervisory time, co-workers’ lost time during emergency, damaged equipment, ruined product, overtime for production to catch back up, learning curve for replacement worker, clerical costs, payments made to injured under benefits program
fundamental accident causes
Fundamental Accident Causes
  • Unsafe Acts
  • Unsafe Conditions
  • Both
  • “Not necessarily a ‘chance’ event”
unsafe acts vs unsafe conditions
Unsafe Acts vs. Unsafe Conditions
  • Heinrich analyzed 75,000 accidents
  • 88 : 10 : 2 ratio
  • 88% unsafe acts
  • 10% unsafe conditions
  • 2% unpreventable causes
  • Engineers can attack unsafe conditions
  • Must understand human behavior and management principles to attack unsafe acts
accident injury relationship
Accident - Injury Relationship
  • Heinrich’s 300 : 29 : 1 ratio
  • For 330 accidents
    • 300 result in no injury
    • 29 produce minor injuries
    • 1 produces major, lost-time injury
  • Opportunities to improve are great
  • Many accidents are “rehearsed” many times
validity of heinrich s data
Validity of Heinrich’s Data
  • Heinrich’s concepts are classic, but the validity of his data has been called into question in recent years
  • Apparently the data upon which Heinrich published his work is not available and has not been replicated successfully in other studies
  • Regardless, his concepts provide excellent points for our thoughts
accident costs relationship
Accident - Costs Relationship
  • Pareto Analysis or Relationship
  • 80% - 20% rule
    • 80% of the costs are related to 20% of the injuries
    • for example, low back lifting injuries represent 20% of all accidents, but represent 80% of the costs
    • if you can manage and control that 20% of accidents, you can control 80% of the costs
  • Next slide shows 50% of the costs are related to 2% of the injuries - “the powerful few”
  • And 67% of the injuries represent 6% of the total cost – “you could spend a lot of time on these and save very few $”
  • Safety: being relatively free from harm, danger, damage, injury
  • Risk: measure of both frequency and severity of hazards
  • Hazard: unsafe condition, the potential for an activity or condition to produce harm
accident theories
Accident Theories
  • Domino Theory
  • Energy Theory
  • Single Factor Theories
  • Multiple Factor Theories
domino theory heinrich
Domino Theory (Heinrich)
  • Injury is caused by
  • Accidents which are caused by
  • Unsafe acts or conditions which are caused by
  • Undesirable traits (e.g., recklessness, nervousness, temper, lack of knowledge, unsafe practices) which are caused by
  • Social environment
domino theory cont
Domino Theory Cont.
  • Stop the sequence by removing or controlling contributing factors
  • Strong emphasis is placed on the middle domino: unsafe acts or conditions
energy theory haddon
Energy Theory (Haddon)
  • Accidents & Injuries involve the transfer of energy, e.g., fires, vehicle accidents, projectiles, etc.
  • Transfer of energy from a “potential” to “kinetic”
  • Attack problems in parallel rather than serial (as is presumed in Domino Theory)
energy theory cont 10 strategies to prevent or reduce
Energy Theory Cont.10 Strategies to Prevent or Reduce

1. Prevent the marshalling of energy

- don’t produce the energy

- don’t let kids climb above floor level

- don’t produce gun powder

2. Reduce the amount of energy marshalled

- keep vehicle speeds down

- reduce chemical concentrations

- don’t let kids climb above 3’


3. Prevent the release of energy

- elevator brakes

4. Modify the rate at which energy is released from its source or modify the spatial distribution of the released energy

- reduce the slope on roadways

5. Separate in space or time the energy being released from the structure that can be damaged or the human who can be injured

- separate pedestrians from vehicles


6. Separate the energy being released from a structure or person that can suffer loss by interposing a barrier

- safety glasses, highway median barriers

7. Modify the surfaces of structures that come into contact with people or other structure

- rounded corners, larger surface areas for tool handles

8. Strengthen the structure or person susceptible to damage

-fire or earthquake resistant structures, training, vaccinations


9. Detect damage quickly and counter its continuation or extension

- sprinklers that detect heat

- tire tread wear bands

10. During the period following damage and return to normal conditions, take measures to restore a stable condition

- rehab an injured worker

- repair a damaged vehicle

single factor theories
Single Factor Theories
  • Assumes that when one finds a cause, there is nothing more to find out
  • Weak theory, there can be so much more to learn!
multiple factor theories
Multiple Factor Theories
  • Accidents are caused by many factors working together
  • The theory and the analysis is more complex, but more realistic than Single Factor Theory
  • Consider the Four M’s:
    • management, man, media, machine
    • And their interactions
concepts of hazard avoidance
Concepts of Hazard Avoidance
  • Approaches
    • Enforcement
    • Psychological
    • Engineering
    • Analytical
  • To be successful you must have top management support!
1 enforcement approach
1. Enforcement Approach
  • Your approach to hazard avoidance is entirely predicated upon avoiding regulatory fines.
  • Many companies establish their safety programs to meet OSHA requirements thinking that is adequate.
  • This is a bare minimum approach. While it may seem cost effective, it likely is not in the big picture.
2 psychological approach
2. Psychological Approach
  • Your approach to hazard avoidance is based on a psychological (or behavior-based) approach.
  • The behavioral approach has been popular and widely used.
    • DuPont STOPTM (Safety Training Observation Program)
  • To be successful, this approach needs to be ever vigilant, and must be infused with some engineering and analytical components
3 engineering approach
3. Engineering Approach
  • The engineering approach to hazard avoidance utilizes controls measures starting with engineering (then administrative, then PPE)
  • Consideration of (see next slides)
    • Safety Factor Concept
    • Fail-Safe Concept
    • Design Principles – Design for Safety
  • Be careful to avoid a false-sense of security from engineering and technology
    • read Case Study 3.7
    • Casey books
recommendation for reading
Recommendation for Reading:
  • Set Phasers on Stun: And Other True Tales of Design, Technology, and Human Error. Steven Casey. Aegean Publishing Company, Santa Barbara, CA. 1993. ISBN: 0-9636178-7-7
  • The Atomic Chef: And Other True Tales of Design, Technology, and Human Error. Steven Casey. Aegean Publishing Company, Santa Barbara, CA. 2006. ISBN: 0-9636178-6-9
safety factor concept
Safety Factor Concept
  • Since there is a chance element in safety, we can improve our chances by implementing a “safety factor”
    • Scaffolding – 4:1
      • Designed to withstand 4 times the intended load
    • Overhead crane hoists – 5:1
    • Scaffold ropes – 6:1
  • Why not use 10:1 as a standard?? $$$$$
  • Beware when using field tables or computer programs. Are the safety factors applied or not??
fail safe concept
Fail-Safe Concept
  • General fail-safe principle
    • The resulting status of a system, in event of failure of one of its components, shall be in a safe mode.
    • Read Case Studies 3.5 and 3.6
  • Fail-safe principle of redundancy
    • A critically important function of a system, subsystem, or components can be preserved by alternative parallel or standby units.
  • Principle of worst case
    • The design of a system should consider the worst situation to which it may be subjected in use.
    • Murphy’s Law: If anything can go wrong, it will.
engineering design principles




Warn with alarms (auditory, visual)



Exhaust ventilation

Human Interface

Engineering Design Principles
4 analytical approach
4. Analytical Approach
  • The analytical approach to hazard avoidance utilizes various qualitative and quantitative tools
    • Accident Analysis
    • System Safety Techniques (see next slide)
    • Loss Incident Causation Models
      • Proximal and Distal Causes (McClay)
    • Toxicology
    • Epidemiology
    • Cost-Benefit Analysis
system safety techniques
Preliminary Hazard Analysis

Hazard Tracking Log

Subsystem Hazard Analysis

System Hazard Analysis

Operating Hazard Analysis

Change Analysis

Accident Analysis

Time-Loss Analysis

Event and Causal Factor Charts

Process Safety Management

Fault Tree Analysis (FTA)

Energy Trace & Barrier Analysis (ETBA)

Failure Mode & Effects Analysis (FMEA)

Project Evaluation Tree (PET)

Management Oversight & Risk Tree (MORT)

Software Hazard Analysis

Common Cause Failure Analysis

Sneak Circuit Analysis

System Safety Techniques
how safe is safe enough
How Safe is Safe Enough?
  • Can absolute safety be achieved?
  • Remember the concept of “risk”.
  • What is “acceptably safe”?
  • Remember the Risk Assessment Matrix: Severity versus Frequency
  • In addition to Asfahl
  • Brauer RL. Safety and Health for Engineers, 2nd edition, Wiley, 2006.
  • Manuele FA. On the Practice of Safety, 3rd edition, Wiley, 2003.
  • Stephans RA. System Safety for the 21st Century, Wiley, 2004
hw7 chapter 3
HW7 – Chapter 3
  • Exercises & Study Questions
    • 1-41, divisible by 5
  • Research Exercises
    • 42-45, pick one
  • Standards Research Questions
    • 46-48, pick one
  • 30 points, due asap
hw8 chapter 4
HW8 – Chapter 4
  • Exercises & Study Questions
    • 1-29, divisible by 5
  • Research Exercises
    • 30-40, pick one
  • Standards Research Questions
    • 41-43, pick one
  • 30 points, due asap
hw9 hazard awareness advisor
HW9 – Hazard Awareness Advisor
  • Go to
  • Select “e-tools”
  • Go to “Expert Advisors”
  • Select “Hazard Awareness” and download it to your computer or run it online
  • Run this “expert system” to evaluate your workplace or someplace you have worked.
  • Write a one page memo that describes what you have learned from this exercise. I especially want to know if you’ve learned of some new workplace hazards. Do you think this is a useful tool for industry?
  • 15 points, due asap