SAFE 605: Principles of Safety Engineering Overview of Safety Engineering Safety Engineering Concepts

Safety Engineering Safety engineering is devoted to the application of scientific and engineering principles and methods to the elimination and control of hazards. Safety engineering is an applied science strongly related to systems engineering. Safety engineering assures that a life-critical system behaves as needed even when pieces fail.

Safety Engineering Defined To regulate the effects of hazards, it is necessary to employ a means of controlling the causes responsible for the presence of injurious agents. This is the essence of the practice of safety engineering.  Grimaldi and Simonds

Application of the Sciences Safety engineering applies the sciences to situations in an attempt to reduce the likelihood of the occurrence of unwanted events These events include accidents, injuries, property losses, and financial losses

Civil Engineering Safety engineering in the area of civil engineering includes: Knowledge of structural integrity of buildings and bridges An understanding of the needs for controlling air pollution and water pollution Knowledge of the planning required to build safe roads and highways

Industrial Engineering Industrial engineers are responsible for the design of production processes. A major safety issue for industrial engineers involves the reduction of ergonomic hazards in the workplace.

Hazard Control Methods Engineering controls Administrative Controls PPE Training

Hazard Control Priorities Eliminate the hazard Reduce the hazard level Provide safety devices Provide warnings Provide safety procedures

Definitions A "fault" is said to occur when some piece of equipment does not operate as designed. A "failure" only occurs if a human being (other than a repair person) has to cope with the situation. A "critical" failure endangers one or a few people. A "catastrophic" failure endangers, harms or kills a significant number of people. Safety engineers also identify different modes of safe operation:

Definitions A "probabilistically safe" system has no single point of failure, and enough redundant sensors, computers and effectors so that it is very unlikely to cause harm (usually "very unlikely" means less than one human life lost in a billion hours of operation). An "inherently safe" system is a clever mechanical arrangement that cannot be made to cause harm- obviously the best arrangement, but this is not always possible. A "fault-tolerant" system can continue to operate with faults, though its operation may be degraded in some fashion.

Fail-Safe Designs A "fail-safe" system is one that cannot cause harm when it fails. Fail-passive arrangements: Reduces the system to the lowest energy level Will not operate again until problem is resolved Fail-active design: Keeps system in safe operating mode until corrective action is taken Battery operated smoke detector in which an alarm continues to sound in the event of a failure. Fail operational arrangement: Allows system to operate until corrective action is possible. Excess pressure valve design in a pressure vessel allows the valve to remain open and usable until a replacement valve can be installed.

Safety Factors Expressed as a ratio between strength and stress. A safety factor for a wire rope is the ratio between the force required to break the rope (nominal breaking strength) and the rated load (load which should never be exceeded while lifting

Failure Rate Reduction Uses components in a design arrangement that produces expected lifetimes far beyond their proposed periods of use. Methods of reducing failure rates include: Screening Redundant arrangements Timed replacements Derating

Reducing stresses upon components thereby increasing their life and reliability Example: Providing fans in computers to reduce the heat generated by the electronic components

Screening Quality control Statistical process control Visual inspection and measurement

Timed Replacements The practice of timed replacements involves the establishment of a preventive maintenance program in which parts which are subject to fail, are replaced on a schedule that ensures they are replaced prior to failure.

Redundancy Redundacy involves the use of backup subsystems designed to take over the operation of a system in the event of failure of the primary subsystem.

Primary Causes of Engineering Disasters The primary causes of engineering disasters are usually considered to be: human factors (including both 'ethical' failure and accidents) design flaws (many of which are also the result of unethical practices) materials failures extreme conditions or environments Most commonly and importantly, most disasters are a combination of these reasons.

A Study of Engineering Failures The Swiss Federal Institute of Technology in Zurich analyzed 800 cases of structural failure in which 504 people were killed, 592 people injured, and millions of dollars of damage incurred. When engineers were at fault, the researchers classified the causes of failure as follows: Insufficient knowledge, 36% Underestimation of influence 16% Ignorance, carelessness, negligence, 14% Forgetfulness, error, 13% Relying upon others without sufficient control, 9% Objectively unknown situation, 7% Imprecise definition of responsibilities, 1% Choice of bad quality, 1% Other, 3%

Engineering Ethics Often, a deficiency in engineering ethics is found to be one of the root causes of an engineering failure. An engineer, as a professional, has a responsibility to their client or employer, to their profession, and to the general public, to perform their duties in as conscientious a manner as possible.

Ethical Duty An ethical engineer is one who avoids conflicts of interest, does not attempt to misrepresent their knowledge so as to accept jobs outside their area of expertise, acts in the best interests of society and the environment, fulfills the terms of their contracts or agreements in a thorough and professional manner, and promotes the education of young engineers within their field.

Math Review First homework assignment is to “test” your math skills There will not be calculus based formulas in the course. If you can’t do them, don’t lose sleep over them The course will be using algebra, trig, finite math, and physics