safety factor
Information about safety factor
Factor of safety (FoS) can mean either the fraction of structural capability over that required, or a multiplier applied to the maximum expected load (force, torque, bending moment or a combination) to which a component or assembly will be subjected. The two senses of the term are completely different in that the first is a measure of the reliability of a particular design, while the second is a requirement imposed by law, standard, contract or custom. Careful engineers refer to the first sense as a factor of safety, or, to be explicit, a realized factor of safety, and the second sense as a design factor, but usage is inconsistent and confusing, so engineers need to be aware of both.
The realized factor of safety is just a definition and needs no elaboration.
Appropriate design factors are based on several considerations. Prime considerations are the accuracy of load and wear estimates, the consequences of failure, and the cost of overengineering the component to achieve that factor of safety. For example, components whose failure could result in substantial financial loss, serious injury or death usually can use a safety factor of four or higher (often ten). Non-critical components generally have a design factor of two. An interesting exception is in the field of aerospace engineering, where design factors are 1.50 – 3.00 because the costs associated with structural weight are high. This low design factor is why aerospace parts and materials are subject to more stringent quality control.
A factor of safety of 1.0 implies no "overengineering" (not exceeding design requirements). Many government agencies and companies require the use of a Margin of Safety (M.S.) to describe the ratio of the strength of the structure to the requirements. The relationship between M.S. and FoS is M.S. = FoS − 1. Margin of Safety is sometimes, but infrequently, used as a percentage, i.e., a 0.50 M.S vs. a 50% M.S. The equivalent factor of safety would be 1.5.
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The realized factor of safety is just a definition and needs no elaboration.
Appropriate design factors are based on several considerations. Prime considerations are the accuracy of load and wear estimates, the consequences of failure, and the cost of overengineering the component to achieve that factor of safety. For example, components whose failure could result in substantial financial loss, serious injury or death usually can use a safety factor of four or higher (often ten). Non-critical components generally have a design factor of two. An interesting exception is in the field of aerospace engineering, where design factors are 1.50 – 3.00 because the costs associated with structural weight are high. This low design factor is why aerospace parts and materials are subject to more stringent quality control.
A factor of safety of 1.0 implies no "overengineering" (not exceeding design requirements). Many government agencies and companies require the use of a Margin of Safety (M.S.) to describe the ratio of the strength of the structure to the requirements. The relationship between M.S. and FoS is M.S. = FoS − 1. Margin of Safety is sometimes, but infrequently, used as a percentage, i.e., a 0.50 M.S vs. a 50% M.S. The equivalent factor of safety would be 1.5.
Real world examples
Steam boilers
The factor of safety used in steam boilers is usually between 8 and 10. For example, if the required working pressure is 250 pounds per square inch (psi), and the safety factor is 10, the bursting point must be not less than 2,500 psi. This allows a large margin of safety in a new boiler but, as the boiler ages and is affected by corrosion, the margin of safety will diminish. For this reason, steam boilers are hydraulically tested, at regular intervals, to 1.5 times or 2 times the working pressure.Pharmaceuticals
Even the most gentle of drugs, such as penicillin, can cause death when administered at excessively large quantities. The farther away the effective dose (ED) is from the lethal dose (LD) defines the margin of safety, or the natural, built-in safety factor, for that particular drug. For example, the effective dose of penicillin, i.e. the quantity that will be effective in treating an infection, is so vastly minute in relation to the multiplicity of doses necessary to prove fatal that penicillin is considered an extremely safe drug.See also
The term multiplier may refer to:
In electrical engineering:
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In electrical engineering:
- Multiplication ALU, a digital circuit that multiplies two numbers in a digital system
- Analog multiplier, a device that multiplies two analog signals
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In physics, force is an action or agency that causes a body of mass m to accelerate. It may be experienced as a lift, a push, or a pull. The acceleration of the body is proportional to the vector sum of all forces acting on it (known as net force or resultant force).
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torque (or often called a moment) can informally be thought of as "rotational force" or "angular force" which causes a change in rotational motion. This force is defined by linear force multiplied by a radius.
The SI unit for torque is the newton meter (N m). In U.S.
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The SI unit for torque is the newton meter (N m). In U.S.
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Aerospace engineering is the branch of engineering that concerns aircraft, spacecraft, and related topics. Aerospace Engineering was originally known as aeronautical engineering and dealt solely with aircraft.
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'For the Jurassic 5 album, see Quality Control (album)'
In engineering and manufacturing, quality control and quality engineering are involved in developing systems to ensure products or services are designed and produced to meet or exceed customer requirements.
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In engineering and manufacturing, quality control and quality engineering are involved in developing systems to ensure products or services are designed and produced to meet or exceed customer requirements.
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A boiler is a closed vessel in which water or other fluid is heated. The heated or vaporized fluid exits the boiler for use in various processes or heating applications.[1][2]
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Overview
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pound per square inch or, more accurately, pound-force per square inch (symbol: psi or lbf/sq in) is a unit of pressure or of stress based on avoirdupois units.
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Corrosion is breaking down of essential properties in a material due to reactions with its surroundings. In the most common use of the word, this means a loss of an electron of metals reacting with water and oxygen.
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drug, broadly speaking, is a substance used as a medicine or narcotic.[1] There is no single, precise definition, as there are different meanings in medicine, government regulations, and colloquial usage.[2]
In pharmacology, Dictionary.
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In pharmacology, Dictionary.
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Penicillin (sometimes abbreviated PCN) is a group of beta-lactam antibiotics used in the treatment of bacterial infections caused by susceptible, usually Gram-positive, organisms.
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Death is the permanent end of the life of a biological organism. Death may refer to the end of life as either an event or condition.[1] Many factors can cause or contribute to an organism's death, including predation, disease, habitat destruction, senescence,
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effective dose is the amount of drug that produces a therapeutic response in 50% of the people taking it. In radiation protection effective dose is an estimate of the stochastic effect that a non-uniform radiation dose has on a human.
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A lethal dose (LD) is an indication of the lethality of a given substance or type of radiation. Because resistance varies from one individual to another, the 'lethal dose' represents a dose (usually recorded as dose per kilogram of subject body weight) at which a given
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Limit state design (LSD) refers to a design methodology used in structural engineering. The methodology is in fact a modernization and rationalization of engineering knowledge which was well established prior to the adoption of LSD.
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In total quality management, TQM, redundancy in quality or redundant quality means quality which exceeds the required quality level. Tolerances may be too accurate, for example, creating unnecessarily high costs of production.
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Introduction
Probabilistic design is a discipline within Engineering Design. It deals primarily with the consideration of the effects of random variability upon the performance of an engineering system during the design phase...... Click the link for more information.
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