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Home > Forensics > Human Factors Glossary 

Selected Glossary of Human Factors and Safety Terms


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Landing. A level walking surface at the top and bottom of a stairway or ramp, or between flights of stairs.

Legibility. The degree to which an alphanumeric character can be distinguished from another; depends on attributes such as stroke width, contrast, and illumination. See Readability.

Light adaptation. The physical and chemical adjustments of the eye and visual system that reduces sensitivity to light as levels of illumination are increased.

Lockout. Means for assuring that machines are not turned on while being serviced. A lock is placed on the power switch or control box so that operators and others may not turn on the machine until the lock is removed by the person performing the service. Lockout is considered more reliable than "tagout". See Tagout.

Luminance. The amount of light reflected from an object or surface. Measured in candelas per square meter (cd/m2), or foot Lamberts (fL).

Lux (lx). A measure of illuminance, in lumens per square meter.

lx. See Lux.

Machine guard. A rigid shield or device that covers hazard points on a machine to prevent accidental and injurious contact with body parts, or to control hazardous ejection and emissions from the machine such as flying chips, air contaminants and noise. Syn. Barrier guard.

Nosing. The forward edge of a stair tread that extends past the riser.

OSHA. Occupational Safety and Health Administration. Part of the U.S. Department of Labor, a federal agency created in 1971 that has regulatory and enforcement authority to ensure safe workplaces in the United States [OSHA Web site].

Pedestrian. A person using legs or leg surrogates (for example, prosthetic limbs, crutches, etc.) as the principle method of locomotion. [ASTM F1646-02].

Peripheral vision. Vision in the region of the visual field that is supported by visual receptors outside of the fovea.

Personal protective equipment (PPE). Safety devices or safeguards worn by workers to protect against environmental hazards. PPE includes helmets, safety goggles, hearing protectors, face shields, respirators, arm guards, smocks, gloves, and safety boots.

Photometry. The measurement of the properties of light that have an effect on vision.

Photopic. Related to daytime illumination levels in which the eye is adapted to light and vision is supported by the cone photoreceptors.

Photoreceptor. A specialized nerve ending, such as a rod or cone cell in the retina of the eye, that is sensitive to light.

PPE. See Personal Protective Equipment.

Ramp. A walkway surface with a slope greater than 1:20 (5%).

Reaction time. The time it takes to search for a signal, detect it, interpret its meaning, decide on a response to the signal, and implement the response to the signal. Reaction time, which typically ranges from less than one second to over five seconds, can be affected by a number of environmental factors, including signal quality, signal probability, number of possible responses, and complexity of the required response. Individual factors also may affect reaction time. Such factors may include a person's age, familiarity with the situation, fatigue, ingestion of medication or other drugs, and mental workload.

Readability. The degree to which the information content represented by groups of alphanumeric characters--words, sentences, or continuous text--can be understood; depends on attributes such as the spacing of characters and the spacing between lines of characters. See Legibility.

Rise. The vertical height of something, such as the rise of a stair or ramp.

Riser. In a stairway, the vertical face between two treads.

Risk. A measure of the probability and severity of injury, illness, loss, or other adverse effects.

Rod. A rod-shaped photoreceptor in the retina of the eye that responds to low levels of illumination. Rods are located only outside of the fovea.

Run. The horizontal extent of something, such as the horizontal distance covered by a stairway or ramp. In a stairway, the horizontal length of the tread, measured from the face of one riser to the face of the next, excluding the nosing.

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