Glossary of Terms: D

dBA
Decibels, relative to the A weighting scale (as affected by the human ear).
Decibel (dB)
Sound Level Meters use the decibel as the unit of measure known as Sound Pressure Level (SPL). SPL uses the ratio between a reference level of 20 microPascals (.00002 Pascals) and the level being measured. SPL = 20 log (measured level/reference level).
Decomposition
The breakdown of a material or substance (by heat, chemical reaction, rotting or other process) into parts or elements.
Degrees Celsius (Centigrade)
The temperature on a scale in which the freezing point of water is 0oC and the boiling point is 100oC. To convert to Degrees Fahrenheit, use the following formula: oF = (oC x 1.8) + 32.
Degrees Fahrenheit
The temperature on a scale in which the boiling point of water is 212oF and the freezing point is 32oF.
Density
The mass per unit volume of a substance. For example, lead is much more dense than aluminum.
Dermal
Relating to the skin.
Dermatitis
Inflammation of the skin. Symptoms of dermatitis may include redness, blisters, and cracks in the skin.
Dermatosis
A broader term than dermatitis; it includes any cutaneous abnormality, thus encompassing folliculitis, acne, pigmentary changes, and nodules and tumors.
Division
North American area classification of a hazardous area (Division 1 or 2) that defines the length of time a hazard in present.
DOL
US Department of Labor. OSHA and MSHA are part of the DOL.
Dose
Related to the Criterion Level, a dose reading of 100% is the maximum allowable exposure to accumulated noise. For OSHA, 100% dose occurs for an average sound level of 90 dB over an 8 hour period (or any equivalent exposure). By using a TWA reading rather than the average sound level, the time period is no longer explicitly needed. A TWA of 90 dB is the equivalent of 100% dose. The dose will double (halve) every time the TWA increases (decreases) by the Exchange Rate.
Dose-response relationship
Correlation between the amount of exposure to an agent or toxic chemical and the resulting effect on the body.
DOT
Department of Transportation.
Duct
A conduit for conveying air at various pressures
Dust
Fine particles of a solid that can remain suspended in air. The particle size of a dust is larger than that of a fume. Dusts are produced by mechanical action, such as grinding. Some dusts may be harmful to an employee’s health. See respirable particles.
Dusts
Solid particles generated by handling, crushing, grinding, rapid impact, detonation, and decrepitation of organic or inorganic materials, such as rock, ore, metal, coal, wood and grain. Dusts do not tend to flocculate, except under electrostatic forces; they do not diffuse in air but settle under the influence of gravity.
Dynamic range
Sometimes called Linear Range. This is the range of input amplitudes on any given range setting over which the instrument can produce a meaningful response. The bottom of the dynamic range is the instrument’s Noise Floor for that range setting, and the top of the dynamic range is the maximum input signal that will not overload the instrument on that range setting.
Dyspnea
Shortness of breath, difficult or labored breathing.