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Glossary

Dampers

Controls that vary airflow through an air outlet, inlet, or duct. A damper position may be immovable, manually adjustable, or part of an automated control system.

Deadleg

A length of pipe ending at a fitting through which water flows only when the fitting is opened.

Detergent

A cleansing agent capable of penetrating biological films, sludge and sediment and having the ability to emulsify oil and hold materials in suspension. Water treatment specialist have developed detergent formulations which are capable of thoroughly cleaning components which are difficult to access and inspect, such as cooling tower fill.

Developmental toxicant

A chemical that acts as a poison by means of causing adverse effects on the developing organism, including death, structural abnormality, altered growth, and functional deficiency.

Diagnosis

 

Investigation or analysis of the cause or nature of a condition, situation, or problem.

Diencephalon

5th division of the C.N.S.

Dilution

Additional air beyond that which is needed to provide combustion. This may either be within the combustion chamber as excess air or as induced flow in the exhaust stack.

Diposlide

A glass or plastic slide coated with culture media on which microorganisms can be grown and estimated. Legionella does not grow on these media.

Disinfectants

One of three groups of antimicrobials registered by EPA for public health uses. EPA considers an antimicrobial to be a disinfectant when it destroys or irreversibly inactivates infectious or other undesirable organisms, but not necessarily their spores. EPA registers three types of disinfectant products based upon submitted efficacy data: limited, general or broad spectrum, and hospital disinfectant.

Dose-response relationship

The effect of a substance on a body increases as the dose increases; theoretically, the body may respond differently at different dose levels of a given substance.

DPD Test Kit

A kit for measuring free, combined and total chlroine residuals using the reagent DPD (N, N-diethyl-p-phenylene diamine). Many test kits available from swimming pool suppliers measure only total chlorine not free chlorine and consequently should not be used. Free chlorine residuals in excess of 10 mg/L 10 ppm) are capable of bleaching the indicator colour, rendering the test invalid. Samples of water may have to be diluted with distilled water, or other water which does not interfere with the test, to bring the sample within the range of the kit. Allowance must be made for the sample dilution factor when determining the free chlorine residual in the original sample.

Dust spot efficiency

A measure (expressed in percent) of the ability of a filter to remove atmospheric dust from air.

Dysarthria

Difficulty speaking.

Dyscalculia

Inability to carry out mathematical calculations.

Dyslexia

Disorders with reading; congenital or acquired.

Dysphagia

Difficulty swallowing.

Dystonia

Abnormally increased muscular tone that causes fixed abnormal postures; sometimes shifting postures result from irregular, forceful twisting movements that affect the trunk and extremities.