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Glossary

DC Motor

A heavy-duty electric motor designed for continuous operation.

Decibels

A unit of measurement for sound. Decibel levels are typically used to demonstrate how quietly a vacuum cleaner or air purifier operates. To provide a frame of reference, a sound at 15 decibels (dB) is very soft and at 100 dB is very loud.

Dehumidification

The process of removing moisture from the air within an indoor environment. This is important to reduce relative humidity levels below those that support mold and mildew growth. Dust mites levels may also be reduced when relative humidity (RH) levels are kept below 50%.

Direct Air System

See "Dirty-Air Design".

Direct Connect

Power team canisters that have electric power nozzles require that electricity travel from the canister to the power nozzle. In the past this was accomplished by attaching external cords to the hose and wands. Later, electric hoses were developed that had the electrical wires inside the hose with pigtails on either end. The Direct Connect system now eliminates both external cords on the hoses and wands as well as the pigtails. The electrical system is integrated into the hoses, wands and power nozzle and is automatically connected when the vacuum cleaner is assembled for use.

Dirty-Air Design

This is another term for "Direct Air" system and is a vacuum cleaner design where the airflow that picks up the soils passes directly through the motor fan before any filtration and then goes into the dustbag. Traditional uprights are most often designed using this system, which is known as a "Dirty Air" system because unfiltered air and soils passed through the motor. This often results in broken fans and other motor damage. Use of attachments in vacuum cleaners using this design is often awkward, requiring specialized adapters.

Drill Aerosols

In a dental office there are a number of sources of bacterial aerosols that may transmit disease to staff and patients. These include high speed drilling as well as ultrasonic scaling.

Dust Mites

Dust mites are microscopic, eight-legged creatures that are 250-300 micrometers in length (7,000 can fit on a fingernail) and are invisible to the naked eye.

Dust mites live on dead human skin cells, (which comprise up to 80% of house dust) as well as fungi and bacteria. They also live off water vapor, which humans provide for them by perspiration and respiration, emitting approximately one pint of moisture per person per night. This is why mites are found even in areas of extremely low humidity and prevention strategies such as reducing humidity levels in the home are generally ineffective. Dust mite feces contains a potent allergen thought to be responsible for as much as 25% of all allergies worldwide.

Physician organizations such as the American Academy of Allergy Asthma and Immunology (AAAAI) state that dust mite feces are a major source of allergen found in house dust. It is clear that dust mite feces is one of the most important and hazardous allergens found in indoor environments.

Dust Mite Feces

Dust mite feces contains two highly potent allergens Dermatophagoides pteronyssinus and Dermatophagoides farinae generally referred to as Der p1 & Der f1. A dust mite will produce 20 to 100 fecal pellets per day or 200 times its own body weight in feces during its short lifetime. If dust mite pellets were the size of golf balls, the average queen size bed would have a pile of pellets 70 feet high. A female dust mite will also lay 100 eggs during its approximately ten-week lifetime, with a new generation being produced about every three weeks.

During the night, most people toss and turn up to 60 or 70 times. This expels dust mite feces into the air from bedding and pillows. These allergens can then stay in the air for up to two hours. Once airborne, these potent allergens are inhaled where they can cause allergic illness in the first place and stimulate allergic reactions and asthma attacks in those that already have developed allergic disease. Other activities such as walking, vacuuming (with typical vacuum cleaners) and changing bed linens easily stir up dust mite allergens.

Dustbag Change Indicator

A display on a vacuum cleaner that informs the user that the dustbag needs changing. Given that a full dustbag can decrease cleaning ability and put unnecessary strain on the vacuum motor, this is an excellent feature. Also referred to as "Dustbag Indicator" or "Full Bag Indicator".

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