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Exposure versus Dose

Exposure versus Dose

Posted by Dr. David J. Silver, B.S., M.S. Ph.D., CIH on Apr 12th 2019

Recognition, Evaluation, and Control

Evaluations of workplace airborne hazards involve preparation, knowledge of materials, processes, and the population at risk. Just because there is a harmful material present doesn’t mean that a person cannot work with it. Any material, no matter how inherently dangerous it is, can be controlled, isolated, or shielded, so that it is safe to work with. If the harmful material is not able to come in contact with the person, that person is protected from its harmful effects. Many people work with radioactive materials, hydrogen cyanide, and deadly microorganisms like the Ebola virus. We will explore the dangers and the ability to work with these inherently dangerous materials.

Sufficient Quantity to Cause Harm

Just because a toxin is present does not mean it is in sufficient quantity to cause harm. Think of almonds, they contain cyanide. How about asbestos vinyl flooring? The fibers are bound up in an elastic matrix and if not acted on by grinding or sanding, fibers cannot be liberated to become an inhalation hazard. Low concentrations of solvent vapors cause dizziness, epoxies cause dermatitis, and inhalation of a significant concentration of hydrogen sulfide or hydrogen cyanide can cause death. Eating five pounds of butter in one sitting can lead to death.

Exposure Does Not Equal Dose

Exposure is about the chemicals that you come in contact with through breathing, eating, drinking, injection, and skin contact. Many substances have the ability to cause harm locally or systemically throughout the organs and body. The exposure can be there, however, protective clothing or respiration will prevent one from taking in the substance. The dose, the amount of substance a human body can take in, is different for many. The ability of substances to enter the human body differs by inhalation rate, skin health, size, and age.

Dose – Response

Paracelsus (1493–1541) established that the ability of a chemical substance to cause adverse effects is based on the dose response theory. The quantity or the dose of the substance determines whether the effects of the chemical are toxic, nontoxic or beneficial. In addition to dose, other factors may also influence the toxicity of the compound such as the route of entry, duration and frequency of exposure, variations between different species (interspecies), and variations among members of the same species (interspecies).

Routes of Entry

The dose is the total amount of chemical absorbed during an exposure. The dose depends on the concentration of the chemical and duration (contact time) of the exposure. Chemicals cause predictable toxic effects based on the dose. Exposures may be acute, sub-acute, or chronic and may result in acute, sub-acute, or chronic health outcomes. Please refer to any of the modern toxicology references available in book form or on the internet.

Chemicals may enter the body through different routes of entry:

Inhalation exposure – Gases, vapors, airborne powders, and aerosolized liquids are inhalation risks.

Dermal exposure – Chemicals in contact with the skin can cause local effect but may also enter the systemic circulation and cause effects at distant sites from the entry route.

Ingestion – Inadvertently swallowing chemicals can happen, especially if eating is allowed in chemically dirty environments.

Injection – sharp edges or pokey equipment, if contaminated with highly toxic chemicals, may cause these toxins to enter the bloodstream.

Determine the Exposure

Your evaluation of the workplace begins with the materials and process surveys to estimate where you think exposures are and how they have to be controlled. Over exposures may be indicated when you consider that some workers may be affected as signified by complaints, medical exams, and symptoms. Measurement of airborne substances in conjunction with a good engineering or administrative control program will go a long way to reducing employee sickness and lost work time.

Industrial hygiene equipment can be employed to measure these exposures. Direct reading instruments and airborne media sampling and analysis can help pinpoint where controls or substitutions need to be made.

EGas Depot for Your Industrial Hygiene Equipment Needs

Count on EGas Depot for your industrial hygiene equipment needs. We have an assortment of calibration gases, gas meters, gas meters with PIDs, sound level meters, noise dosimeters, and air sampling equipment, air sampling media, heat stress monitors, and dust monitors. We offer Gas Clip, MPower, Casella, Dwyer, calibration gas, Elk River, and Allegro products. A full line from Casella and Dwyer Industries are available at EGas Depot www.egasdepot.com or call toll free at 833-264-0730.

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