As scientists measure and study very small amounts of particles, they may refer to “parts per” when talking about contents, or concentrations, of a chemical in air or water.  When scientists measure down to parts per million, billion or trillion, it is important to have some sense of just how much—or how little—they are talking about.  

A part per million may be hard to comprehend or visualize. Want to see how much it is?

It’s a credit card lying in the middle of a football field.

One step, on a 568-mile walk.

Or one minute, in a two-year span.

What’s A Part per Billion?

Taking that further, a part per billion is one thousand times smaller than that credit card on the football field, for example, or one heartbeat in 27 years for an average male (70 heartbeats per minute).

When it comes to substances we take in when we eat, breath, or absorb something through our skin, the comparisons are made relative to body weight. Normally scientists talk in terms of “milligrams (of material ingested) per kilogram (of body weight).” A milligram is one thousandth of a gram (a gram is about 3/100 of an ounce), and a kilogram is one thousand grams (or about two pounds). A milligram of a material ingested per kilogram of body weight is the equivalent of one part per million.

Want to see what taking in a milligram per kilogram of your body weight amounts to?

It’s the equivalent of 726 people, each weighing 150 pounds, sharing a chocolate bar

Obviously, none of those people is going to get a very large piece of that chocolate bar. Now if that were an equivalent amount of a deadly poison such as cyanide, it might still cause some harm. That is why those tests on rodents are done—to reveal how much of a particular substance it would take to cause a negative health effect, at least in rodents. Although the results of rodent testing may not always be relevant to humans, they are generally used as a basis for establishing safe levels of exposure to a substance.

What about Aliphatic Diisocyanates?

Where do aliphatic diisocyanates come in to this picture? To protect consumers and workers, a robust system of regulations and industry initiatives oversees the use of chemicals, including aliphatic diisocyanates. The ADI industry, in cooperation with many government agencies, is committed to enhancing scientific understanding and making safety information available. Visit the Consumer Safety and Aliphatic Diisocyanates section to learn more. 

Specific to worker safety, regulatory authorities and other related organizations in many countries have devised and adopted occupational exposure limits (OELs) for aliphatic diisocyanates. Occupational Exposure Limits (OELs) are intended to set the airborne concentrations of substances to which workers can be exposed, on a daily basis without significant risk of material adverse effects. OELs are normally set for an eight-hour day and are expressed as an eight-hour time-weighted average (TWA). In many cases, a short-term (15-minute) exposure limit or Ceiling (C) value is also established. Occupational exposure limits can be called by different names such as: recommended exposure limits (REL); threshold limit values (TLV); and permissible exposure limits (PEL). 

The primary regulatory and professional organizations that have established OELs for airborne aliphatic diisocyanates include:

The Occupational Safety and Health Administration (OSHA) has not established PELs for aliphatic diisocyanates. 

To help protect workers, the ADI industry uses many tools to monitor potential worker overexposure. To view these methodologies as well as the OELs established for aliphatic diisocyanates, visit the Industrial Hygiene section. Current regulations should always be consulted for compliance purposes. 

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