Can You Tell Me More About
the Toxicity of nPB?

MicroCare Marketing Services distributes the Bromothane™ family of solvent cleaners across North America. These chemicals are manufactured by the Great Lakes Chemical Corp. of Indiana. Great Lakes and MicroCare have established an Acceptable Exposure Limit (AEL) of 10 parts per million (ppm), using the 8- time weighted average (TWA) methodology. Users can be confident that Bromothane™ solvents have low toxicity risks if worker exposures are limited to the recommended 10 ppm time-weighted average exposure.

Let's take a look at the details.

• An Official TLV for nPB Has Now Been Established •

In 2005 and after years of research and deliberations, the American Conference of Industrial Hygienists (ACGIH) finally finalized and established a "Threshold Limit Value" (TLV) of 10 parts-per-million for an eight-hour time-weighted workday. This TLV applies to the "Bromothane™" brand solvents sold by MicroCare and to all other versions on nPB marketed by other companies under their own brand names.

TLVs established by the ACGIH have long been recognized as the "official" value that most health professionals reference when looking for guidance on exposure limits. The establishment of a new TLV is a lengthy, open, peer-reviewed process. Persons having views contrary to the proposed ratings are given years to provide new information or other data that is persuasive enough to change the proposed standard. Apparently nobody had enough convincing evidence to cause the TLV committee to move up or down from 10 ppm.

According to the ACGIH web site, "The American Conference of Governmental Industrial Hygienists (ACGIH®) is a member-based organization and community of professionals that advances worker health and safety through education and the development and dissemination of scientific and technical knowledge...For over 60 years, ACGIH® has been respected for its dedication to the industrial hygiene and occupational health and safety industries. [ The ACGIH mission is ] to provide essential, cutting edge information to government, academia, and corporate facilities throughout America, Canada and countries abroad."

The decision on the TLV of nPB was not without controversy. For example, MicroCare and our supplier of Bromothane, Great Lakes Chemical, have asserted for years the proper TLV should be 10 ppm. All of MicroCare's literature and customer support are based upon this exposure level. Other companies had urged higher threshold levels, as high as several hundred ppm, but the ACGIH chose to disagree with their findings.

In fact, one trade association went to court in an attempt to block the publication of the ACGIH standard. In a Nov. 30, 2004 press release, the ACGIH noted that the case involved ACGIH's proposed toxicity ratings on n-Propyl Bromide. But the court found the lawsuit was without merit. The chairman of ACGIH's board, Vickie L. Wells, MS, CIH, CSP, stated, "We stand by our [ACGIH's] policies, procedures and processes. We stand by our recommended Threshold Limit Values, and the fairness and thoroughness of the system used in their development and dissemination." (Just for the record, the following comments are equally applicable to any brand or source of n-Propyl Bromide, also known as nPB, 1-Bromopropane or CAS # 106-94-6.)

• The Hazards Associated with nPB •

In simple terms, the hazards associated with n-propyl bromide can be viewed with regards to short and long term exposure. Like other solvents, short-term over-exposure can lead to skin irritation and dizziness. From a long-term exposure viewpoint, tests in animals have shown long-term overexposure to nPB may lead to multiple adverse affects in the body likely including fertility problems for both males and females. The U.S. National Toxicology Program has recommended a No Observable Adverse Effect Level (NOAEL)for nPB of 100 ppm which leads to the normal one-tenth exposure level recommendation of 10 ppm. Howver, there are differing opions on this matter. The U.S. E.P.A. has set a recommended safety level of 25 ppm, and other vendors recommend even higher levels. At this time, however, both MicroCare and Great Lakes feel strongly the 10 ppm exposure limit is the a cautious and proper recommendation.

Consult the most recent Bromothane MSDS for a complete and up to date review of health hazards.

• About TWA, TLV and AEL Toxicity Ratings •

In general, "toxicity" is measured through the use of 8- and 12-hour "time-weighted average exposure limits" (AEL). Similar terms you might find on labels and MSDS sheets include "Average Exposure Limits" (AEL), "Personal Exposure Limits" (PEL) and "Threshold Exposure Limits" (TEL). One special term are the "Threshold Limit Values" (TLVs) which only are established by the American Conference of Governmental Industrial Hygienists (ACGIH).

It is prudent to understand the underlying basis for exposure limits recommended or mandated by an organization or vendor. Some exposure limits are set simply to prevent acute effects such as eye or respiratory tract irritation that could make working uncomfortable or difficult to perform. Other exposure limits are set to prevent more serious immediate effects such as death by asphyxia (lack of oxygen). Most exposure limits are set to prevent long-term damage to organs of the body that could occur if high exposures continued over a period of time (days, weeks or even years). There are also exposure limits for shorter time periods and even "instantaneous" exposure limits which further quantify the risk of using a specific chemical.

These consensus values are considered protective of most (but not necessarily all) workers that would be exposed at the specified concentration for up to 8 hours per day, 40 hours per week, for a working life time (which is taken as 40 years). These ratings often are described as the "8-hour time-weighted exposure limit."

In practical terms, a TWA means over the course of the workday there could be periods of time spent working in concentrations above the exposure limit. Those periods would be offset by periods of time spent below the exposure limit. The result would be, that by the end of the workday, the average exposure would be 10 ppm or less.

As a bit of background, the "8-hour time-weighted exposure limit" is estimated to be one-tenth the minimum airborne concentration of vapors to which workers may be repeatedly exposed for an eight-hour workday over a hypothetical career without suffering any possible health effects. All exposure limits are expressed in "parts per million" (ppm). For example, about 18% of the air we breathe is pure oxygen. This means that oxygen is present in the atmosphere at 180,000 parts per million.

Listed below is a comparison of nPB to other commonly used cleaners.

Despite these positive comparisons, users are strongly recommended to design and implement a pro-active safety program for these solvents and for all of the chemicals used in their facilities. MicroCare offers a state-of-the-art product stewardship program which is provided with the solvents at no-charge. In particular, this training should include training about the chemicals, their proper use, issues surrounding flammability, toxicity, skin contact, eye contact and/or accidental ingestion, and safe handling and storage.

Updated: March 23, 2005
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