Guidelines

General

Acronyms, abbreviations, and initialisms (other than symbols for units of measurement) must be defined the first time they are used in a document or a presentation, and AAIs should not be introduced if they are not used again in the document. Any AAIs defined in an abstract or executive summary should be redefined the first time they are used in the body of the report. Although defining an AAI only one time is usually adequate for the entire document, AAIs may be redefined the first time they are used in each chapter or section, and those reused much further into the document may be redefined to refresh the reader's memory.

AAIs (other than symbols for units of measurement) used in figures and tables should be identified even though they are defined in the text because each figure and table should be self-contained. AAIs should be spelled out in figure captions and table titles (or identified if used more than once in the same figure or table).

When many AAIs are used, it is recommended that a list of AAIs be included in the front matter of a document. Although such a list makes redefining unnecessary in the text, redefining may be helpful to the reader and, as stated above, is recommended in figures and tables.

The use of AAIs is discouraged in document titles and is discouraged but acceptable in text headings. Previously unidentified AAIs in headings should be identified in the text immediately following the heading.

AAIs other than symbols for chemical elements, compounds, and isotopes can begin sentences, as in this sentence.

To avoid confusion, identical AAIs should not be used for more than one entity in the same document (e.g., do not use "NRC" for both Nuclear Regulatory Commission and National Research Council).

Periods

Periods are not used with most AAIs except to avoid confusing AAIs with words (e.g., a period is used with "in.," the abbreviation of the word "inch," to prevent confusion with the preposition "in"). Periods are used with most abbreviations of titles of persons. No space should follow internal periods in AAIs (e.g., A.M., Ph.D.) except following each initial of persons (e.g., C. Jones, C. D. Jones, C. D. E. Jones).

Units of Measurement

Symbols for units of measurement are used only when preceded by a number (e.g., several volts but 6 V). A space is required between the number and the symbol except when used with weapons and ammunition, degrees, percentages, dollars, cents, K for thousand, and M for million (e.g., 22mm ammunition, 15°C, 45° angle, 50%, $500, 4¢, $2K, and $4M). A degree sign is not used with kelvins, and a space is required (e.g., 200 K). The alphabetical lists provide the SI units (American Society for Testing and Materials 1992) for converting many of the English units.

Numbers with symbols for units of measurement used as unit modifiers (compound adjectives) preceding a noun are hyphenated the same as if the unit were spelled out (e.g., 5-m length, 10-cm width, 6-cm-diam hole).

Even though symbols for units of measurement are shown in the alphabetical listings, they do not need to be defined at first or other usage.

Articles

Depending on author/editor preference, traditional usage, and flow, AAIs used as nouns may or may not be preceded with articles "a," "an," or "the" (e.g., NRC or the NRC). The article "a" or "an" preceding a number and abbreviated unit of measurement used as a compound adjective is determined by the sound of the number (e.g., an 11-m pipe, a 12-L capacity). When spoken, units are pronounced in full [e.g., an eleven-meter (not eleven-m) pipe, a twelve-liter (not twelve-L) capacity].

Acronyms and initialisms (remember that they are pronounced as words) used as adjectives may be preceded with articles (e.g., the KATIE project). The choice of indefinite article "a" or "an" is determined by the sound (not the spelling) of the acronym or initialism.

• Acronyms and initialisms that begin with a consonant sound or an aspirated "h" as in heavy should be preceded with "a" (e.g., a LION feature, a HAZWRAP project).
• Acronyms and initialisms that begin with a vowel sound should be preceded with "an" except those beginning with "u" pronounced as in "union," which should be preceded with "a" (e.g., a UNESCO project).

Abbreviations (remember that they are pronounced as letters, not as words) used as adjectives may be preceded with articles (e.g., an NRC guideline). The choice of indefinite article "a" or "an" is determined by the sound of the first letter of the abbreviation.

• Abbreviations that begin with "b," "c," "d," "g," "j," "k," "p," "q," "t," "u," "w," "y," or "z" are preceded with a (e.g., a PBR advantage).
• Abbreviations that begin with "a," "e," "f," "h," "i," "l," "m," "n," "o," "r," "s," or "x" are preceded with an (e.g., an NRC requirement).

Plurals

Plurals of abbreviations with more than one letter and AAIs without periods are formed by adding the lowercase letter "s" (e.g., AAIs, SARs). Plurals of AAIs with periods and single-letter abbreviations are formed by adding an apostrophe and the lowercase letter "s" (e.g., Ph.D.'s, A's). Symbols of units of measurement, however, are not made plural (e.g., 200 V, 100 psi).

Possessives

Possessives of AAIs with or without periods are formed by adding an apostrophe and the lowercase letter "s" (e.g., ORNL's funding).

Hypenation

AAIs combined with one or more words and numbers combined with symbols for units of measurement to form unit modifiers (compound adjectives) preceding a noun are hyphenated as if the AAIs were spelled out (e.g., DOE-funded facilities, 50-km radius, 12-m-long cable, 9-mm-diam hole).

Chemical Elements

The full name of a complex chemical substance should be spelled out the first time it is used unless it is well known.

Chemical elements should be spelled out unless three or more are used together (e.g., uranium and americium or U, Am, and Tc).

Sentences should not begin with symbols for chemical elements (e.g., Uranium, americium, and technetium are used. . . or The U, Am, and Tc contents are measured carefully. . .).

In abbreviated isotopes, superscript mass numbers should precede element symbols (e.g., ²³⁵U not uranium-235).

Proper Names

An abbreviated personal title is usually followed by a period. In our documents, however, social and academic titles are not used in text, references, or lists. In other writing (e.g., correspondence), abbreviations such as "Mr.," "Mrs.," "Ms.," "Prof.," and "Dr." should be used only when they precede proper names (e.g., Mr. Clark, Mrs. Mary S. Jones, or Dr. S. R. Doe).

Abbreviations such as "Rep." and "Sen." should be used only when the given name and last name or initials and last name follow the title (e.g., Sen. John Doe or Sen. J. D. Doe). The title should be spelled out if only the last name is used (e.g., Senator Doe).

Military ranks or rates should be abbreviated only when the given name and last name or initials and last name follow the title (e.g., Gen. James Smith or Gen. J. T. Smith). The rate or rank should be spelled out if only the last name is used (e.g., General Smith).

"Junior" and "Senior" should be abbreviated, preceded with a comma, and followed with a period (and comma if followed by text) (e.g., Jim Brown, Jr., and Joe Black, Sr., are the authors. . . or The authors are Jim Brown, Jr., and Joe Black, Sr.).

Names such as "George," "James," and "William" should not be abbreviated (not Geo., Js., and Wm.).

The names of months should be spelled out in text whether or not they are followed by days of the month (e.g., January 1991 and January 1, 1991); however, they should be abbreviated in bibliographies, lists, figures, footnotes, and tables when the day of the month is included (e.g., Jan. 1, 1991) but must be spelled out if the day is not included (e.g., January 1991). Days of the week should be spelled out in text (e.g., Monday) but may be abbreviated in figures and tables (e.g., Mon.).

In text, most words in proper names of places such as "Avenue," "Center," "Fort," "Road," "Saint," and "Street" should be spelled out (e.g., Fort Lauderdale). In figures, footnotes, and tables, they should be abbreviated (e.g., Ft. Lauderdale).

Directional notations should follow a comma after street names and should be abbreviated without periods (e.g., Grand Avenue, SE; Lincoln Street, NW). Some authorities recommend spelling out cardinal directions (i.e., North, South, East, West) and abbreviating intercardinal directions (i.e., NE, SE, SW, NW).

Country names (for which abbreviations have been established) used as adjectives should be abbreviated (e.g., U.S. industry). Country names used as nouns should be spelled out (e.g., industry in the United States).

State names are spelled out in text. In bibliographies, figures, footnotes, lists, and tables, state names should be abbreviated in the customary way if they follow a city name (e.g., Oak Ridge, Tenn.). In mailing addresses such as those in distribution lists of reports, the two-capital-letter U.S. Postal Service state abbreviations should be used without periods (e.g., Oak Ridge, TN 37831-6285). No comma should precede the ZIP code.

In text, names of establishments should be spelled out or abbreviated exactly as the establishments spell their own names (e.g., Brothers or Bros.). Most words should be spelled out in text (e.g., Company, Corporation, Laboratory), but abbreviations "Inc." and "Ltd." should be used even in text; "Inc." should be preceded with and followed by a comma, but "Ltd." requires no comma (e.g., Lockheed Martin Energy Systems, Inc., is a participant, and Atomic Energy of Canada Ltd. is hosting the conference.).

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