ASTM Committee D18 on
Soil and Rock
SI Units In D18 Standards
January 27, 2014
Ron Ebelhar
Richard Ladd
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SI Units Importance
ASTM’s Mission - Be the foremost developer
and provider of voluntary consensus standards with
global recognition and use
ASTM technical committees are urged to give
diligent consideration to the use of rationalized SI
(metric) units in their standards
Critical to the relevance of our standards on the
International level
Monday 01/27/2014
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D18 Activities to Promote Compliance
Long-time commitment to use of SI Units
 One of the first dual-units standards
(D4428/D4428M)
 Standards Preparation Manual guidance
 SI Units – incorporated in D18.91 review

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Unit Systems

There are two basic systems:
Metric and British Inch-Pound

Within these systems there are two approaches:
1.
2.
•
Absolute where mass is the main emphasis (kgm or lbm)
Gravitational where force is the main emphasis (kgf of lbf)
ASTM in the 1980s started to emphasize
through Committee E43 the usage metric
system as it developed into “International
System of Units (SI): The Modern Metric
System”
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SI System
Is mute about the absolute &
gravitational approaches.
 Only follows the absolute approach, but
does give conversion factors for
gravitational units, except for hyl mass
unit & unit weight.
 Frowns upon many units commonly
used by various professions: such as
doctors & civil engineers.

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ASCE Civil Engineering Mag.
November 2013
From Article on cruse ship Costa Concordia, Pg. 28
“An Italian-American consortium”:
“By noon an estimated pulling force of
6 million kgf exerted by the strand
jacks operating a system of winches and
steel chains had produced a “smooth
rotation movement of the hull, ____.”
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Inch-Pound System
ASTM is mute on both the absolute &
gravitational approaches in standards.
 Can a standard use both approaches
within a standard; that is use lbf and
lbm?
 Committee D18’s solution: This work
shop and the usage of D18 Standards
Preparation Manual and D18.91’s
Special Memorandums.

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Justification for D18 Standards Preparation Manual
(D18 SPM)
and Subcommittee D18.91 Special Memos


On UNITS
H1.1 States “This part is intended to guide technical committee in the use
of the standard formats for denoting the use of the International System of
Units (SI), non-SI units (usually inch-pound), or both in ASTM standards.”
D18 interprets this to mean other formats then those presented in H3
and H4 are acceptable, because the term “guide” instead of “shall or
should” is used.
For example, to make D18 Standards more user friendly:
a) In a combined standard, inch-pound units can be presented
before SI units, especially when the apparatus was developed in
inch-pound units.
b) In a SI standard, non-rationalized inch-pound units can be given
for information only in parentheses.
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On UNITS (continued)




H1.2.2.1 States “For committees that have special considerations with the
use of SI units in ASTM Standards, it is permissible to develop committee
specific technical guidance for clarification.”
D18 interprets this to mean we can give guidance on SI and inchpounds units that are specific to the professions represented within
D18’s Scope.
For example, civil engineering uses “unit weight or force per volume”
in many applications/standards. The units being lbf/ft3 or kN/m3.
Such units are presented in D18 SPM and contained in many D18
Standards.
Density units of g/cm3 are frequently used in D18 Standards, where as
IEEE/ASTM SI 10 states they should be avoided.
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On UNITS (continued)



Omission Problems:
The “Blue Book”, IEEE/ASTM SI 10-2010, and NIST Guide for the
Use of the International System of Units (SI) documents do not
mention/present the fact that there are other components or
approaches involved in metric and inch-pound (IP) system of units.
That is absolute and gravitational, whereas SI 10-2010 & NIST Guide
present many conversion factors for gravitational metric and IP
units to SI; such as: kgf to kN and lbf to kN.
Furthermore, conversion factors are given for absolute IP units to SI
units, such as lb to kg (note the notation for mass is not given).
It should be noted that cgs units are mentioned, “they should be
avoided!” Another good one is: doctors and emergency medical
services should not use blood pressure in mm Hg but Pa (can you
imagine the response to “his blood pressure is 19,000 Pa”).
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On UNITS & Omission Problems
(continued):
The “Blue Book” in Part H does not mention
what approach (absolute/gravitational) to inchpound is preferred. In addition, can those two
approaches be used in a given standard?
 To cover these omission problems, D18 is
presenting this workshop and will revise the
D18 SPM based on the results of the workshop
and presentations to its Executive
Subcommittee D18.90.

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Highlights of D18’s Policy or
Recommendations on Units
If force is mentioned in the standard and inchpound (IP) units are included, then the
gravitational inch-pound (IP) system shall be
used. That is force is represented by lbf (IP)
and N (SI).
 If force and mass/density are included in the
standard, then only SI units are used for
mass and density and the combined units is
the preferred presentation (ST & [IP] or IP &
[SI]).
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
Policy or Recommendations, cont.
For standards where the apparatus was
developed using the IP system of units, the
D18 SPM has specialized guidance for the
presentation of IP and SI units.
 If the standard's "Calculation" section is
complicated/extensive, only one set of units
should be used; typically SI if density is
involved.

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Policy or Recommendations, cont.

The unit section within the "Scope" should define
in detail how units are being used. The D18 SPM
presents five (5) typical formats, where as the
"Blue Book" presents three (3).
 The Civil Engineering Profession for over a
century has used some units not covered or
frowned upon by the SI standard; therefore it is
D18's policy to continue to represent this
profession by using such units as unit weight
(lbf/ft3), density in g/cm3 or Mg/m3, and dimension
in cm.
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Policy or Recommendations, cont.


D18 is committed to develop standards that are
within its scope and services the “users,” both
domestic and foreign.
To meet this commitment are standards should
use combined rationalized units as applicable.
 Cover new approach of rationalized units for
apparatus
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Rationalized Units for Apparatus Developed in
Inch-Pound Units


The SI converted numbers should have the
same/similar number of significant digits as the
inch-pound units.
The apparatus description section or figure, or both
contain the following type of statement/note; "The
SI units presented are basically hard conversions
of the inch-pound units, other rationalized SI units
should be acceptable providing they meet the
requirements established by the inch-pound
apparatus."
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Rationalized Units cont.

The addition, the following note could be
beneficial: Note X—The Subcommittee (insert
number) is seeking details covering apparatus
specifications using rationalized SI units. Send
such details to the D18 Staff Manager at ASTM
International (www.astm.org or address given in
every standard).

Present slides on Dispersion Cup
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Uncorrected Version of Dispersion Cup
Corrected Version of Dispersion Cup
Note X—The subcommittee
(insert number) is seeking
details
covering
apparatus
specifications using rationalized
SI units. Send such details to the
D18 Staff Manager at ASTM
International (www.astm.org or
address
given
in
every
standard).
QUESTIONS ?

ASTM web site – www.astm.org
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