SUBPART P 1926.650
GA Tech Health and Safety
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INTRODUCTION
This training information has been prepared by the Safety and Health Consultation
Program at Georgia Tech with the technical collaboration of Mr. Juán C. Rodriguez and
under the sponsorship of OSHA. Its content may be copied and distributed for free,
and the only request made to the user is that Georgia Tech’s Safety and Health
Consultation Program be acknowledged as the source. All information contained in
this training is believed to be correct by the authors, but it is important to point out
that, this is not an official OSHA publication and has not been revised or approved by
OSHA. The user should be aware that the recommendations provided in this training
do not replace any OSHA standard or regulation.
Georgia Tech Safety and Health Consultation Program
Georgia Tech Research Institute
260 14th Street, Fourth Floor
Atlanta, GA 30332-0837
Voice : (404) 407-7431
FAX : (404) 407-8275
Web http//www.oshainfo.gatech.edu
Email: art.wickman@gtri.gatech.edu
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Definitions
 Cave-in: means the separation of a mass of soil or
rock material from the side of an excavation, or the
loss of soil from under a trench shield or support
system, and its sudden movement into the excavation,
either by falling or sliding, in sufficient quantity so
that it could entrap, bury, or otherwise injure and
immobilize a person
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Definitions
 Competent person:
means one who is capable of
identifying existing and predictable hazards in the
surroundings, or working conditions which are
unsanitary, hazardous, or dangerous to employees, and
who has authorization to take prompt corrective
measures to eliminate them
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Definitions
 Excavation: means any man-made cut, cavity, trench,
or depression in an earth surface, formed by earth
removal
 Hazardous atmosphere: means an atmosphere
which by reason of being explosive, flammable,
poisonous, corrosive, oxidizing, irritating, oxygen
deficient, toxic, or otherwise…
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Definitions
 …harmful, may cause death, illness, or injury
 Ramp: means an inclined walking or working surface
that is used to gain access to one point from another,
and is constructed from earth or from structural
materials such as steel or wood
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Definitions
 Protective system: means a method of protecting
employees from cave-ins, from material that could fall
or roll from an excavation face or into an excavation, or
from the collapse of adjacent structures. Protective
systems include support systems, sloping and
benching systems, shield systems, and other systems
that provide the necessary protection.
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Definitions
 Registered Professional Engineer: means a person
who is registered as a professional engineer in the state
where the work is to be performed. However, a
professional engineer, registered in any state is
deemed to be a "registered professional engineer"
within the meaning of this standard when approving
designs for "manufactured protective systems" or
"tabulated data" to be used in interstate commerce
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Definitions
 Tabulated data: means tables and charts approved by
a registered professional engineer and used to design
and construct a protective system.
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Definitions
 Trench excavation: means a narrow excavation (in
relation to its length) made below the surface of the
ground. In general, the depth is greater than the
width, but the width of a trench (measured at the
bottom) is not greater than 15 feet)
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Definitions
 Means of access and egress: Structural ramps that
are used solely by employees as a means of access or
egress from excavations shall be designed by a
competent person. A stairway, ladder, ramp or other
safe means of egress shall be located in trench
excavations that are 4 feet (1.22 m) or more in depth so
as to require no more than 25 feet (7.62 m) of lateral
travel for employees.
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Definitions
 Soil classification system: means, for the purpose of
this subpart, a method of categorizing soil and rock
deposits in a hierarchy of Stable Rock, Type A, Type B,
and Type C, in decreasing order of stability. The
categories are determined based on an analysis of the
properties and performance characteristics of the
deposits and the characteristics of the deposits and the
environmental conditions of exposure
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Definitions
 Cohesive soil: means clay (fine grained soil), or soil
with a high clay content, which has cohesive strength.
Cohesive soil does not crumble, can be excavated with
vertical sideslopes, and is plastic when moist. Cohesive
soil is hard to break up when dry, and exhibits
significant cohesion when submerged. Cohesive soils
include clayey silt, sandy clay, silty clay, clay and
organic clay
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Definitions
 Stable Rock: means natural solid mineral material that can be
excavated with vertical sides and will remain intact while
exposed
 Type A: means cohesive soils with an unconfined, compressive
strength of 1.5 ton per square foot or greater. Examples of
cohesive soils are: clay, silty clay, sandy clay, clay loam and, in
some cases, silty clay loam and sandy clay loam. Cemented soils
such as caliche and hardpan are also considered Type A.
However, no soil is Type A if: The soil is fissured; or if the soil is
subject to vibration from heavy traffic, pile driving, or similar
effects; or if the soil has been previously disturbed, or if the
material is subject to other factors that would require it to be
classified as a less stable material
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Definitions
 Type B: means:
Cohesive soil with an unconfined
compressive strength greater than 0.5 ton per square foot
but less than 1.5 tsf; or granular cohesionless soils
including: angular gravel (similar to crushed rock), silt, silt
loam, sandy loam and, in some cases, silty clay loam and
sandy clay loam. Likewise, classifies as type A soil,
previously disturbed soils except those which would
otherwise be classed as Type C soil, soil that meets the
unconfined compressive strength or cementation
requirements for Type A, but is fissured or subject to
vibration; or dry rock that is not stable
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Definitions
 Type C: means cohesive soil with an unconfined
compressive strength of 0.5 ton per square foot or less;
or granular soils including gravel, sand, and loamy
sand; or submerged soil or soil from which water is
freely seeping; or submerged rock that is not stable,
and in general any soil about which there is not
reliable information upon its properties
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Definitions
 Unconfined compressive strength: means the load per
unit area at which a soil will fail in compression. It can be
determined by laboratory testing, or estimated in the field
using a pocket penetrometer, by thumb penetration tests,
and other methods.
 Distress: means that the soil is in a condition where a
cave-in is imminent or is likely to occur. Distress is
evidenced by such phenomena as the development of
fissures in the face of or adjacent to an open excavation; the
subsidence of the edge, the slumping of material from the
face, the bulging of material from the bottom of an
excavation, etc
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Acceptable Visual and Manual Tests
 Visual Tests: Visual analysis is conducted to determine
qualitative information regarding the excavation site in general,
the soil adjacent to the excavation, the soil forming the sides of
the open excavation, and the soil taken as samples from
excavated material.
 Observe samples of soil that are excavated and soil in the sides of
the excavation. Estimate the range of particle sizes and the relative
amounts of the particle sizes. Soil that is primarily composed of
fine-grained material is cohesive material. Soil composed primarily
of coarse-grained sand or gravel is granular material
 Observe soil as it is excavated. Soil that remains in clumps when
excavated is cohesive. Soil that breaks up easily and does not stay in
clumps is granular
 Observe the area adjacent to the excavation and the excavation
itself for evidence of existing utility and other underground
structures, and to identify previously disturbed soil
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Pruebas Manuales y Visuales Aceptables
 Pruebas visuales: se realiza un análisis visual para
determinar información cualitativa, relacionada con el
sitio de la excavación en general, el suelo que forma los
lados de la excavación abierta, y las muestras tomadas de
lo extraído
 Observar las muestras de suelo extraído de la excavación y
del suelo a los lados de la misma: tamaño de las partículas:
finas (cohesivo), granulado (no cohesivo)
 Observar el suelo a medida que es excavado: terrones
(cohesivo), si se quiebra o parte fácilmente y no permanece
en terrones (granular)
 Buscar evidencia de conexiones de servicios públicos u otras
estructuras subterráneas (suelo previamente removido)
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Tests...
 Manual Tests: Manual analysis of soil samples is
conducted to determine quantitative as well as
qualitative properties of soil and to provide more
information in order to classify soil properly
 These analyses include tests of plasticity, thumb
penetration, dry strength, and other strength tests
(i.e.; using a pocket penetrometer)
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Maximum Allowable Slopes
 Soil or Rock for excavaciones < 20 feet deep:




maximum allowable slopes (H:V):
Stable Rock ….Vertical (90˚)
Type A…………….3/4 : 1 (53˚)
Type B…………… 1 : 1
(45˚)
Type C………….. 1 ½ : 1 (34˚)
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Design of Sloping...
 The slope may be: “maximum allowable slope”, as
determined from Table B-1 of this appendix and is
expressed as the ratio of horizontal distance to vertical rise
(H : V). Also, it may be “actual slope”, which shall not be
steeper than the maximum allowable slope: (1/2 H: 1V)
 There are special considerations for short term exposure:
means a period of time less than or equal to 24 hours that
an excavation is open
 Sloping or benching for excavations greater than 20 feet
deep shall be designed by a registered professional
engineer
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TRENCH SHIELDS
 Unlike timber shoring for trenches or any other
material which is mainly used as a method of
protection of the integrity of the sides of an
excavation, the use of trench shields (metallic
structures also commonly called “boxes”) is for
protecting the workers from cave-ins and any other
similar incident
 Shields shall be installed in a manner to restrict lateral
or other hazardous movement of the shield in the
event of the application of sudden lateral loads
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Trench Shield...
 Trench shields or “boxes” are generally used in accordance
to the ground slope and the graded bend/edges of the sides
of the trench. The upper edges of the vertical sides (top) of
a “box” shall extend to a height at least 18 inches above the
top of the excavation, except when the sloping of it faces
the opposite side of the “box”
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Trench Shield...
 It may be excavated 2 feet past the lower end of the
trench shield, but only if the “box” has been designed
to withstand the previously calculated force for the
total depth of the trench
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Protection from loose rocks or soil from the
excavation
 Soil and/or any other material excavated shall be
placed at least 2 feet from the edge of the excavation
and/or protective barricades (retaining devices) shall
be installed at intervals on the face of it to stop and
contain falling materials or equipment that could pose
a hazard to employees working in the trench. Also the
excavated material allows for a real measurement of
the trench’s depth
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Loose soil...
 If the materials excavated are not placed at a safe and
appropriate distance from the edges of the excavation,
they may cause changes of the safety requirements
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Workers or vehicles crossing over a trench
 If due to any circumstance, either workers or vehicles
shall circulate/move across a trench then the
following conditions shall be implemented:
 If it is a vehicle crossing over it, a system designed and
supervised by a registered professional engineer shall
be used
 If it is workers walking over it, then a bridge shall be
installed in accordance to the following requirements:
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Crossing over...
 Shall have a safety factor of 4
 Shall have a minimum width of 20 inches
 Shall have a guardrail system installed on both sides in
accordance to the standard
 Shall extend 2 feet beyond the edges of the trench
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Access
 The access to and egress from any excavation shall be
adequate and safe for workers and
following:
require of the
 Trenches more than 4 feet deep shall have some type of
access
 The separation distance between ladders placed in an
excavation shall not be more than 25 feet
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Acceso...
 Las escaleras deben estár aseguradas, y extenderse un
mínimo de 36 pulgadas (.9m) por encima del
borde/orilla superior de la excavación
 las escaleras de metal deben usarse con precaución,
particularmente si hay conexiones de servicios públicos
para electricidad
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Access...
 Ladders shall be secured and the upper ends of their
side rails must extend at least 36 inches above the
surface of the ground / edge of an excavation
 Metal ladders shall be used with caution, particularly if
there are electrical public utility connections
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Location of underground installations
 Keep in mind that there might be underground utility
installations to be encountered during excavation
work , such as sewer, telephone, fuel, electric, water
lines, or any other underground installations. In order
to avoid damaging them as well as a personal safety
measure, their estimated location shall be determined
prior to opening an excavation. Therefore, utility
companies, local government (municipal) offices, or
owners shall be contacted (call up) and asked to
establish the location of the utility underground
installations prior to start digging
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Hazardous atmospheres / confined spaces
 No one shall be allowed to work in hazardous
atmospheres such as:
 Atmospheres containing less than 19.5 percent oxygen
or more than 23.5% of oxygen
 Atmospheres containing a concentration of a
flammable gas in excess of 20 percent of the lower
flammable limit of the gas
 Atmospheres containing concentrations of hazardous
substances and/or atmospheric contaminants which
exceed the safe specified limits indicated by the
government
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Atmospheres...
 All operations which involve these types of atmospheres
shall comply with the requirements specified by OSHA
(Subpart D and E, 29CFR 1926)
 Evaluation/testing of an atmosphere:
 When controls are used that are intended to reduce the level
of atmospheric contaminants to acceptable levels, testing
shall be conducted as often as necessary to ensure that the
atmosphere remains safe before workers go down to the
excavation
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Atmospheres...
 The frequency of the tests shall be incremented in case
that there are operating machinery and equipment,
running-gas motors, welding works, or something shall
be burned in the working area
 In case that the use of proper respiratory protection
shall be necessary, workers shall be trained and
registered in a respiratory protection program
 Some trenches do qualify as confined spaces
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Always take into account :
 HOW MUCH DOES THE SOIL WEIGH?
 EMERGENCY RESCUE EQUIPMENT
 WATER ACCUMULATION
 INSPECTIONS
 BIBLIOGRAPHY
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