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U. S. Department of Labor
Occupational Safety and Health Administration
Directorate of Science, Technology and Medicine
Office of Science and Technology Assessment
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Hazard of Potential Sidewalk Grate System Failure
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Safety and Health Information Bulletins |
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SHIB 12-30-2004 |
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This Safety and Health Information Bulletin is not a standard or regulation, and
it creates no new legal obligations. The Bulletin is advisory in nature,
informational in content, and is intended to assist employers in providing a
safe and healthful workplace. Pursuant to the Occupational Safety and Health
Act, employers must comply with hazard-specific safety and health standards
promulgated by OSHA or by a state with an OSHA-approved state plan. In addition,
pursuant to Section 5(a)(1), the General Duty Clause of the Act, employers must
provide their employees with a workplace free from recognized hazards likely to
cause death or serious physical harm. Employers can be cited for violating the
General Duty Clause if there is a recognized hazard and they do not take
reasonable steps to prevent or abate the hazard. However, failure to implement
any recommendations in this Safety and Health Information Bulletin is not, in
itself, a violation of the General Duty Clause. Citations can only be based on
standards, regulations, and the General Duty Clause. |
Preface
Many sidewalks and roadways near large urban buildings incorporate
surface grate systems to cover vaults and pits. In heavy snowstorms, snow
accumulates on the grates. During a snowstorm in 2003, a skid-steer loader being
used to clear sidewalk snow fell into a vault when the grate system failed under
the weight of the loader, fatally injuring the operator.
Purpose
The purpose of this Safety and Health Information Bulletin (SHIB) is to:
- Alert employers and employees who use skid- steer
loaders and other heavy machinery to clear snow or debris from grate systems
over pits and vaults that:
- They must determine whether local building codes permit heavy machinery to
be operated on sidewalks and over grate systems;
- These grate systems may fail under the weight of the loaders/machinery;
- Remind employers that OSHA standards for Walking-Working Surfaces that
address floor opening covers and their supports require that they meet
standard strength and construction requirements; and
- Recommend that all such surface grate systems be inspected regularly and
remind employers that steps must be taken to ensure that these grate systems
have the capacity to support the weight of heavy machinery, unless procedures
are implemented to effectively prevent the operation of heavy machinery on
such grates.
Background
The Occupational Safety and Health Administration's (OSHA's) Braintree,
Massachusetts Area Office investigated a fatal accident where a skid-steer
loader used to clear snow from sidewalks plunged into a vault when a metal grate
(Figure 1) covering the vault failed.
Accident Description
The accident occurred at a large hospital in the Boston metropolitan area. Many
of the sidewalks and roadways on the hospital grounds have grates built flush
with the surface to cover vaults or pits. In heavy snowstorms, snow accumulates
on the grates. The hospital uses two skid-steer loaders to clear snow from
roadways and sidewalks. The grates involved in this accident were made of
aluminum and were bolted onto steel angle iron that was bolted into the concrete
of the sidewalk vault. At the time of the accident, the age of the grates and
their load capacities were unknown. The engineering drawings for the grate that
were found after the accident did not reflect the conditions of the grate system
as it was built.
Different crew members drove the skid-steer loader over the grate on the evening
of the accident. When the victim drove over the grate, the grate system failed.
The bolts attaching the angle iron to the concrete later were found to be
corroded. The load caused the bolts to fail, pulling the angle iron away from
the concrete and permitting the grates and the skid-steer loader to drop
approximately 20 feet
(Figures 2 & 3). The employee died about an hour after the accident.
Figure 1.
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Figure 2.
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Figure 3.
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OSHA's Walking-Working Surfaces Standards
29 CFR 1910.21(a)(2) defines Floor Opening as "an opening measuring 12
inches or more in its least dimension, in any floor, platform, pavement, or yard
through which persons may fall; such as a hatch- way, stair or ladder opening,
pit, or large manhole."
29 CFR 1910.22(c) requires that "Covers and/or guardrails shall be provided to
protect personnel from the hazards of open pits, tanks, vats, ditches, etc."
29 CFR 1910.23(a)(5) requires that "Every pit and trapdoor floor opening,
infrequently used, shall be guarded by a floor opening cover of standard
strength and construction."
29 CFR 1910.23(e)(7)(i) requires that "Trench or conduit covers and their
supports, when located in plant roadways, shall be designed to carry a truck
rear-axle load of at least 20,000 pounds."
29 CFR 1910.23(e)(7)(iii) requires that "The construction of floor opening
covers may be of any material that meets the strength requirements."
Other Information
Consultation with municipal public works departments has revealed that some
municipalities may not have specific building code provisions that address the
capability of existing sidewalk grate systems to support concentrated loads. In
addition, there also may not be specific regulations prohibiting the use of
heavy equipment on sidewalks.
One municipality indicated that, for new construction of sidewalk grate systems
over which heavy equipment may be operated, it requires that the grate system's
building plan reflect that the grate systems are able to support concentrated
truck loads with load capacity certifications provided by a professional
structural engineer.
Conclusion
Employers are required to comply with applicable OSHA standards. In addition,
employers must determine whether local building codes allow heavy equipment to
be operated on sidewalks and, if so, whether grate systems comply with building
code provisions relating to grate system design and support capability.
In general, sidewalk grates are designed and constructed for pedestrian use and
are not built with redundant supports, which are essential when heavy equipment
is operated on sidewalk grate systems
The support system for the sidewalk grate at the Boston-area hospital was not
built with redundant supporting mechanisms and the entire grate system was not
designed for the concentrated load of heavy equipment such as skid-steer
loaders, forklifts or other vehicles. The steel and concrete interface was
subject to corrosion from weather and salt. The bolts that anchored the angle
iron into the concrete wall were
not visible during regular inspections, so the extent of the corrosion could not
be detected.
Employees who drive equipment with concentrated loads on wheels (skid-steer
loaders, forklifts or other heavy equipment) on sidewalks or roadways with flush
surface grates are exposed to a potential hazard. In this accident, the employer
performed regular maintenance checks of the sidewalk grate and support system.
However, the areas subject to corrosion were not visible during inspections.
The employer installed a new grate system with sufficient capacity to support
heavy equipment
(Figure 4) after the accident.
Figure 4.
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Methods to Address the Hazards
In addition to complying with applicable OSHA standards and local building codes
relevant to sidewalk grate systems, employers can significantly reduce the
likelihood of a grate system failure by taking the following steps:
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Develop and communicate written policies regarding snowplowing or operating
machinery on top of grates.
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Ensure that all operators of heavy machinery that can access sidewalks or
roadways,
know the weight of the machines that they are operating, the locations of the
grates, and the load capacities of the grates.
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Inventory all sidewalk and roadway grates on site and perform regular
engineering inspections to determine the condition and load allowances of all
grates.
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Consult with engineers regarding redundant support structures for new and
existing grate systems.
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Ensure that all engineering drawings for grate systems are current and
reflect the conditions of the grate systems as they were built.
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When building new vaults, consult with a professional structural engineer in
designing a concrete shelf system for the angle irons to rest on and be bolted
onto, and certify the load capacity of the grate system.
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