U. S. Department of Labor
Occupational Safety and Health Administration
Key Switch Controlled Elevating and Rotating Aerial
Lifts
Technical Information Bulletin
TIB 02-04-11
The Occupational Safety and Health Administration's (OSHA's) Directorate of
Technical Support issues Technical Information Bulletins (TIBs) to provide
information about occupational hazards and/or to provide information about
noteworthy, innovative, or specialized procedures, practices, and research that
relate to occupational safety and health. These bulletins are not standards or
regulations and create no independent legal obligations. They are advisory in
nature, informational in content, and are intended to assist employers in
providing a safe and healthful workplace.
Further information about this bulletin may be obtained by contacting OSHA's
Directorate of Technical Support at 202-693-2095.
Purpose
The purpose of this Technical Information Bulletin is:
To inform users of subject aerial lifts that emergency rescue of
employees on the lifts can be delayed if:
the upper and lower controls used to operate the lift are selected by
key;
the key can be removed while set in the upper, off, or lower
position; and
the key is removed from the switch and not immediately
available to individuals on the ground;
To alert users that the subject lifts should only be operated when the
operational mode switch key is inserted in the switch, unless the key is
otherwise readily available and immediately accessible for use; and
To provide recommendations for employers that own the subject aerial
lifts.
Background The Hartford Area Office brought to the attention
of the Directorate of Technical Support an accident that it investigated
involving an elevated aerial lift with a keyed mode selector. The accident
occurred when an employee was working on an electrical panel with the basket
elevated about 20-25 feet off the ground. When an electric arc from the
electrical panel ignited the employee's clothing, he was only able to lower the
basket to a height about 12 feet above the ground before he became
incapacitated. Co-workers tried to lower the aerial lift further, but could not
operate the lower controls because the control key had been removed and was not
available to them.
Description of Hazard
The subject aerial lifts have two sets of controls that can be used to move the
boom and the basket. One set of controls is located in the basket at the end of
the telescopic boom. A second set of controls is located in a panel mounted on
the lower superstructure of the lift, which is mounted on the chassis of the
lift.
On the lift involved in the accident, the keyed switch controlling the lower and
upper sets of controls works as follows: Prior to starting the engine, the
emergency stop button must be pulled out, and the key turned to the right or
left depending on the desired operating mode. One mode is for the basket level
operation (upper controls). The other mode is for ground level operation (lower
controls). Once the control mode is set, a momentary contact switch is
activated. The lift can then be operated from either the basket or ground level,
depending upon the mode selected.
During the attempted rescue of the injured worker, the basket could not be
lowered to the ground with the lower controls. The lower controls were
inoperative because the switch was locked in the upper controls position, and
the key for the operational mode switch was not in the switch. In that
position, the lift can only be controlled from the upper controls in the aerial
basket. The switching mechanism can not be switched to the lower controls
without the key; thus, the lower controls could not be used to override the
upper controls, and the individuals on the ground were unable to readily assist
the incapacitated employee.
Other Information
While many aerial lifts are equipped with a key mode switch that only allows the
key to be removed from the switch panel when the key is in the "OFF"
position and the lift is locked in a lowered position, some aerial lift models
are manufactured such that the key may be removed from the key mode switch at
any time. If an aerial lift's design permits individuals to remove the key from
the key mode switch at any time, and the aerial lift is not equipped with an
alternative device to lower the basket from the ground in emergencies (e.g., an
emergency-lowering-piston that can be operated independently of the mode switch,
permitting the basket to be lowered in an emergency by a separate control
lever)1, employees working from the basket may be at risk unless
the key remains in the key mode switch or the employer can assure that, at all
times when the aerial lift is being used, the key or a duplicate key, is in the
possession of a person who is readily available and immediately accessible to
the aerial lift.
OSHA's 29 CFR 1910.67(c)(2)(ix) standard for general industry and OSHA's
29 CFR
1926.453(b)(2)(ix) standard for construction, require aerials lifts to
"have both platform (upper) and lower controls. Upper controls shall be in
or beside the platform within easy reach of the operator. Lower controls shall
provide for overriding the upper controls. Controls shall be plainly marked as
to their function. Lower controls shall not be operated unless permission has
been obtained from the employee in the lift, except in the case of
emergency."
The American National Standards Institute (ANSI) standard A 92.2-1990, Vehicle-Mounted Elevating and Rotating Aerial Devices, Section 4.3.3 contains
the following requirements for the lower Controls: "Lower controls shall be
readily accessible and shall provide for over-riding the boom positioning upper
controls provided the upper control system is intact. They shall be plainly
identified as to their function and protected from damage and inadvertent
actuation."
A92.5-1992, Boom-Supported Elevating Work Platforms, Section 4.10.2 requires
"Lower controls shall be readily accessible from ground level and shall: a)
Override upper controls for powered functions. b) Be provided for all powered
functions except drive and steering. c) Be of the type that automatically
returns to the "off" or "neutral" position when
released if used to control any movement of the aerial platform. d) Be protected
against inadvertent operation. e) Be clearly marked."
Conclusions
When the subject lifts are operated from the basket and
they required to switch operation to the lower controls is removed, potential
rescuers may have difficulty reaching an injured or incapacitated employee who
is unable to operate the basket controls, unless the rescuers can immediately
locate the key and lower the injured or incapacitated employee using the lower
controls.
The subject aerial lifts' lower controls have the capability to override the
upper controls only if the key is in the lower controls mode. In order for such
lifts to meet the requirements of the OSHA and ANSI standards, it is essential
that: (1) the key remains in the key switch, so that it can be set to activate
the lower controls, and can provide a means to lower the platform, or (2) the
key, or a duplicate key, is in the possession of a person who is readily
available and immediately accessible to the aerial lift, so that in an
emergency, the lower controls can be used to override the upper controls and
lower the aerial lift.
Recommendations
Aerial lifts used in general industry on in
construction activities must meet the requirements of 29 CFR 1910.67 or
29
CFR 1926.453 standards respectively. The lower controls of the subject lifts
must be able to override the upper controls in an emergency. Thus, when
employees are working from the basket on the subject lifts, the key must not
be removed from the switch control panel when the setting is in the
upper control position, unless the key or a duplicate key, is in possession
of a person who is readily available and immediately accessible to the
aerial lift.
1 The European mobile elevating work platforms (MEWPs)
standard, EN280, requires the MEWPs be fitted with an over-riding emergency
system, e.g., a hand pump, secondary power unit, or an emergency-lowering-piston
that can be operated independently of the mode switch, permitting the basket to
be lowered in the event of an emergency by a separate control lever. The EN280
standard also allows the lower controls be used as the emergency device. Section
4.10.4 of ANSI A 92.5-1992 standard requires that "All aerial platforms
shall be provided with an auxiliary means of lowering, retracting, and rotating
in the event of a power loss."
