NATIONAL CRANE
Published 11-01-2020 Control # 710-00
2-5
NBT60XL OPERATOR MANUAL
SAFETY PRECAUTIONS
2
Anti-Two-Blocking Device
This equipment should have a functional Anti-Two-Block and
Control Lock-Out System. Test daily for proper operation.
Two-blocking occurs when the load block (hook block,
downhaul weight, rigging, etc.) comes into physical contact
with the boom (boom nose, sheaves, jib, etc.). Two-blocking
can cause hoist rope (wire rope or synthetic rope), rigging,
reeving, and other components to become highly stressed
and overloaded, in which case the rope may fail allowing the
load, block, etc. to fall.
Two-blocking is more likely to occur when both the main and
auxiliary hoist lines are reeved over the main boom nose and
jib nose, respectively. An operator, concentrating on the
specific line being used, may telescope or lower the boom
allowing the other hoist line attachment to contact the boom
or jib nose, thus causing damage to the sheaves, or causing
the hoist rope to fail, dropping the lifting device to the ground
and possibly injuring personnel working below.
Caution must be used when lowering the boom, extending
the boom or hoisting up. Let out load line(s) simultaneously
to prevent two-blocking the boom tip(s) and the hook block,
etc. The closer the load is carried to the boom nose the more
important it becomes to simultaneously let out hoist rope as
the boom is lowered. Keep load handling devices a minimum
of 107 cm (42 in) below the boom nose at all times.
Two-blocking can be prevented. Operator awareness of the
hazards of two-blocking is the most important factor in
preventing this condition. An Anti-Two-Block System is
intended to assist the operator in preventing dangerous two-
block conditions. It is not a replacement for operator
awareness and competence.
Never interfere with the proper functioning of operational
aids or warning devices.
Working Area Limiter (If Equipped)
This equipment may be equipped with a working area limiter
as part of the RCL system, designated as either Work Area
Definition System (WADS) or Working Range Limiter (WRL).
You must read and understand the operator manual before
operating the working area limiter system. Become familiar
with all proper operating procedures and with the
identification of symbol usage.
The working area limiter is intended to be used as an aid to
the operator. It is not a substitute for safe equipment
operating practices, experience and good operator
judgments.
EQUIPMENT STABILITY/STRUCTURAL
STRENGTH
To avoid death or serious injury, make sure that the
equipment is on a firm surface with load and equipment
configuration within capacity, as shown on the equipment’s
Load Chart
and notes.
Make sure that all pins and floats are properly installed and
outrigger beams are properly extended before lifting on
outriggers. On models equipped with outriggers that can be
pinned at the mid-extend position (vertical stripe, if
applicable), the outriggers must also be pinned when
operating from the mid-extend position.
Use adequate cribbing under outrigger floats to distribute
weight over a greater area. Check frequently for settling.
Read and follow the following safety decal for equipment
with a single front outrigger.
9250
Example decal. For reference only.
Fo
r
Reference
Only
