Preventing Injuries And Deaths From Metal-Reinforced Hydraulic Hoses
NIOSH of the US
has warned that workers may be burned or electrocuted when using metal
reinforced hoses on aerial bucket trucks near energized power lines. It said
reports of one fatality indicate that metal reinforced hydraulic hoses may
rupture and cause fires if they contact energized power lines. Electric current
flowing through the metal reinforcement may also create an electrocution hazard.
The Occupational Safety and Health Administration
(OSHA) requires the use of nonconducting hydraulic hoses near energized power
lines. The recommendations in this alert are for the attention of utility
companies, electrical contractors, manufacturers of aerial bucket trucks and
hydraulic impact tools, insurers of these companies, electrical linemen and
maintenance personnel.
Case
report
A 37-year-old electrical lineman who worked for a
contractor died when he jumped from a burning aerial bucket and fell 35 feet to
the ground. When the fatal accident occurred, he was sagging (adjusting slack
in) the center phase of a three-phase, 12,400-volt, energized power line. A
metal reinforced, rubber hydraulic hose was attached to an impact wrench the
lineman was using. When the hose simultaneously contacted two phases of the
power line, the heat generated by the electric current in the metal
reinforcement caused the hose to melt and rupture.
When the hydraulic fluid from the ruptured hose
contacted the power line, the fluid ignited and the aerial bucket became
engulfed in flames. As the fluid continued to spray onto the power line, the
fire intensified. The lineman rotated the aerial bucket away from the power line
until the bucket controls stopped functioning. He then attempted to jump to an
earthen bank about 15 feet from the side of the bucket but he caught his foot on
the bucket lip and fell to the ground, landing on his head and chest.
A field mechanic had installed the metal reinforced
hose five months before the fatal accident. During later interviews, the
mechanic said he knew he was installing the wrong type of hose but did not
understand the hazards involved.
Following the accident, the electrical contractor
inspected the hydraulic hoses on all of his aerial buckets and found no other
metal reinforced hoses. However, when the local utility company inspected their
aerial bucket trucks, they found several metal reinforced hydraulic hoses on
booms or aerial buckets that might be used near energized power lines.
Conclusions
As the case reported here shows,
electrical contact between two power line phases through a metal reinforced
hydraulic hose can generate sufficient heat top rupture the hose and cause a
fire. In addition, en electrocution hazard can be created if a metal reinforced
hose on the boom of a truck contacts an energized power line and allows current
to flow through the truck chassis.
NIOSH recommends that the following precautions be
taken to control hazards associated with hydraulic houses used on aerial bucket
trucks:
- Employers should not install metal reinforced
hydraulic hoses on any part of the boom, aerial bucket or hydraulic
attachments of aerial bucket trucks near energized power lines
- Employers should remove metal reinforced hoses
installed on any part of the boom, aerial bucket or hydraulic attachments of
aerial bucket trucks used to work near energized power lines
- Before work begins, employers should require a
competent person to conduct initial and daily jobsite survey and inspect all
equipment to identify hazards and implement controls
- Employers should stress the importance of
adherence to safe work procedures including covering energized power lines in
the work area with insulating hoses or blankets or de-energising and grounding
the lines before work begins.
- Employers should provide all workers with training
that shows how each step controls the hazard. For e.g., the field mechanic in
the case reported here knew he was installing the wrong type of hose but he
did not know about the fire or electrocution hazard associated with using a
metal reinforced hose near energized power lines.
- Employers should install all hydraulic hoses used
in aerial buckets so that the flow of hydraulic fluid can be stopped
immediately by the worker in the bucket. This can be achieved by incorporating
a control valve into the hydraulic system in the aerial
bucket.
- Employers should encourage equipment and tool
makers to design an independent coupling system to prevent the use of
unsuitable hydraulic hoses on booms, aerial buckets or aerial bucket
attachments. Labeling or color coding hoses may also help workers who service
this equipment.
Source: DHHS (NIOSH) Publication No. 93-105
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