- Record Type: Interpretation
- Standard Number: 1910.147;1910.147(b);1910.147(c)(1)
- Subject: Interpretation/variance
with the energy isolation device requirements.
- Information Date:1998
January 5, 1998
Mr. Richard J. Hackman
The Proctor & Gamble Company
Ivorydale Technical Center
5299 Spring Grove Avenue
Cincinnati, Ohio 45217-1087
Dear Mr Hackman:
This is in response to your November
8, 1996 letter and enclosure, requesting interpretation/variance
with the energy isolation device requirements of 29 CFR 1910.147.
Please accept our apology for the delay in responding.
In your letter you described a safety
disconnect system ("system") which protects directly wired
load circuits to (functionally interconnected) process machines
from being energized by an electrical source. Also, you stated
that this system is intended for use with process machines
where it is impractical to provide manually-operated disconnects
at every point of access. Further, you disclosed that direct
power interruption on the large drives of these process machines
is infeasible because the disconnects require a significant
effort to operate, are difficult to position in the (production)
line layout, and are not constructed for frequent use.
As noted in your letter, the safety
disconnect system includes the following four basic, component
groups: a power contactor, a control power transformer and
fuses, voltage sensing relays, and a safety lockout switch
with verification light. An optional component is used to
establish a required neutral point for the voltage sensing
relays, if the power being monitored is derived from an ungrounded
The following system safety features
are noted relative to the results of the failure analysis
included in your letter:
The system measures
and ensures no motive force to the drive system.
The system provides
fail-safe verification, that is, defaults to the safe position.
Verification is provided
by a system which actively confirms zero-energy state to the
drives before the verification light comes on.
When an individual
initiates the lockout sequence by opening the system switch
and placing a lock on it, then the verification light will
come on, if the machine is at a zero-energy state.
If the light goes out
due to bulb failure while an authorized employee is performing
servicing and maintenance on the machine, the system remains
safe because the switch is open and locked out.
The system is designed
such that failure of any component in the system will not
result in the light coming on when the machine is in an unsafe
The system is contained
in sealed, protected box.
The equipment used
is certified by a nationally recognized testing laboratory.
An independent laboratory
did a system risk analysis and determined the proposed system
presented the lowest risk to the operator.
Based on the information enclosed
in your letter, your "safety disconnect system" has been evaluated
as an inherently fail-safe system which performs the same
function as an energy isolating device identified in paragraph
1910.147(b). When used as an energy isolating device, this
"safety system" must be addressed in the energy control program
required in §1910.147(c)(1).
Of particular concern is other hazardous
energy sources which are not isolated by the safety disconnect
system. For example, the machine glue heaters are directly
connected (on the supply side of the safety disconnect system)
to the hazardous electrical energy source. Potential employee
exposure to glue heater hazardous electrical and thermal energy
during servicing and maintenance of machines must be addressed
in the energy control program.
We appreciate your interest in employee
safety and health. lf we can be of further assistance, please
contact the Office of Safety Compliance Assistance, Mr. Ronald
J. Davies, telephone (202) 219-8031, extension 110.
John B. Miles, Jr., Director
Directorate of Compliance Programs