E-stop and stored energy release

[gusto34]

I am investigating a situation where a maintenance worker was injured during a non-routine repair procedure. The injury resulted from the release of stored energy after the Emergency Stop (E-Stop) was activated prior to maintenance. The relase was obviously unepected by the maintenance worker, and occured after the main pneumatic feed to the machine had been bled down. The stored energy was internal to the machine and was unaffected by the E-stop or the bleed down. Release of internal energy storage required jogging the machine, and this was not done.

My question now is if the E-Stop process should have removed ALL of the potential hazards to maintenance, including the release of ALL of the stored energy, or must the E-stop only remove harzards related to normal machine operation without concern for non-routine maintenance.

I understand that various industry codes such as NFPA 79 and ANSI B20 require that an E-Stop release stored energy that can create a hazard. And OSHA 1910.147 covers the lockout / tagout process with mention of releasing any residual energy prior to maintenance. I don't see where this OSHA document references an E-Stop in particular.

I will apprecate any comments on any "official" requirement for an E-Stop to remove ALL hazards verses a lesser requirement to remove only the hazards to a normal operator.

Thanks.

 

[humanfactoreng123]

See the following OSHA Letter that shows the interpretation of the 29CFR1910.179 (1)(2)(c) emergency switches:

July 1, 1982

Keith C. Hatsell, P.E.
Director of Engineering
Shepard Niles Crane & Hoist Corporation
Montour Falls, New York 14865


Dear Mr. Hatsell:

This is in response to your letter of June 9, 1982, requesting an interpretation of 29 CFR 1910.179(l)(2)(c). Your letter addressed to Mr. Chester C. Whiteside was forwarded to this office for our interpretation.

It is OSHA's position that the main or emergency switches mentioned in 29 CFR 1910.179(l)(2)(c) must be capable of being locked out. The subject standard does not require two different switches. However, the switches are defined below for your information:

29 CFR 1910.179(a)(59) defines "emergency stop switch" as a manually or automatically operated electric switch to cut off electric power independently of the regular operating controls.

29 CFR 1910.179(a)(61) defines "main switch" as a switch controlling the entire power supply to the crane.

We concur with your interpretations that the pendant push button unit which operates the crane bridge motions does not fall into the category of a main or emergency switch; and the pendant push button units which operate the crane motions do not, currently, include a switch that can be locked out in the open position as a standard feature.

If we may be of further assistance, please contact us.

Sincerely,



Patrick R. Tyson
Director,
Federal Compliance and State Programs


--------------------------------------------------------------------------------



JOHN HEYWOOD, P.E., CSP
SENIOR SAFETY ENGINEER
Saint Louis, Missouri 63125

 

[conduit]

Hi,

It is important to remember that an e-stop function is to
prevent damage to equipment or personnel that is operating equipment during normal operations. Non-routine work requires compliance with the LO/TO standard. E-stop as a rule should be use to bring the machine to a complete stop as soon as possible. If the e-stop is working correctly, the machine cannot be started again unless e-stop has been reset.E-stop is not ment to take care of all potential energy that may be stored in a machine.

 

[castera]

An E-stop is generally used to bring a machine to a halt as quickly as possible and is not intended to provide a full isolation and immobilisation from all sources of energy.
An E-Stop cannot be expected to remove all sources of energy as this may not be the safe thing to do in every foreseeable circumstance, in fact removing all sources of energy may require continued motion - consider a crane hoist lowering a load, the crane driver sees a hazard and so presses the E-stop. The hoist should stop as quick as safely possible. The load would still be suspended on the hook and hence stored energy remains in the hoist system. If maintenance work where required at this point a risk assessment should highlight the fact that stored energy remains in the system and the steps taken to render the stored energy safe before work commences. The same would also be true of hydraulic and pnumatiic systems. Generally for all foreseeable circustances it is best to stop machinary and hold any stored energy systems in their last state if the removal of the stored energy would involve continued motion.

 

[afterhrs]

Gusto 34,
During non-routine maintenance the machine must be locked out, and all stored energy released, in accordance with the COMPANY generated lock out procedure per OSHA. It is the responsability of the COMPANY to generate and train all affected employees on this procedure, per OSHA.
An emergency stop should ideally be used to prevent
potential harm to individuals and equipment damage.

Regards,
Afterhrs

 

[safetydan]

One thing to remember about an E-stop and LO/TO is that an E-stop is not an energy isolating device. An E-stop in it's very nature is a switch which is used to quickly turn a peice of equipment off in order to prevent damage to the equipment. It will not isolate energy from reaccumulating, or prevent someone from simply resetting the E-stop.

Any non-routine maintenance must be performed under LOTO as per OSHA reg whenever the technician enters an area of operation where accidental startup may occur.