Laser Interferometer Gravitational Wave Observatory

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Laser Interferometer Gravitational Wave Observatory

LIGO Laboratory / LIGO Scientific Collaboration

LIGO-E0900042-v4 Advanced LIGO 1 February 2013

Output Mode Cleaner Suspension

Assembly and Installation

Hazard Analysis

Michael Meyer for the SUS team, updated by Jeff Lewis

Distribution of this document:

Advanced LIGO Project

This is an internal working note

of the LIGO Laboratory.

California Institute of Technology

LIGO Project – MS 100-36

1200 E. California Blvd.

Pasadena, CA 91125

Phone (626) 395-2129

Fax (626) 304-9834


Massachusetts Institute of Technology

LIGO Project – NW22-295

185 Albany St

Cambridge, MA 02139

Phone (617) 253-4824

Fax (617) 253-7014


LIGO Hanford Observatory

P.O. Box 1970

Mail Stop S9-02

Richland WA 99352

Phone 509-372-8106

Fax 509-372-8137

LIGO Livingston Observatory

P.O. Box 940

Livingston, LA 70754

Phone 225-686-3100

Fax 225-686-7189


___________________________________ _______________________

John Worden, LHO Site Safety Officer Date


David Nolting, LIGO Lab Safety Officer Date


Brian O’Reilly, Advanced LIGO LLO Installation Lead Date


Michael Landry, Advanced LIGO LHO Installation Lead Date


David Shoemaker, aLIGO Leader Date


Dennis Coyne, LIGO Chief Engineer Date


Albert Lazzarini, LIGO Directorate Date


Date, version, author

Summary of Changes

19 Feb 2009, v1

Michael Meyer

Initial release.

23 Jan 2013, v2

Jeff Lewis

Added Change Log

Revised Related Documents

Deleted hazard “Strain from lifting…” due to the use of the HAM Installation Arm.

Added hazard “Working with wires…”

Revised Hazard Analysis Severity Table

31 Jan 2013, v3

Jeff Lewis

Revised Approval Signature page

Added second paragraph to Section 5.3 Exposure to High Vacuum

1 Feb 2013, v4

Jeff Lewis

Section 2. “…only a directorate review is necessary.” deleted because the mitigated risk level of item #3 reduced from 1E to 3E.

Section 4. Revised Related Documents to current references.

Sections 5.1.1 and 5.3 Deleted version references from document numbers.

Section 6 line 1. Unmitigated risk index changed from 2C to 3C, changed mitigated probability level from “improbable” to “occasional”.

Section 6 line 3. Mitigated probably level changed from 1E to 3E.

Section 6 line 4. Mitigated severity level changed from “minor” to ‘marginal”, changed mitigated probability level from 4E to 3E.

1 Scope

This document covers safety concerns related to the assembly and installation of the Output Mode Cleaner (OMC) suspension into the HAM6 chamber for Advanced LIGO. It must be read before beginning the installation of the OMC.

2Summary of Hazards for OMC Suspension Assembly and Installation

The major hazards to be aware of in the assembly and installation of the OMC suspension include:

  1. Working with wires, including under tension. (4C)

  2. Sudden release of tensioned springs (4D)

  3. Exposure to high vacuum (3E)

  4. Movement of HAM-ISI assembly during installation (4E)

Each hazard is described in detail in section 5.

3Overview of Output Mode Cleaner

The OMC suspension consists of a fused silica optical bench suspended from an aluminum frame. The total weight of the assembly is ~98 lbs with the optical bench accounting for 15 lbs. During the initial assembly of the OMC suspension, the optical bench is replaced with a metal dummy mass to prevent damage to the silica bench. Once the suspension has been assembled and checked, the metal bench is removed and the silica bench is installed. The complete assembly is then moved from its assembly table and installed on the HAM-ISI table inside the HAM6 chamber. The HAM Installation Arm will be used to place the OMC suspension into the HAM6 chamber. A separate Hazard Analysis for the HAM Installation Arm is found at E1000252.

During the assembly and installation of the OMC, it is important that a task leader be assigned to supervise all activities. The task leader needs to be someone experienced with suspensions and their accompanying hardware (OSEMs, blade springs, etc). It is also important that someone with a working knowledge of the OMC optical bench and its attached optics and hardware be involved to supervise any activities related to the bench. The task leader could fill this role as well if they possess the required knowledge.

This assembly and installation requires overall common sense and good lab practices. Personnel must have good working knowledge of how to safely use the tools associated with the build. This work also involves working in the same area as the vacuum system and lasers. All personnel must have appropriate safety training to work at a LIGO facility.

Figure 1. Output Mode Cleaner Assembly

4Related Documents

Output Mode Cleaner Installation Procedures (LIGO-E070271)

Advanced LIGO Safety: Processes and Guidelines (LIGO-M070360)

LIGO Project System Safety Plan (LIGO-M950046)

LIGO Contamination Control Plan (LIGO-E0900047)

LIGO Vacuum Compatibility, Cleaning Methods, and Qualification Procedures (LIGO-E960022)

Advanced LIGO Chamber Entry / Cleaning / Exit Checklist (LIGO-E1201035)

LIGO Hanford Observatory Laser Safety Plan (LIGO-M020131)

LLO Laser Safety Plan (LIGO-M1000228)

BSC Installation Repair Arm and HAM Installation arm Hazard Analysis (E1000252)

5Hazard Analysis

5.1Working with wires, including under tension

The wire used in all of our suspensions is made of spring steel which has stored energy such that it can curl back on itself. It therefore needs careful handling to avoid injury to personnel. In particular, safety glasses must be worn at all times when working with this wire.

5.1.1Wire Sub-Assembly Hazard

Wire segments are cut to desired length, cleaned and then assembled into clamp-wire-clamp assemblies before they are attached to the full OMC assembly. For cutting lengths and cleaning, the detailed procedure given in T1000674, to be included in the assembly documentation, should be followed. This procedure minimizes the chance of a wire end puncturing skin. The key safety points are wearing safety glasses, wearing glove liners as a protective layer, and following a process for cleaning the wire while it is coiled rather than stretching it taut.

The wire segments (called clamp-wire-clamp assemblies) are assembled before they are attached to the full OMC assembly. The wire assembly process requires that they are built under tension in a wire jig assembly. This process provides the possibility that wires could break and spring out of the wire fixture. In addition wire ends might be pointing up during the creation of the wire assemblies. We reiterate that safety glasses must be worn throughout the assembly process.

5.1.2Wire Hazard in full OMC assembly

The fully assembled OMC will have several sets of wires under tension. Safety glasses must be worn at all times when the wires are under tension to prevent injury in the unlikely event that a wire breaks or a wire clamp slips, resulting in the release of a fast moving wire end or shrapnel.

If a laser hazard is present, laser safety glasses may be worn in lieu of regular safety glasses for the purpose of shielding the eyes from wire ends.

5.2Sudden release of tensioned springs

The OMC utilizes several blade springs which are placed under tension during its assembly. The two top springs are each loaded with approximately 11 lbs by the suspended components. In the event that the tension in the springs should suddenly be released, the blade guards on top of the OMC structure, shown in Figure 3, will prevent the springs from traveling upward. The four lower springs have less tension, approximately 4 lbs each, and are similarly guarded from springing upward if a wire breaks. Safety glasses must be worn at all times when the springs are under tension to prevent injury in the unlikely event that a wire breaks or a wire clamp slips, resulting in the release of a fast moving wire end or shrapnel. Laser safety glasses may be worn in lieu of regular safety glasses when a laser hazard is present.

Figure 2. Blade guards over tensioned springs

5.3Exposure to high vacuum

The installation of the OMC will take place in relatively close proximity to the septum plate viewport in the HAM6 chamber. Since the opposite side of the septum plate may be under vacuum, extreme care must be taken to avoid contacting or damaging the viewport during the installation. Care must also be taken to avoid damaging the coating on the viewport, which might impair its function. A viewport cover (LIGO-D080103) must be in place before starting the installation. All vacuum safety procedures must be followed and all personnel must use extreme care when working to prevent damage to the vacuum equipment.

Specifically, prior to entering HAM6 and installing the viewport covers on the septum plate between HAM5 and HAM6, the neighboring volume  (ie HAM5) shall either

be at one atm pressure OR GV1 and GV2 shall be closed so as to limit damage to the vacuum system in case of a catastrophic failure of the viewport. Alternately, the two gate valves isolating the beam tube from the vertex shall be soft or hard closed. In LLO these are designated GV3 and GV5. In LHO these are designated GV5 and GV7. This closure should be confirmed by a member of the vacuum group. Once the OMC is set in place gate valves can be reopened provided the viewport covers are in place when work is being performed in the HAM6

5.4Movement of HAM ISI table

The OMC assembly will be mounted to the HAM ISI optical table. Before the OMC is moved onto the table, personnel need to verify that the HAM ISI has been properly locked down and is not capable of moving. This will prevent any injury to personnel or damage to equipment due to unexpected movement while installing the OMC on the table.

6Output Mode Cleaner Hazard Analysis Severity Table






























































Hazard Risk Index


Risk Code Criteria





1A, 1B, 1C, 2A, 2B, 3A






1D, 2C, 2D, 3B, 3C

Undesirable (Directorate decision required)




1E, 2E, 3D, 3E, 4A, 4B

Acceptable with review by Directorate




4C, 4D, 4E

Acceptable without review


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