indico.cern.ch · Web viewThe PMT block is an iron cylinder itself inserted into an aluminium body. The aluminum body contains up to 12 PMT blocks. The aluminium body is encased in

Safety Derogation Request Form

Date : 25. 06. 2019 Requested by : Christophe Clément ([email protected]) Dept/Group : EP/ATLAS

DESCRIPTION OF THE REQUEST

Location / Project : UX15 – ATLAS Tile Calorimeter, inside module (girder), inside PMT Block, HV Divider (see attached drawings & photos) / ATLAS Tile Calorimeter Phase-II Upgrade

Regulation related to the derogation: ( state the regulation(s) which is/are not being respected)

IS23 Rev. 3 page 1: ”Note: The requirements of low smoke density, low toxicity and corrosivity of gases from fires exclude some very commonly available materials such as polyvinyl chloride (PVC), chlorosulphonated polyethylene (Hypalon®), polychloroprene (Neoprene ®), fluorocarbons (e.g. Teflon®) and other halogenated or sulphur containing Compounds”.IS41 Rev. 1 page 17: ”2.5.14 Polytetrafluorethylene (PTFE) Although PTFE (Teflon®) only melts and decomposes at temperatures exceeding 500˚C, it emits, under these conditions, highly toxic and corrosive smoke containing hydrogen fluoride and highly toxic fluorides of carbon. Although it is a very useful material with unique properties its large scale use should be avoided also because of its very poor radiation resistance.”

Gap compared with the reference regulation

concerns a technical aspect concerns an organisational aspect concerns a financial aspect

Description of the gap: Usage of LAPP Cable, RG 188 A/U, with base material PTFE (Teflon)

Cause of the gap : The ATLAS TileCal PMT block geometry constrains physical properties of the proposed cable: diameter and flexibility of the cable. The requested cable is placed in a confined space inside the ATLAS TileCal PMT block which is an iron cylinder. The PMT block geometry is defined by the existing legacy ATLAS Tile calorimeter that is going to be kept for the LHC high luminosity upgrade. Electrical properties are defined by the Tile calorimeter high voltage system. The legacy Tile calorimeter geometry requires the usage of small diameter and flexible cable so that they can fit inside the existing PMT blocks. Another important requirement on the proposed cable is that it must allow soldering on the circuit board which has a very limited size. The small size of the board forces us to solder the cable to the board. The soldering process requires that the plastic material inside the cable be compatible with the soldering temperature.

Please note: The proposed cable with the Teflon material is confined in small quantities inside the Tile calorimeter PMT blocks (see Figure 1). Each PMT block contains 1.564 g of Teflon inside the proposed cable. The PMT block is an iron cylinder itself inserted into an aluminium body. The aluminum body contains up to 12 PMT blocks. The aluminium body is encased in an hermetic steel body over a total of 256 modules. So each steel box contains a total of 68.816 g of Teflon, but spread among encased 12 PMT

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blocks (see Figure 2).In terms of mass the cables represent in total 16kg (1.564g/PMT Block; max.68.816g/module) and in terms of length 1742 m (0.17m/PMT Block; max 7.5m/module).

Further comments:Fire Risk: Ignition sources may be short cuts or electric sparks Drips are negligible as the material is contained inside the metallic PMT Block and girder (steel) sealed with iron plates

Mitigation: 1) The proposed cable is encased in small quantities in an iron cylinder (PMT block) itself inserted inside an aluminium body, itself inserted inside a steel box and separated from the other modules. 2) The Tile Calorimeter will be equipped with a sniffer system to detect smoke inside the metal box. 3) In case of smoke detection the power to the HV and LV system is cut immediately at the level of the counting room racks. 4) We note that the proposed cable (RG188) is very similar to the cable currently used in TileCal (RG178) and represents only a small increase in the amount of PTFE compared to the existing system. The reason for the change from RG178 to RG188 is to improve the HV compatibility of the HV cable. The new cable provides much better safety margin in terms of HV compatibility than the current cable

Compensatory measures: - HV power supply with overcurrent protection – automatically shuts off in case of short cut - Smoke detector system (sniffer system) - module automatically shuts off in case of smoke detection - Tile Cal modules almost hermetically sealed – low risk of fire and smoke propagation outside module

Are there other previous derogation requests for the equipment/building/installation…?Passive HV dividers currently used in Tile Cal are using RG 178 B/U type cable which have less PTFE than the new cable RG188. However the reason for this exchange to RG188 is the request from the electrical reviewers at the Preliminary Design Review (ATLAS review office) where they required higher safety margin for the maximum HV rating of the cable. Because of this request the RG188 needs to be used which leads to more PTFE than in the current ATLAS TileCal system.We did not find a corresponding derogation request for the presently installed cables.

What are the alternatives that have been investigated and why were they not put into place ? CERN cables and cables from other suppliers do not meet the needs in terms of: - small diameter and flexibility - plastic material that is compatible with the soldering temperature - HV requirements (up to 1000 V) Many cable suppliers have been investigated during the process, only cables of the RG188 from LAPP Cable were found. These cables all rely on Teflon because of the requirements above.

All cables of similar specifications use PE as dielectric and PVC for sheath and they are not suitable for soldering. PVC is also forbidden according to IS 23 and IS 41.

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Documents provided by the requestor: (drawings, reference documents, as applicable)

Active_bases_cable.pdf : illustrates the constraints on the cable. LAPP_PRO294EN.pdf : production specifications of cable. PMT_Block_Position.pdf : shows the insertion of minidrawer into the steel body. MaterialDataSheet.pdf ( drawings, reference documents, as applicable)

Figure 1: Left: ATLAS TileCal PMT block when closed. Middle: PMT block without its metal cover. Right: Active divider and proposed HV cable

Figure 2: Location of the Active divider HV cables: bottom left shows the full calorimeter divided in 256


wedge modules, top left shows a single wedge and the rectangular hole where the electronics is inserted. Middle bottom shows the mini-drawer corss section which is the aluminium frame holding the PMT blocks. The right sketch shows the same object that is shown on the figure 1 left, which is the PMT block with the HV cable.

APPLICABLE SAFETY DOMAIN(a single domain per derogation)

Mechanical (pressure, lifting, machines, HVAC…)

Cryogenics Structural, civil engineering

Fire safety Chemical

Workplace Flammable gas ODH Electrical Noise

Non-ionising radiation Environmental protection Others: define

SPECIALIST OPINION

Specialist opinion

Compensatory measures defined in collaboration with the requestor:

Conditions for the validity of the derogation:

Temporary derogation - expiry date : date _ _/ _ _/_ _ Permanent derogation

Description of the conditions for retaining validity : (duration, requirements,… )

Documents applicable to the reply: (reference documents, as applicable)

DECISION OF HSE-OHS GROUP LEADER

Approved Rejected Requires review by another group : HSE/CEN HSE/FB HSE/RP

Requires approval by the Head of the HSE Unit Comments :


DECISION OF OTHER GROUP LEADERS

HSE/CEN affected

not affected Comments :

HSE/FB affected

not affected

Comments :

HSE/RP affected

not affected

Comments :

DECISION OF HEAD OF HSE UNIT

Approved Rejected N/A

Comments :

TRACEABILITY

Date : EDMS N° : Click here to enter text.

Answered by : Click here to enter text.

Safety actors concerned :
