The LHC experiments, due to their complexity and size, present many safety challenges. Cryogenic gases are used in large quantities as well as certain flammable mixtures. The electrical power involved calls for analysis of the fire risks. Access is restricted to the minimum and environmental conditions are extremely harsh, due to strong magnetic fields and ionising radiation. This paper will describe the Combined Fire/Gas/Oxygen deficiency Detection systems proposed for inside the ATLAS and CMS Experiments and possibly for the two others, if they deem it necessary. The requirements of the experiments and the development and implementation of such a system will be discussed. In parallel, commercial procedures to implement these systems by industry shall be described, taking into consideration that a previous development has already been undertaken by CERN for the LEP experiments. The stage is set for inter-divisional collaboration in a project of utmost importance for the safety of people and protection of the investment

Nunes, R W

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EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCHORGANISATION EUROPÉENNE POUR LA RECHERCHE NUCLÉAIRECERN - ST DivisionPresented at the 4th ST WorkshopChamonix, France, 30 January - 2 February 2001CERN-ST-2001-02831 January 2001FIRE AND GAS DETECTION IN THE LHC EXPERIMENTSTHE SNIFFER PROJECTR. NunesAbstractThe LHC experiments, due to their complexity and size, present many safety challenges.Cryogenic gases are used in large quantities as well as certain flammable mixtures. Theelectrical power involved calls for analysis of the fire risks. Access is restricted to theminimum and environmental conditions are extremely harsh, due to strong magnetic fieldsand ionising radiation. This paper will describe the Combined Fire/Gas/Oxygen deficiencyDetection systems proposed for inside the ATLAS and CMS Experiments and possibly for thetwo others, if they deem it necessary. The requirements of the experiments and thedevelopment and implementation of such a system will be discussed. In parallel, commercialprocedures to implement these systems by industry shall be described, taking intoconsideration that a previous development has already been undertaken by CERN for the LEPexperiments. The stage is set for inter-divisional collaboration in a project of utmostimportance for the safety of people and protection of the investment.21 INTRODUCTIONFor the LHC Experiments, a great number of alarm systems shall be installed in different locations: onthe surface, in the underground technical and experimental caverns and inside the ExperimentalApparatus. In this paper, only the latter shall be discussed.Both the ATLAS and the CMS Experiment have requested the installation of alarm systemscapable of detecting different hazards developing inside the volume of the Experimental Apparatus.These consist of Fire in an incipient stage, the presence of Flammable Gas or Low Oxygen levelsdangerous for human life.The ST Division has been charged with developing and supplying such systems for theseexperiments, and would like to be ready to receive similar requests coming from the remaining twoexperiments, ALICE and LHCb.2 PROJECT DESCRIPTIONBecause of the lack of space and hostile environment, such a system can almost only consist of anetwork of air sampling perforated tubes accessing the inside of the Experimental Apparatus. Thesetubes would bring a sample of the air present inside the Experiment Volumes to detection equipmentplaced outside.Due to the nature of this project, the name SNIFFER (System to Nail Important Fire andFlammable gas Experimental Risks) is proposed.This project shall be executed by CERN’s industrial partners specialised in this field, with therequirements and supervision by CERN.Figure 1 Principle of Air Sampling DetectionThe technique is known and widely applied in industry and consists of a tube connected to apump with a detection device in the middle. (Figure 1). However CERN is requiring a simultaneousdetection of three different phenomenon: Smoke, Flammable Gas and Oxygen deficiency. This is acomplex combination, taking into account the very different aeraulic characteristics of smoke and gasdetection. The former has very sensitive detectors capable of detecting the most minute particle ofsmoke and works generally with high air flows and large tube diameters (~20mm). The latter has lesssensitive detectors and works with less air flow and smaller tube diameters (~6~8mm)The large dimension of the experiments presents a further difficulty. Being located more than100 m underground and of cylindrical form, ATLAS spans approximately 40m in length and 25m inheight (see Figure 2). This will make for very long lengths of the sampling tubes and consequentlyhigh pressure drops, implying high power pumps. High power pumps in turn take up space, and spaceis a valuable asset in the underground facilities and the size of the equipment must to be reduced to aminimum.DetectorPumpExhaustControlEquipmentAlarmSignal100~150 mDetection Rack(s)Air AirAir3Figure 2 Basic illustration of the foreseen location of the sampling tubes (red lines) in ATLAS3 THE LEP EXPERIENCEFor the detection of fire and flammable gas inside the LEP (Large Electron-Positron) Experiments theEST/LEA group built, more than 10 years ago, the SDN (Sampling Detection and Neutralization)system. This system applied the air sampling principle described above to detect hazards inside theexperiment. It had the additional capability of injecting an extinguishing gas to neutralize any incipientfire.Twenty of these systems were installed in the LEP Experiments, and provide an invaluablereturn of experience to aid in the design of the new systems.It was developed and produced at CERN and is described in detail in [1].4 REQUIREMENTS AND TECHNICAL CONSTRAINTS4.1 Basic RequirementsThe basic requirements from the experiment’s point of view is of extreme simplicity:- The SNIFFER must be able to detect inside the Experiment:- Smoke presence (indication of fire)- Flammable Gas due to a leak- Low Oxygen levels due to a leak of inert Gas.- The response time must be within 100 seconds4.2 QuantitiesBecause of the dimension of the Experiments, they have been divided into volumes inside which thedetection system must work, but they are not isolated from the each other. The volumes are onlyrepresentations of areas inside the detector.For example the ATLAS detector has been divided into slices, each being a volume, and theATLAS Group has estimated the need for approximately 250 tubes. CMS is estimated to requireapproximately 200, and the other two Experiments 50 each.4.3 ConstraintsThe main constraints on the SNIFFER are Distances and Response Time, Space and Location,Radiation, Magnetic field and Access. All these constraints are interconnected.4The response time depends heavily on the length of the sampling tube. The response time is thesum of the air transport time and the analysis time. The longer the tube for a given air speed, thelonger the transport time. So length should be minimized and is expected to be on average of 100m.As mentioned before, space is a valuable asset underground. The choice has to be made betweeninstalling the analysis equipment in the Experimental Cavern or in the Service Cavern.If installed in the Experimental Cavern, distances and response time will be minimized but theenvironment is hostile with Radiation and Magnetic Fields perturbing the functioning of the systemand degrading performances.If installed in the Service Cavern distances will be much longer, and consequently the pressuredrops shall increase, calling for larger pumps that take up more space. The environment is no longerhostile, but the air passing inside the detection system has to be re-injected into the experimentalcavern because of possible radioactive dust. The equipment itself may become slightly active and mayconstitute a radiological problem inside the Service Cavern.Furthermore the Experimental Cavern is under strict Access Control, creating difficulties formaintenance and repair operations. The presence of the whole system in the Service Cavern wouldease the maintenance operations.Due to the large number of detectors needed a solution must be found so as to take up theminimum space. The maximum number of tubes must be analyzed using the minimum number ofracks. This may call for solutions such as multiplexing of tubes or development of very small sensors.4.4 ReliabilityThe SNIFFER must also guarantee reliability and performance, and must undergo a detailed functionalanalysis, and be able to demonstrate that it complies to the SIL2 (Safety Integrity Level 2) as specifiedin the IEC 61508 [2].4.5 Integration into CSAMOf course the SNIFFER must also integrate with CSAM (CERN Safety Alarm Monitoring) system. Itmust be able to transmit its information (e.g. analogue values, alarms, faults, state changes, etc…) viaa communication protocol compatible with the CERN standards, and be able to activate safety actionsand emergency shutdown operations. For more on the CSAM system see [3]5 PROJECT ORGANISATIONThe project should have a structure and its main actors should be organized in such a way as to definethe requirements, provide resources, monitor and control progress and performance.For this purpose, we propose the classic project-management structure (see Figure 3):- Product Owner – Maître d’Ouvrage- Product Manager – Maître d’Ouvrage Délégué- Project Owner – Maître d’Oeuvre- Project Leader – Maître d’Oeuvre DéléguéEach Experiment shall have its own Product Owner and Product Manager. In fact, there shall befour different projects, with four different Product Owners and Product Managers, but with the sameProject Owner and Project Leader.For each Experiment the Product Owner should be the corresponding Experiment coordinator,and the Product Manager should be the corresponding GLIMOS (Group Leader In Matters Of Safety).The Project Owner should then be the hierarchy of the ST Division charged with accomplishingthis project, who delegate the execution to the Project Leader, the ST/AA/AS section leader. He shallcoordinate the internal CERN collaborators, as well as insure a correct follow-up of the project and itsimplementation by the industry.5All Experiments will be slightly different in its constraints and requirements, so it is logical thateach case is treated as a separate project in spite of the common need.Figure 3 Proposed Project Organization6 PROJECT MILESTONESThis project shall be developed by CERN’s industrial suppliers and should respect internal purchasingprocedures. The standard Market Survey followed by Technical Specification must be respected. Inparallel however, some development will be sponsored by CERN, due to the novelty of this project.To make sure that the performances requested by CERN are achievable, prototypes shall bedeveloped to validate the detection principles and assure that the defined detection levels areacceptable.The objective of this prototyping phase is to learn by experimenting, so that an adequate systemcan be designed. A functional analysis must be performed on the detection system, to guarantee that itoffers functionality and reliability. Testing protocols must be defined for the final system.A final Technical Specification shall then be written in order to select the supplier of thesystems to be installedDuring the Experiment assembly, the air sampling tubes must be installed in collaboration withthe experiments and inserted into their assembly schedules. A very close co-ordination shall benecessary during this stage.The main milestones can be enumerated as follows with their indicative dates• Market Survey (10/2000)• Prototyping started (02/2001)• Definition of first constraints (06/2001)• Validation of Prototype (09/2001)• Final Specification and Invitation to Tender (01/2002)• Implementation and Acceptance Tests (2003-2004)• Maintenance (2005)Product OwnerMâitre d'OuvrageExperiment Co-ordinatorProject OwnerMâitre d'OeuvreST Division LeaderST/AA Group LeaderProduct ManagerMâitre d'OuvrageDéléguéGLIMOSProject LeaderMâitre d'Oeuvre DéléguéST/AA/AS SectionLeaderFinal UserPhysicitsDefines the requirementsAccepts the scheduleGo / No GoDefines the teamEstablishes the scheduleMediates conflicts withsubcontractorProvides ressourcesWrites the specificationDefines the final goalCo-ordinationWork Follow-upCollaboratorsEST/LEAST/AA/ASIndustry6Between the start of the prototyping and its Validation the milestone referring to FirstConstraints is of crucial importance. Due to the CMS assembly schedule, the first tubes have to beassembled with the detector in June 2001. At this date, the dimensions of the tubes must bedetermined, so that no further intervention is needed to install tubes in an already assembledexperiment.7 CONCLUSIONThe final goal of this project is to ensure the safety of the personnel entering the experiment, andprevent any major damage to the invaluable equipment in the LHC Experiments.This challenging project, within a complex organization is also technically challenging, pushingour industrial partners to provide ingenious solutions and CERN to new approaches to engineeringprojects. No longer are they performed in-house, but instead rely on the competence of industry. Inthis sense a strong collaboration is required between CERN and its industrial suppliers, who have upto now provided many useful ideas.8 ACKNOWLEDGMENTSA special thanks to J. Nebout, who has been the driver of this project from the start (under a differentproject name). Lots of ideas come from him, who has designed the LEP SDN stations and is preparingto contribute significantly to the development of the SNIFFER.REFERENCES[1] Guy Roux, Michel Jenin, Joseph Nebout, «Genève: Le CERN Expérimente en Sécurité», Faceau Risque Nº 268 Décembre 1990[2] International Standard IEC 61508 – Functional safety of electrical/electronic/programmableelectronic safety related systems[3] S. Grau, P. Ninin, R. Nunes, L. Scibile, C. Soler, 3rd ST Chamonix Workshop Proceedings,CERN-ST-2000-016, « CERN Safety Alarm Monitoring Project »

Fire and Gas Detection in the LHC Experiments: The Sniffer Project

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