SIL in railway project

[Charbel]

Dear,

I am working on a railway project, but our input is constraint to tunnel ventilation and substation HVAC.

Client is requiring SIL4 to be applied to the tunnel ventilation control system. Ventilation control system controls the exhaust, supply fans based on the temperature measured in some critical locations inside the tunnel.
I was looking on the net, SIL4 requires also to have redundancy in the sensors (maybe triple sensors), I guess it means to have multiple temperature sensors measuring temperature in the tunnel and all of them connected to the PLC, and also for smoke control, PLC will have to shutdown the supply fans and turn on the exhaust fans.

Does SIL4 really required for this kind of application? I believe SIL3 would be enough for the purpose of smoke control.

where is SIL4 usually used in railway application?

thanks a lot for any feedback,

charbel

 

[JDCROCKETT724]

You need to perform a Risk Assessment to determine what safety performance level you need to be at. A quick google search will give you a good idea of what you need to do. http://discover.rockwellautomation.com/Files/633996635845491532.pdf has a quick explanation of this.

 

[CapinWinky]

Ventilation failure in a tunnel could kill many people, which is where the high SIL level is coming in. https://www.yumpu.com/en/document/view/18985573/sensor-failure-detection-in-road-tunnel-ventilation

 

[Charbel]

dear,

thank you for your reply, but I could not open the above link, I don't know why.

 

[Sherlock4me]

Both links opened ok for me. Each has Tons of info on just what you're looking for too. May be worth another try? Could it be a regional thing? or an issue with your computer's settings??

 

[Charbel]

dear Sherlock4me,

yes I could open both link from outside office.

thank you!

charbel

 

[Charbel]

Ventilation failure in a tunnel could kill many people, which is where the high SIL level is coming in. https://www.yumpu.com/en/document/view/18985573/sensor-failure-detection-in-road-tunnel-ventilation

dear,

I checked the upper link its related to ventilation in tunnel used for cars or similar vehicle, but the requirement that I was checking is for tunnels used in railway where a metro would be passing, and usually the temperature inside the tunnel to be maintained at a certain value, over track exhaust and under platform exhaust and jet fan tunnel supply is controlled based on temperature.

So from experience, does an over temperature could call many people and how harmful it might be. if SIL4 is usually used, then it should be ok.

thank you!

Charbel

 

[Charbel]

dear,

I checked today with the client, it seems that SIL4 is needed, but I am not sure how exactly it can be done.
I understand that I would be looking to SIL4 controller but what about the temperature sensors, do they need to be redundant (like three sensors maybe)?

thanks a lot for any feedback,

Charbel

 

[CapinWinky]

SIL 4 is really hard to meet, especially with analog input, because most communication protocols and analog capable safe devices are only approved up to SIL 3. There are special railway computer systems that are SIL 4. I know France approved the use of B&R's safety stuff, but I don't know if that means they meet SIL 4 or France allowed SIL 3 components and protocols.

On the sensor side you would be looking at redundancy to be able to keep operating if something fails, but also the ability to reliably detect failure. For a temperature sensor, if it was a thermal-couple, you could check for wire break or short circuit easily enough and just do two sensors and compare their values to make sure they aren't too far apart. You're bigger problem will be your outputs (to motors and whatnot) where you will need feedback that the fans (not just the motors) are actually spinning or even that air is flowing. It all must be done in a redundant way that allows you to detect failure of both the ventilation system itself AND the sensors providing feedback confirming operation of the ventilation system.

 

[CapinWinky]

I checked and the DDASCA (Dependable Distributed Architecture for Safety Critical Applications) approved OpenSAFETY communication protocol for SIL 4 applications in 2011; however, the current Wikipedia page for OpenSAFETY says it meets up to SIL 3. DDASCA is a consortium of automation manufacturers and related companies, not a standards group like TUV.

There are also SafeNET from Honeywell and LockTrac 6131 ELEKTRA (especially for rail systems).