Fail Safe Sirens

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It's not mandatory in the UK, but regarded as good practice.

You can design the circuit in the following way. Your start command shall activate the siren circuit. The siren will start to work. You can install a sound operated switch ( electronic version ) which shall check the audio sound of the siren and gives a feedback to the control circuit. On getting the feedback the control circuit should activate the conveyor circuit. This arrangement may constitute the " fail safe siren " as required by your application. Do not take a contact from the " siren relay " as a feedback. Try to take the feedback from the sound operated switch.

So the important thing here for the OP is to find out which solution to detect the sound from the siren or it could be a combined device. Sound sensor is intergrated within the siren. I don't know if this would be a good idea or we have a more simple design.

The other is just a normal control practice.

Sirens should be used along side visual warnings. A siren in a crushing or washing plant is useless.

To be honest you should be looking to isolation and safe working practices. People should not be working along conveyors that are liable to start.

It's a very common safety practice to have an audible warning on start-up of moving equipment, but I have never once heard of a 'fail safe" requirement for such. Typically there is just a simple timer that goes off when you hit the Start button, the timer activates the audible warning, then when it times out, the system starts. Generally, the guy hitting the button is the "feedback loop" in this scenario; if he hits the Start and doesn't hear the audible, he hits the Stop.

this question and your other question of conveyors is a good question but as you are a mechanical engineer the practicality of your suggestion and the answer of an audio feed back loop is impossible.

Sirens and flashing lights to warn of conveyors starting is a great idea and used worldwide.. (I know I've worked in a lot of countries) and during REGULAR maintenance these should be tested. The purpose of these are to warn those that are working in the area of the conveyor or near it that it is about to start, as operators/cleaners will be in that area, unlike someone answered, "no one should be working around the area". If that was the case, then why have warning signals?

The chances of BOTH audio and visual warning signals failing at the same time is remote. If its a high noise level area then its a good chance that operators/cleaners will be wearing ear protection so a siren will be almost useless, hence the need for a visual warning sign

However if workers are working on or cleaning on the conveyor, then a Permit to Work should be in force, the primary drive (motor) should be isolated and locked off, and the padlock key given to the supervisor of the workforce. This is where a good safety regime comes into its own, staff are given safety briefs and everyone is aware of whats happening and where.

Your last paragraph brought out some very good points but I would just like to add a point or two, without seeming to be pedantic!

.........should be isolated and tagged and locked out (the person responsible sing and filling out any tags)

..........in my work situations it is the person that is doing the work that holds any lock out keys..........not the supervisor, otherwise things can, and have gone pear shaped very quickly.

good points, however EACH worker (in the western world) should have his or her OWN lock off padlock (with name tag) and not until ALL the padlocks are removed can the prime drive be de-isolated & started.

In third world countries the responsibility is given to the supervisor as thats why he is the supervisor and that what he gets paid for, and I think you'll find our OP is from such a country, again I know, because I've worked there, and many of the workers can't read or write, so completing a PTW & LOTO form will be out of the question as would be personal padlocks.

This, my comment, could be an off topic. But I am feeling that the third countries now, especially, the workers, are trying to work their best to bring the money for the western countries.

In several multi-national companies, because of the globalization, some of workers, in the third parties, who cannot read or write are trying to learn about PTW and SOP... not in their own language... That is what the western countries should think about.

Besides sirens I've seen flashing lights in high noise/hearing protection areas.

We do follow the safety procedure as per SOP. ( Standard Operating Procedure ).

We do follow LOTO ( Lock Out Tag Out).

All our conveyor commands, logics, ( including safety devices ) are routed through PLC.

Giving warning siren prior to starting the conveyor is also SOP. If the conveyor is started without warning siren, the conveyor is started without meeting SOP requirements. The reason could be whatever. Human or Machine or Logic. The reality is SOP requirement was not met.

Regards,

then you have done as much as you can.... why do any more?

Dear all,

Many conveyors are remotely located from the control room and substation where its feeders are installed. They are all remotely operated.

Please assume 650 mm width conveyor. Replacing its carrying roller hardly takes few seconds. Or you may consider removal of an unwanted foreign material from the carrying side. Going as per LOTO may not be always practical.

So we need to depend sometimes on the reliability of pull cord switch and sirens for a very minor jobs. We do follow LOTO, where it is very unsafe and potential hazard to life.

May I compare (Pull cord switch + siren ) to my car pedal brake and LOTO to the (hand brake and wedges for all the four wheels)? Both are necessary and important for the safety of the car, passengers and the pedestrians.

Thanks & regards to all,