High visibility jackets

After a recent incident (i wrote about it on here) More things are coming to light.

One thing that I had never thought about and could be a potential hazard are those 'green with white strip' high visibilty jackets.

Here in the UK, they are compulsory things to wear where moving vehicles are, or you need to be seen.

These jackets have a high reflective white strip on them.

This is all in the interests of health and safety at work.

The white strip reflects light.

It is possible to walk in front of a photo cell that uses a reflector for the light beam and have the light beam reflected back to the photo cell via the white strip on the jacket.

This then tells the photo cell that there is nothing blocking it.

It might be common knowledge to some of you but it was a new revelation to me.

There are quite a few possibilities that I have thought of that a man wearing one of these jackets could walk or be and reflect the beam back telling the machine all is clear - when in fact, it is not.


What do we think?

Light curtains do not work with reflections. One pitches and the other catches. The individual beams also form sets, and fire 1 at a time so there is no overlap.

Goody said:

It is possible to walk in front of a photo cell that uses a reflector for the light beam and have the light beam reflected back to the photo cell via the white strip on the jacket.

This then tells the photo cell that there is nothing blocking it.

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If there was something blocking the photocell then it wouldn't see your hi-vis jacket though? Unless you could walk inbetween the photocell and the conveyor, but in my experience, photocells are usually mounted right next to the conveyor and the reflector the other side. You would somehow have to get in between the reflector and the photocell.

And... as mentioned, if there was something blocking the photocell the sensor wouldn't see your jacket anyway. If there wasn't anything blocking the photocell and the sensor did catch a reflection from your jacket then this wouldn't matter either as it would be a true representation of the situation (ie. nothing blocking the sensor)...

I honestly can't see that wearing hi-vis gear represents a hazard with regards to false reflections of sensors...

JT

A retroreflective sensor usually works well unless highly reflective material may pass between the sensor and its reflector. For these situations the 'polarized' type of retroreflective sensors can be used. This type will look for the proper polarized light rotation as provided by the 'corner cube' type reflector. Ordinary shiny or mirrored type material won't provide this rotation.

That being said, of course, a person should not be able to physically fit into a dangerous area controlled by a sensor whether polarized ort not. If thay can then the area must be guarded by the safety light curtain type as described by Mark_H. The shiny reflective material would then not be a dangerous item.

Reflective jacket

It is funny you bring this up, as this same thing has happened to me. It turns out that the reflective band on the jacket was reflecting back to the sensor and starting the process, in this case a conveyor. This type of photo eye only required a return light source to be reflected back. That is, when walking into the pathway of the photo eye you would trigger the process to start up until it was once again blocked by something. Interlocks need to be built in to prevent this function. A timer would work if set up right. Or problem has been resolved and signs have been posted. This id a BIG Safety concern.

Dave

These jackets have a high reflective white strip on them.

Click to expand...

I have used these strips as reflectors for retros before. They work quite well usually. Yes, it is a problem. Use through beam sensors wherever possible. No effect then.

When have retroreflective sensors ever been approved for use in personnel safety????



-Eric

When I posted my post I assumed you meant just using retroreflective sensors under normal circumstances.

As, has already been stated, a light curtain/interlocking gates etc should be used to stop personnel ingress into a potentially dangerous work area. Retroreflective sensors shouldn't be used for this and therefore the hi-vis issue should never arise.

I worked at one plant in the mid ninties where you had to leave your rings and watches in your desk, or tape them up so they couldn't reflect light. Didn't matter if you were even just walking down an aisle. They had major problems.

Several people had aluminum clipboards, and it was discovered they were causing some promlems too. But then, some of it was intentional. Kids nowadays.

regards.....casey

Although I agree that a light curtain should be used whenever personal safety is at stake, I also feel a manual reset should be set up. I know we have some equipment from Europe and whenever a light curtain is used, a manual reset button is needed to clear the "trip". You might want to check to see if this is required by law in your area. I think it is here, but even if it wasn't, I would still do it. An ounce of prevention...

This has caused me some nightmares in our automated warehouse.

When passing alongside the pallet conveyors prior to a palletisation labeller you trigger a pec which tricks the system and puts it out of sequence. You spend ten minutes re-sequencing, placing ghost pallets, etc...

I now wear my hi-viz inside-out. Still bright enough to be seen but gives me less heartache when passing the temperamental sow. Cheap but effective, who needs the shiny-go-faster strips in a well lit area?

One local warehouse had an new outdoor conveyor section with brand new PEs. The sensitivity was set so high that snowflakes were tripping the PEs. A little desensitizing worked wonders.