Stair lift safety

[ericmark]

My parents had a stair lift fitted by local council 6 years ago and I never gave it a second thought. However it went wrong out of guarantee so I got involved in finding out what was wrong and getting some one to repair it.

It seems it runs from 4 batteries which of course makes sense one does not want it to fail in a power cut. One battery in the chair (24v) one in the extension leg which drops across the hallway (size unknow) and one in each of the remote controls (9v) the track twists back on it's self where the stairs on a landing turn a full 360 degrees so from the top of the stairs one can't see the bottom. The chair has three charging points one at bottom which can't be used as it's on the retractable arm. One on first bend the normal parking point and one at the top. The chair will not move until the extension leg has been dropped. It would seem the two static controls are radio linked to chair and extension and use a replaceable 9v PP3 cell.

I have two concerns:-
1) The extension legs seems to have no sensors or beams even load sensing and my attempts to stop it moving did not even make the motor grown. The upper control station is positioned so the leg is completely invisible and the operator relies on the noise alone of it working to know when it has fully extended. So any animal including children lying or playing under the arm could be trapped and crushed by the descending arm or any items placed on the floor could be crushed. My dad's hearing is not what it use to be so he tends to count then try lift rather than hear the leg grown so would be likely to miss sounds of items being crushed.

2) Since radio controls are used could some other item like a 400W UHF radio used by my visiting friends trigger the arm or lift?

I have memory's of watching Gremlins and although I realise the speed could not increase and send the user off the end like in the film could it start up on it's own? And nearly as bad could some one chatting to me while waiting for me to arrive on one of the amateur bands or even members of the emergency services using their two way radios, stop it working and maroon my dad?

From the Stennah web site seems the chair does have safety edges but since my dad is sitting on the chair to work it and he has to hold the leaver over to work it, it would be very unlikely he would run into anyone or thing with the chair. It's the extension leg which is the problem.

My mother is in a wheel chair and unless the extension leg is lifted she can't pass it to either reach the controls or to get to the front door which is only door with a ramp so her only means of getting in and out of the house.

As an industrial electrical guy I am sure I would have been in very hot water with HSE if I had designed and commissioned some thing like this and that's where there are no children, pets, or old age pensioners working or playing near the equipment.

 

[bhm1712]

i cant really picture what this extension leg is for or what its doing..but:

I wouldnt have thought an average person would be able to even get close to stalling the motor - i would have thought the chair is rated upto a certain weight and it will power through any force applied upto that weight..just think that sometimes an overweight person could be using it and the performance would need to be the same for a 50kg person, as a 100kg person etc etc.

Do you mean that the chair doesnt automatically stop/turn off at the top or bottom and the user has to stop it on the buttons?

H&S in the home is a complete different kettle of fish than what we industry guys are used to...im in the same boat - manufacturing.

I also wouldnt imagine that radios or anything else would affect the operation, as the frequencies will be completely different. Just the same as your car remote wont operate another cars locks, and your cordless phones wont set off the doorbell.

 

[mattylad]

The radio signals are more likely to cause EMC issues than affect the RC side of it, still just as bad as then things would be entirely unexpected.

Given the suggested lack of safety cutouts then DFE is likely to be poorly thought out too.

I have seen extension legs before, fold over at the bottom of the stair perhaps? (I fell over one several times).

 

[ericmark]

I also wouldnt imagine that radios or anything else would affect the operation, as the frequencies will be completely different. Just the same as your car remote wont operate another cars locks, and your cordless phones wont set off the doorbell.

Using my 2 meter and 70cm radios has in the past locked car doors and set off door bells. I am licensed and 400W is very different to the milliwatt used with other items which share the use of the 70cm band. OK I only use 5W but I could easy have a friend visiting who could easy use 45W and is licensed to use 400W. Power like this can and does swamp many systems designed to stop interference.

The leg motor does not move anyone. All it does is place a lenght of track at the end of the run before the lift is used and remove it again after because there is not enough room to get around the end of the track without having the last bit lift out of the way when not in use.

However the way the rams work mean the load on the motor is not constant so the motor is much bigger than really required to do the work as there are no ballast weights, springs, or other compensating gear that I can see. So the motor is quite powerful. I had expected to find there was a clutch of some type to limit the power the arm could exert but trying to stop it did not seem to activate any safety system.

 

[ban-all-sheds]

As an industrial electrical guy I am sure I would have been in very hot water with HSE if I had designed and commissioned some thing like this and that's where there are no children, pets, or old age pensioners working or playing near the equipment.

Yup.

And try comparing the height of kitchen worktops to the height required for workstations where the user stands....

 

[bernardgreen]

My mother had a similar stair lift.

bhm1712 asked

i cant really picture what this extension leg is for or what its doing.

It extends the track at the end of the track into an area where the user can get in or out of the chair and then removes it to allow peopl to use the area. In my mother's case the area was by the doorway into the kitchen so the track could not be there permanently.

On my mother's there were position sensors on the leg and a timer such that if the leg didn't reach commanded position within a certain time then the power to the leg motor was cut off and the chair locked. Her lift was not battery backed and power and control to and from the chair was via a cable that wound and un-wound from a spring loaded drum on the chair.

Mum could walk up and down in emergency so that may have been why there was no battery back up.

I fitted an automatic emergency lamp on the stairs in case of a power cut as stair obstructed by a chair lift are hazardous in the dark.

 

[TicklyT]

Some things have improved.

The old one my stepson used had a folding track section. the only 'safety devices' for the folding track section were limit switches for up and down. The 'down' limit cut all power to the chair until it operated. It was all 240 Volt powered, with 24 Volt coltrols. All the controls for track and chair were hard wired via a myriad of alarm cables running up and down the stair stringer like tram lines.

The track raising motor worked through a worm drive gearbox plus an additional spur gear reduction to a gear quadrant to swing the track up and down, again without any counterbalancing or springs, so the motor had to deliver plenty of torque, and the worm drive meant it couldn't be forced backwards.

There was a time delay of about 3 seconds - all done with relays - between pushing the start button and the chair moving. Let go of the button, and everything stopped dead. No soft start for the motor either - It was all or nothing!

The emergency backup for the chair movement was a screwdriver slot cut in the end of the motor shaft and a small 'starting handle' to plug into it through a hole in the case (an electric screwdriver plugged into the slot shifted it quite easily). The cable to the chair itself was a heavy ribbon cable anchored at the top of the rail, run around a bobweight inside a box section in the track, back up over a roller and down to the chair. That was fine for a straight track, but I can't see that system working very well around corners.

 

[SimonH2]

Just for good measure, the house I bought last year had a stair lift in it. When I pulled it out, the supply was tapped out of the back of a socket in the living room, through an RCD, and an FCU. Apparently, in the minds of the installer, the presence of an RCD obviates the requirements for any earth at all for the metalwork since he didn't bother connecting an earth from the back of the socket to the FCU

 

[Alarm]

You could use some "safety" features from auto gates. Such as "Safety Edges" or beams.

http://www.theelectricgateshop.co.uk/Category-131/gate-safety-edges

 

[ericmark]

As far as I can make out the whole lift is powered by 4 batteries 2 primary and 2 secondary it uses two 9v PP3's and 3 x 12v lead acid one single battery 12 volt for leg and one double 24 volt for chair all being charged from a single double insulated charger

Untitled

• ericmark
• 5 Feb 2012
• 2

so I can understand why there is no earth bonding.

However I would consider any metal work which could transmit a fault in one area to another should be earthed as we do with gas and water pipes. But with my parents lift I think the risk is very low and I can understand why there is no earth.

It is the mechanical side which is a worry the control to drop leg seen here

Untitled

• ericmark
• 5 Feb 2012
• 1

at the top of the stairs has a PP3 battery to power it. But one only has this

Untitled

• ericmark
• 5 Feb 2012
• 2

view down the stairs so one can't see this leg

Untitled

• ericmark
• 5 Feb 2012
• 2

The controls are repeated at the bottom, but these

Untitled

• ericmark
• 5 Feb 2012
• 1

are the wrong side of the leg to be accessed by my mother once it is extended. The chair details are

Untitled

• ericmark
• 5 Feb 2012
• 2

and there is a manual method

Untitled

• ericmark
• 5 Feb 2012
• 2

but in real terms this is only of use to a service engineer. So my problem is:-

Once leg is extended it stops anyone in a wheel chair accessing the lower controls so if left down my mother can't lift them.

From the top my father can't see if the arm is up or down and he has to go by sound alone.

One can't use the chair until the arm is lowered so one can't go half way down the stairs to check all is OK.

Although by trying to use the chair one can work out if fully extended one has no way to know if fully retracted.

The controls for leg are radio controlled so one wonders if it could start without pushing the buttons.

The simple answer would be a second set of buttons down stairs so my mother could lift the leg if my father had failed to do it. However even that still means my father has to drop the leg blind and anything under the leg would be crushed.

What seems strange there are loads of safeties on the chair but non on the leg.

My mother has problems with her wheel chair where the front caster wheels lock and stop her from moving. She can in the end free it but it takes some time. Should this happen under the arm then she would likely be seriously injured. With this in mind my father often walks down the stairs or at least sits on them and goes up and down one stair at a time rather than put my mother or dog at risk.

Clearly this is not what is wanted.

 

[Alarm]

One option is to move the staircase Bannister side where the buttons are now and use a "curved leg" so no drop arm.

Why not ask Stannah if they have other options.
It must have been alright at install?

 

[ericmark]

Not really an option. I am sure there should be sensors to tell one when it is raised and to stop it if it is fouled by anything. If it had used a hard wired system this would have been easy. But it's all radio controlled. To work the chair with a radio control yes but not a clue why the leg is radio controlled.

Clearly there must be a radio signal from the leg to the chair so that the chair will not move until the leg is lowered. If this was not done then it would be easy to move half way down before lowering the leg so one could see what is going on.

Just poor design. I would expect the leg is designed for use with a straight track so one can see the leg when being lowered but who ever installed it has not though about it and has combined a 180 deg bend and a leg together which I would not think was really intended to be done.

It seems the lift now belongs to my parents as over 5 years old so any alteration has to be paid for by them. I would have thought the council would have checked the lift but clearly they did not. I had seen it was fitted but did not think about safety I assumed it would be safe. It was only when it stopped working that I started to look at it and realised the problem.

My cure would be second remote control and a convex mirror on the stairs.

 

[Alarm]

Ask the makers, perhaps there were design constrictions. Maybe there is another solution now.

 

[TicklyT]

How about a PIR detector covering the space at the bottom of the stairs set up to override the upstairs switch if someone is in the hallway?

 

[Alarm]

How about a PIR detector covering the space at the bottom of the stairs set up to override the upstairs switch if someone is in the hallway?

Well thats what I was suggesting with "Gate and barrier" accessories. As they are all durable and on the same voltages.