The Law regarding Fire Alarm Systems.

[Wiz]

Hi Wiz,

Why are you talking about earthing?

I've already explained that other readers were simply curious to know why the 17th Edition of BS 7671 fails to comply with the EAWR, that is the only reason that earthing has been discussed.

The problems concerning fire alarm systems have nothing to do with earthing, please take a look at the drawings that Kurnal has referred to above or read through this forum from the beginning before speaking again, otherwise I'm sorry to be rude but you are just wasting your breath.

David, I'm talking about the things that I understand that have been brought up by your original question, and that seems to me, to be about electrically conductive surfaces not being earthed. Since I am interested in fire alarms, and you claim that they are affected by the problem, this is obviously what grabs my attention.

If I have misunderstood your point then I trust you will be able to explain it a bit better without using silly phrases like RCDs 'cook' people and MCBs make them 'crispy'. I can't believe there are many people on this forum who don't know the difference between an MCB and a RCB, and I believe you are only  'talking down' to them if you use such phrases

Your subsequent explanation was far more useful for those who know very little, but the claims of death being caused by as little as 2mA is hyperbole when talking about everyday situations. Also you make no mention of the affect of muscular reaction when affected by alternating currents.

You have also made scaremongering claims that electricians are going to be punished in the future for following standard practice today. You also claim that fire alarm designers & installers will also be dragged into this problem. I say it is very unlikely to happen.

You admit that your past representations to various authorative organisations have been ignored. I wonder why this is? Why isn't the NICEIC or ECA interested in this supposed 'problem'?

If you are only trying to say that there is clash in some combination of different laws and/or recommendations, then I say that this sort of problem is endemic and affects many areas of life and business, and it obviously doesn't matter that much to anyone.

And where is all the data on the thousands/hundreds/dozens of people being killed every year because of this problem?

[Wiz]

David I am sure there are many  here able to answer you but I wondered if you are also aware of another forum

http://firealarmengineers.com/forum/

You may find answers there too.

Thats a sneaky move, Prof! 

[kurnal]

Just trying to be helpful as usual Dr Wiz.

[David Rooney]

I think that particular forum is full and there are a few people who may not be as restrained and polite as the members here, and anyway they're no where near as clever as Kurnal....... 

[kurnal]

I think that particular forum is full and there are a few people who may not be as restrained and polite as the members here,

You must be referring to that stroppy ESP person?
Yes we are fortunate in our members they very rarely get abusive and can be relied on to give people the benefit of the doubt. 

It sometimes isnt easy to express yourself in a chatroom such as this without the other cues such as body language etc and I am often suprised at how some of my postings are not read in the way I intended. Especially when trying to be humorous  or brief. Brief responses are so often seen as flippant, ignorant or arrogant.

[Clevelandfire 3]

It sometimes isnt easy to express yourself in a chatroom such as this without the other cues such as body language etc and I am often suprised at how some of my postings are not read in the way I intended. Especially when trying to be humorous  or brief. Brief responses are so often seen as flippant, ignorant or arrogant.

Yes and to think Wiz has been critical of me in the past for my responses, yet he has been very bolshy toward a new member. A timely reminder that all is not as it seems on an internet forum without having the benefit of tone of voice and body language.

[Wiz]

I believe David is exaggerating the 'problem' he claims and also scaremongering somewhat. However he is entitled to his opinions and I welcome his views. I just hope he that he doesn't believe that I have to agree with everything he says and allows me to question his claims that I don't believe in or understand.
I also tend to be a touch sarcastic when I believe that someone is 'talking down' to me or other members. I apologise unreservedly to David911 if he has been hurt by my sarcasm.

[kurnal]

David I have not shared your documents with anybody, I am happy to forward them to anyone who requests it but have no access to a server on which to place them for general access. Other members who regularly post photos do have such access  and may be able to help.

[kurnal]

If I have designed, installed and maintained in accordance with the accepted best practice guidance BS5839 I will have nothing to fear from the judge.

Is it safe enough? Better minds than mine have decided that it is.

Your argument has some merit no doubt but s it not similar to the following  scenario?
The Highway code says I should drive at a maximum of 30 mph in a built up area. If I hit a child at 30mph I will kill them. If I hit a child at 20mph I probably will not. So the Highway code is a dangerous document. It should say we should all drive at a maximum of 5mph and a man should walk in front with a red flag to warn pedestrians.

[Wiz]

ELECTRIC SHOCKS
The effect of an AC electrical shock on a human being depends very much on the AC cycle frequency and the voltage.

There are also numerous factors that affect the effect of an electric shock, and probably most importantly, the route through the body which it takes

A human being exhibits an electrical resistance between dry fingertip to dry fingertip of up to about 100K Ohm. This means a current of approx. 2.3 mA would flow at a voltage of 230V. This would barely be felt.

Even if the electrical circuit is backed up by an 100A fuse, this doesn't mean that 100A would flow through the human body because the electrical resistance of the body limits the current that can flow.

Obviously sometimes, due to skin moisture etc, the resistance to electrical flow will be far less and then a higher current will flow and the electric shock will be felt much more.

Many 'mains voltage testers' rely on the human body providing part of the electrical circuit to illuminate the neon. A resistor incorporated within the tester circuit restricts the current flow to well below 1mA where it cannot even be felt.

Electricians suffer electric shocks from mains voltages many times throughout their working lives without any ill effects.

Many electricians actually test for the prescence of 230V AC mains voltages by earthing a finger of one hand and then touching the suspected 'live' conductor with the thumb of the same hand. This causes just a bit of a tingle.

Touching a 50 Hz AC electrical potential with a finger generally causes the the arm muscles to involuntarily to contract drawing the finger away from the source.

Generally there are very few fatal electrocutions to humans at current flows of less than 100ma.

If a human exhibited a resistance of only 1000 Ohms (perspiring greatly?) then the current flow at 230V would be 230mA and highly probably fatal.

The Guiness Book of Records that someone survived an electric shock from a 340,000 V source.

However, no-one should ever underestimate the potential dangers of electric shocks.

If the electric shock caused a burn which broke the skin and the outermost layer of the epidermis then the electrical resistance of the body will dramatically reduce. This burning is normally mostly a problem at voltages over approx. 400V.

Ventricular Fibrillation may occur at currents as low as 50mA and if electrodes are placed directly either side of the heart at currents as low as 1 microAmp.

AC is more likely to induce fibrillation than DC voltages.

The higher the AC cycle the more chance that muscles will actually seize than contract.

However, the statistics show that there are surprisingly very few fatal electrocutions of humans from the domestic power supply, without the circumstances of moisture being involved in some way, in respect to how close we all come to it every day.

The introduction of electrical safety devices such as RCDs have greatly contributed to this.

FIRE ALARMS

The Oxford Dictionary definition of the term 'radial' is 'diverging in lines from a common point'. In fire alarms we use this term to describe a method of circuit wiring to differentiate it from loop wiring.

The use of a minimum of two alarm sounder circuits in fire alarms when using radial circuits is to
try to prevent losing all sounders should a fault occur and so that occupants of an evacuated building don't return to an unsafe building thinking that the fire aalrm system had been reset because they've heard the sounders silence. In fact BS5839-1 actually recommends (but doesn't insist) that just one sounder is connected to one of the circuits and positioned adjacent to the main control and indicating equipment (which is likely to be positioned close to the main entrance to a building).

To try and achieve the same level of cover on loop wired systems BS5839-1 recommends that the first or last device on a loop is an alarm sounder mounted adjacent to the cie and then protected either side by a loop short-circuit isolator. I believe an earlier post suggested that other devices might be connected as the first devices, which is incorrect.

[Mike Buckley]

"Now if you will all forgive me I will indulge in some theoretical 'scaremongering' simply because this is the easiest way to get the point across: Audible warning devices are constantly transmitting a message, if they are operating there is a fire, if they are operating intermitantly there is a fire somewhere close by and if they are silent you are safe. Therefore if during a fire a person reaches an area where the audible warning devices are silent that person will assume that they have reached a safe place, therefore if those audible warning devices have failed and the fire is actually close by that person could be hurt as a result!"

In my view this is the wrong interpretation. If the audible alarms are operating you must leave the premises to a place of safety. If they are operating intermitantly this is part of a phased evacuation process and you should prepare to evacuate. Once the evacuation has started you should evacuate the premises and not return until told it is safe to do so.

Once the evacuation has started a person is not safe until they have reached a place of ultimate safety (normally outside the building).

The audible warning devices are tested as part of the weekly fire alarm test and any failures should be noted. Having done that the occupier has done everything that is "reasonably practicable" to ensure the system is operating. No court case.

[deaconj999]

David I am sure there are many  here able to answer you but I wondered if you are also aware of another forum

http://firealarmengineers.com/forum/

You may find answers there too.

Started off well, got interesting, feeling drowsy, dreams of http://www.electriciansforums.co.uk/, ZZZZZzzzzzzzzz........

[kurnal]

David I am sure that Wiz was not trying to mislead anybody he was expressing his point of view. And very few people have a better technical and practical understanding of fire alarms.

I can relate to some of what he says, when I left school and before joining the fire service I worked in a TV repair shop in the old days of valves when most sets had a "Live chassis" - the intention was that the neutral was connected directly to the chassis of the set. That was in the days when many homes were still on round pin plugs which were often reversible. Many of the old timers when servicing in the field used to very quickly and lightly touch the chassis of a set before working on it to check if it was "live ".


To be honest I feel this discussion on earthing is going outside the remit of the firenet forum and may be better exercised on other forums.

As far as people getting killed or injured by fire alarm sounders failing, there is no evidence of this occuring. All fire brigades fill in a FDR1 form to report on all fires and one thing they are required to specifically report is the failure of fire safety systems. If you wish to persue this you could ask the DCLG for their data.

But I  served 31 years in a fire brigade and never encounrtered this as a problem, yes alarms were eventually damaged by serious fires but the people had long since left. After all the goal in most buildings is the early detection of fire by smoke detectors and the efficient evacuation of a building when the alarm sounds, in most buildings to be complete  within 2.5 minutes of the alarm sounding.

[kurnal]

Is this incident documented in the public domain? How was the signal to evacuate passed around?

I would be interested to know the detail of what happened.

[Mike Buckley]

"A couple of years ago one of the Hospitals in London evacuated 800 staff and 80 patients in complete silence during a fire!"

It is wrong to associate raising the alarm with bells and sirens going off all over the place. There are places where it is impractical or even dangerous to use the "usual" type of sounder. The classic example always used to be cinemas and theatres where a certain tune played over a tannoy system would alert the staff to start evacuating the audience. Also in  hospitals there is a question of whether alarm bells going off would cause more problems by uspetting and panicing the patients or whether another system should be used.

The highlight of your comment should be that 800 staff and 80 patients were safety evacuated during the fire, not that they weren't deafened by the bells whilst they were doing it!

The main thrust is to look at the goal, which is to get everybody out in case of a fire, and then follow it up with the method, which is normally, but not necesarily, a BS5839 Fire Alarm System.

Thank you for your offer to look at the diagrams but I am not an electrician or a fire alarm installer and they would probably mean nothing at all to me.