14 Safety
Safety is sometimes seen as a boring subject that one pays lip service to if someone else is watching! Health and Safety at Work legislation in the UK has done much to increase safety awareness in industry, maybe not before time, and this book would be failing badly if it did not outline aspects of good safety practice. We shall mention four areas – electrical safety, noise hazards, general ‘mechanical’ safety and fire.
Electrical safety
We are so used to electricity that sometimes familiarity breeds contempt and it is possible for there to be fatal consequences. All mains-powered equipment should be regarded as potentially hazardous, yet the rules for avoiding danger are really very simple.
First of all, the mains plug must be wired correctly – the brown wire to the ‘L’ (live) terminal, the blue to ‘N’ (neutral) and the striped green/yellow to ‘E’ (earth). The latter is vital for safe working. The practice of removing the earth connection to reduce the pick-up of mains hum is a thoroughly bad one.
A most basic rule is never to open up the casing of equipment without first ensuring that it has been disconnected from the supply. And one should never rely on anyone else to do the disconnection without checking. It is all too easy for the other person to mis-hear an instruction to remove the plug from the socket. Besides this obvious rule there are two important safety devices which, properly used and understood, can give essential protection.
Fuses
These protect the equipment and not the person – at least not directly. A correctly rated fuse will prevent an item of equipment from carrying too high a current in the event of a fault causing a short circuit.
To take a domestic item as an example, a typical small hair dryer is rated at about 500 W. This means that it nominally takes about 2 A. The majority of mains fuses for fitting into plugs are rated at 1, 3 and 13 A, meaning that the thin piece of wire inside them will melt and break the circuit if the rated current is exceeded. The hair dryer will clearly need a 3 A fuse. Suppose now that the device develops a fault. As soon as the current exceeds 3 A the fuse will ‘blow’ and no current will flow. If this did not happen, the excessive current could cause the dryer and its cable to overheat with a serious risk of fire, or at the very least, considerable damage to property. It is therefore most important that all electrical items are correctly fused. (Mains plugs are frequently supplied with a 13 A fuse fitted. This is not really a very good idea. It might be better not to provide a fuse but supply instead a little card stating the correct fuse ratings for a range of household objects. It would surely cost no more – possibly less!)
Fuse ratings
Power (watts), current and voltage are related by
Power = Current × Voltage
Assuming that the supply voltage is 230 V – normal in the UK (220 V is more common in Europe) – then the current taken by a piece of equipment is
power in watts/230
It is good enough in practice, and it makes the arithmetic much easier, to take the supply voltage as 250 V. Hence a 500 W item takes about 2 A, and so on. The power rating of most audio equipment is low – below 200 W – and therefore it might seem that a 1 A fuse would be correct. Unfortunately, many pieces of apparatus have an initial surge current, when first switched on, which means that, in this case, a 3 A fuse would be needed.
Increasingly, and rightly, manufacturers state in their literature what fuse to use. The important thing is not to go to the fuse rating higher than the recommended one.
Note, though, that a fuse does not directly protect the person. If one were silly enough to touch the bare wire of a mains cable, the likelihood is that death would occur long before any fuses blew, the simple reason being that currents far less than even 1 A can be lethal.
There are two main aspects of an electric current which can be dangerous. One is the actual current (in amps) and the other is the time for which that current flows in the body. Of course, much depends on the route through the body. A current flowing near the heart, for instance, is likely to be more dangerous than one through the hand only.
Circuit breakers
These fall into two categories: Residual Current Devices (RCDs) and Earth Leakage Current Devices (ELCDs).
The most dangerous fault which can develop in equipment is that in which exposed metal becomes ‘live’. If the fusing is correct, this should result in an immediate blowing of the fuse. However, this is by no means certain. Touching the live exposed metal can be especially dangerous if one is also in contact with another, properly earthed item.
I was once involved as an expert witness in a tragic instance when an electric guitar had become live through faulty plug wiring and the musician holding it had touched an earthed microphone stand.
Out of doors the ground itself will be, very literally, at earth, and the consequences of touching live metal may easily be lethal. Almost certain protection is provided by devices of the ‘Power Breaker’ type. These are plugged into a mains socket and the cable to the equipment is in turn plugged into the device. Units of this sort detect any kind of leakage of current to earth and they interrupt the supply if the current exceeds (usually) 30 mA – about 1/30 A. Furthermore, the British Standard requires the device to operate within one thirtieth of a second. This is considered to give adequate protection against shock resulting from a live/earth current. It does not guard against a live/neutral flow – in other words, getting hold of both the ‘live’ wires. Nothing will protect against that!
The use of RCDs, or their equivalents, should be seen as absolutely essential whenever mains equipment is used out of doors, for example with PA equipment at a sporting event. Their cost is not great and when not being used for audio purposes they can find a place in the home, giving protection when using hedge-trimmers and electric lawn mowers!
Isolating transformers
It can be argued that these give the best protection as they totally isolate the apparatus from the mains. They are, however, bulky and expensive, and only one piece of equipment must be connected to each transformer. (The transformers used in the construction and building industries for use with heavy duty electric drills and the like are usually not true isolating transformers.)
Checking the equipment
So easily put off till another day, this is very important. With equipment that gets moved around, it's more than important – it's vital. A simple check list includes looking for frayed leads, cracks or other defects in the insulation, cracked plug covers, wires firmly held in their terminals, and so on. Regular inspection should be seen as being at least as important as achieving a good recording!
A warning
Many large buildings, theatres and concert halls, and also industrial premises, have more than one phase of the mains present. Without trying to explain this, we will simply say that this can result in much higher voltages than 230 V between items of equipment or machinery connected to different phases. If in doubt, consult the resident electrician or safety officer.
Electric shock
Perhaps this is being a bit morbid, but what do you do if someone gets an electric shock and is lying on the ground unconscious – possibly dead? We all hope this never happens, and I think it's fair to say that incidents of this sort are pretty rare in recording and broadcast studios – BUT!
There are recommended procedures for giving resuscitation, and this book isn't an appropriate place for dealing with them. However, easily obtained wall charts outlining the methods exist and they should be displayed in all technical areas. It's very important that everyone who works in that area knows what to do if the awful situation occurs.
Noise and hearing
This can be a contentious topic. All we will do here is to summarize current UK legislation. Basically, there is a fairly severe risk of permanent hearing damage if the equivalent sound level, denoted by Leq, exceeds 90 dB(A) for 8 hours in each working day.
Before going further we should try to say what is meant by Leq. It is a kind of average of the sound energy which enters the ear. The full definition is rather more complicated, but a measurement of Leq takes into account not only the sound level, but also its duration. Simple sound level meters are unlikely to be able to measure it; what are called integrating meters are needed and these are often of the more expensive kind. However, assuming that there is some way of determining Leq, the relationship which is generally accepted between it and the duration of exposure if the risks of hearing damage are to be minimized is shown in Table 14.1.
Leq dB(A) |
Duration |
90 |
8 hours |
93 |
4 hours |
96 |
2 hours |
99 |
1 hour |
102 |
30 min |
105 |
15 min |
108 |
8 min |
111 |
4 min |
It will be noticed that the permitted exposure time halves for each 3 dB increase in Leq (a 3 dB increase is equivalent to a doubling of the power).
It may be reassuring to say that in normal circumstances there is little likelihood of hearing damage for the person who is not working close to high power loudspeakers for more than a very few hours a week. As an example, a typical professional monitor loudspeaker may be able to produce around 120 dB(A) at a distance of 1 m in front of it. This, note, is the peak power from it. In an ordinary session, the levels will probably be well below that for much of the time, and there will also be rehearsal breaks, and so on. Also, there may be no need to be as close as 1 m from the loudspeaker. At a distance of 3 m, the level will probably be 8–10 dB lower than at 1 m.
Consequently, the Leq over an 8-hour day could easily be below 90 dB(A).
This is not to encourage complacency! Far from it. One should always be aware of the risks which can arise from high sound levels. At the same time, we are trying to avoid being alarmist. What I find worrying is the number of people who drive around with their car windows closed and the radio or cassette player operating at a level which makes it audible some distance away in a busy street, and those wearing ‘walkmans’ which can be heard several seats away on a tube train!
‘Mechanical’ safety
This is not a very good term, but one that may suffice to cover nonelectrical, non-acoustic aspects. A great deal of what follows is obvious common sense, but quite often the obvious needs to be pointed out before it becomes obvious.
The following list is far from comprehensive, but it may be enough to help the reader to think of other aspects of safety.
1. Scaffolding. This is sometimes used to support sound or lighting control areas in theatrical productions. Properly assembled scaffolding is very safe, but if in any doubt an expert should be consulted. Luckily there are, in any community, likely to be builders with experience and knowledge. All platforms must have safety boards around their bases to prevent feet from accidentally slipping over the edge and also to stop things like screwdrivers rolling down into the audience area. Ladders must be firmly lashed and at not too steep an angle; 75° is about right, equivalent to a slope of 1 in 4.
2. Any equipment suspended over an audience must be well secured. Also, it may be against local licensing laws to have microphones hanging over an audience. It is worth checking.
3. We have already mentioned the importance of keeping cables in positions where no one can trip over them. As a reminder:
(a) Take cables over doorways if possible.
(b) Where cables have to be on the floor, then either cover them with mats or carpets or tape them to the floor so that loops, which could catch shoes, cannot form.
(c) With things like table microphones, the mic cables should be tied firmly round the leg of the table as close to the floor as possible. This prevents the cable rising too high if it is accidentally pulled. It can also avoid strain on the cable entry into the microphone and save the microphone from being pulled off the table.
Heavy weights?
Dealing with heavy things can come under ‘Mechanical safety’.
Question: What do you do if there's a heavy item to be lifted?
(a) Show that you're tough and swing the thing up in the air, especially if there's an admiring audience.
(b) Use some sense.
(b) is correct!
There are two possibilities: either you can lift the thing yourself, or you can't.
If you can, then the important thing is to do so without injuring yourself. And what, in these circumstances, is the most vulnerable part of the human body? It's the back. It's a rather fragile part of the anatomy, but if it's kept straight then it's much less likely to get hurt. If you're in your twenties, and many readers are likely to be, you're probably going to laugh at the thought of straining your back. But a little later in life – and not all that much later – people stop laughing! Almost any doctor can tell of patients hobbling into the surgery in the Spring. They've not exercised their backs much in Winter, but with better weather they're out digging gardens – and straining their backs.
So, how do you avoid hurting your back? It's very important indeed when lifting something at all heavy to keep the back as straight as possible. The British Safety Council says:
1. Stand as close to the object as possible and spread your feet to form a stable base.
2. Bend your knees, keeping your back in a straight line – but don't bend your knees too much.
3. Grasp the object and raise your head as you start to lift.
4. Lift, using your legs, not your back.
But what if you can't follow that procedure – the thing's too heavy or too awkward a shape? Then you get someone to help. It sometimes needs a bit of courage to go and ask a friend or colleague to assist you in lifting something, but it's worth it.
Razor blades
Essential for editing tape, these are becoming less common with the increased use of digital editing, but they're still around. I don't need to list the possible risks arising from accidental cuts. It's very important that used blades are got rid of safely. Strong plastic boxes with a slot for the blades are found in many studios – they can be bought from suppliers of audio equipment, but it wouldn't be difficult to make a safe receptacle.
Fire
Everyone ought to know what to do if fire breaks out. Sound studios are usually fairly safe areas, provided there aren't idiots putting lighted cigarette ends into waste paper bins. Nevertheless, ALWAYS BE PREPARED FOR THE WORST.
There are a few basic – and really very obvious – rules:
1. Know where the fire exits are, and make sure they're not obstructed.
2. Know how to call the fire brigade.
3. Be able to identify the correct fire extinguisher.
Knowing what extinguisher to use on what fire is obviously vital. In any studio area, if there's a fire it's likely to be an electrical one – and you DON'T use water to put that kind of fire out! Water is, of course, a conductor of electricity, so putting water on an electrical fire will make things worse. Carbon Dioxide (CO2) extinguishers (colour code BLACK) are generally satisfactory for electrical fires. It's best, though, to have a chart on a wall, showing what extinguisher to use when. Such charts aren't difficult to get hold of.
Fire doors
These are filled with special material that makes them ‘fire-retardant’. That means that it takes quite a while, say half an hour, for heat from a fire to penetrate through the door. Obviously, then, these doors in corridors can help to confine a fire and give people a better chance of leaving the building safely. But fire doors must be kept closed! Don't wedge them open with fire extinguishers, which is a very bad common practice!
And finally
With any event where the public is present, it is advisable to check on insurance coverage. Don't assume that any accidents occurring as a result of your activities, whether you are to blame or not, are automatically covered.
There is an almost endless list of Safety Do's and Don'ts. However, the single most important factor is the right attitude of mind! If you always think Safety you're almost always going to be working safely.
SAFE THINKING = SAFE WORKING!
Questions
1. A small sound mixer is rated at 750 W electrical consumption. What fuse would be appropriate in the mains plug?
| a. 1 A | b. 3 A | c. 13 A |
2. A ladder used to get on to a scaffolding should be fixed at an angle of about
| a. 40° | b. 60° | c. 75° | d. 85° |
3. A mains plug has accidentally got wet. What action would be most sensible?
a. Open it up and wipe it dry as far as possible before using it.
b. Open it up and wipe it dry as far as possible. Then put it in a warm place for a few hours.
c. Open it up and wipe it dry as far as possible. Then put it in a warm place for a few hours. Finally, inspect it carefully for signs of moisture.
d. Reject it.
4. What is the colour code for carbon dioxide fire extinguishers?
| a. Red | b. Black | c. Blue | d. Green |