Client Training Module“optical and acoustic

alarms”

Training Module Basic standards Visual and audible warning devices are used extensively in two areas of alarm systems:

• Fire and Evacuation Alarm Systems• Safety of machinery

Training Module Basic standards “Safety of machinery” According to the European directive 98/37/EC (machinery directive) you have to install appropriate visual and audible warning devices on machineries to alert people of danger.The following standards are the most significant documents in this area:

• EN 457: Safety of machinery - Auditory danger signals; Generalrequirements, design and testing

• EN 842: Safety of machinery - Visual danger signals; Generalrequirements, design and testing

• EN 981: Safety of machinery - System of auditory and visualdanger and information signals

Training Module Basic standards “Safety of machinery”

• EN 60073: Basic and safety principles for man-machineinterface, marking and identification

• EN 61310-1: Safety of machinery – Indication, marking and actuationPart 1: Requirements for visual, auditory and tactilesignals

• EN 60204-1: Safety of machinery – Electrical equipment of machinesPart 1: General requirements

• IEC 73: Coding of indicating devices and actuators by coloursand supplementary means

Training Module Basic standards “Emergency purposes”

• DIN 33404: Danger signals for workplaces; auditory danger signals;unified emergency signal; technical requirements

• EN 60849: Sound systems for emergency purposes

• EN 54-3: Fire detection and fire alarm systemsPart 3: Fire alarm devices - Sounders

• prEN 54-23: Fire detection and fire alarm systemsPart 23: Fire alarm devices – Visual alarms

Training Module Basic standards “Emergency purposes”

• UL 1638: Visual Signal Appliances – Private-Mode Emergencyand General Utility Signaling

• UL 1971: Signaling Devices for the Hearing Impaired

• ANSI/NFPA 72:National Fire alarm Code

Training Module Audible warning devices, basics

Normally the sound level of a sounder is stated in dB(A), measured in a distance of 1 m. But for the coverage area of a sounder there are no general accepted statements available. This value depends on several unknown factors like:– tone – wind speed and direction– air humidity– fog and rain etc.

Training Module Audible warning devices, basics

The subjective or perceived loudness of a sound is determined by several complex factors:• human ear: most sensitive to sounds between 2 kHz and 5

kHz in the average range of 20 Hz to 20 kHz• the sensitivity to different frequencies is more pronounced at

lower sound levels than at higher. For example: a 50 Hz tone must be 15 dB higher than a1 kHz tone at a level of 70 dB

Training Module Audible warning devices, basics

Training Module Audible warning devices, basics

Differentiate: • sound pressure p is a "sound field value" • sound intensity J is a "sound energy value". J ≈ p2

• the volume (loudness) is determined by the sound pressure p and expressed as sound pressure level Lp in dB (SPL)

 

Training Module Audible warning devices, basics

The range of pressure level is between 10 dB (threshold of hearing) and 130 dB (threshold of pain)An increase of 6 dB represents a doubling of the sound pressureAn increase of about 10 dB is required before the sound subjectively appears to be twice as loud.The smallest change of the pressure level we can hear isabout 3 dB

Training Module Audible warning devices, basics threshold of pain >130 dBAero plain, firecracker 120 dBPneumatic chipper 110 dBTruck 100 dBAutomobile 90 dBTelephone, noisy workplace 80 dBBusiness Office 60 - 70 dBBird (nature), conversation 40 – 50 dBClock, living room 30 dBWood, bedroom 20 dBthreshold of hearing <10 dB

Training Module Audible warning devices, calculation

How do I calculate the effective distance and coverage of a sounder?The rule of thumb:• every time the distance from a sounder is doubled, we

have to subtract 6 dB(A) (without immediate obstacles)

Training Module Audible warning devices, calculation

sound leveldistance

100dB(A)

106dB(A)

110dB(A)

120dB(A)

126dB(A)

1 m 100 106 110 120 126

2 m 94 100 104 114 120

4 m (~50m2) 88 94 98 108 114

8 m (~200m2) 82 88 92 102 108

16 m (~800m2) 76 82 86 96 102

32 m (~3200m2) 70 76 80 90 96

64 m (~13000m2) 64 70 74 84 90

128 m (~51000m2) 64 68 78 84

1024 m 60 66

Training Module Audible warning devices, calculation To achieve 82 dB(A) in an area of 50m x 30 m

86 dB120 dB

82 dB

you need 1 sounder 120 dB(A) or not less than 10 sounder with 100 dB(A).Coverage area: 100 dB(A) sounder @82dB(A) = 200 m2

120 dB(A) sounder @82dB(A) = 20000 m2

Training Module Audible warning devices, calculation To achieve 70 dB(A) in an area of 50m x 30 m

you need only 2 sounder with 100 dB(A)

70 dB

Training Module Audible warning devices, calculation To calculate the effective distance and coverage of a sounder you have to know the min. required sound level for the alert signal. The min. required sound level depends on the respective standard like the following:

Standard Min. alert sound level

Min. distance alert & ambient

Appliance

EN 457 65 dB(A) min. 15 dB(A) Machinery

DIN 33404 75 dB(A) min. 10 dB(A) Evacuation

EN 60849 65 dB(A) 6 – 20 dB(A) Fire safety

Training Module Audible warning devices, installation

• normally the sounder will spread in all directions but in an enclosed space some of the sound will be reflected and an different sound level will be result (changes up to 3 dB)

• in general the bigger the distance between the frequency of the ambient background noise and the alarm signal the easier the recognisability of the signal

Training Module Visual warning devices, basics

Visual signaling devices are used in many applications toalert people of danger

• indicate that a hazard is present• indicate that a predefined condition has been

detected• and not least as a reinforcement to an audible signal

(mostly in cases of danger of live)

Training Module Visual warning devices, basics The color is according to IEC 73 dedicated as following (machine directive):RED - danger, act now!

danger of live or unguarded moving machinery or essential equipment in protected area

YELLOW - warning, proceed with care temperature, pressure etc. is different from normal level

GREEN - safety precaution: go ahead checks complete, machine about to start

BLUE - site specified a certain action is required

CLEAR - no specific meaning

Training Module Visual warning devices, basics The effect of lens colour on the perceived intensity of the light source within an industrial environment is quite significant:

Finally according to the inverse square law, the intensity of a beacon is reduced by 75% as the viewing distance is doubled

Colour

Source

Clear Yellow Amber Red Blue Green

Xenon 100 % 93 % 70 % 23 % 24 % 25 %

Filament 100 % 95 % 70 % 30 % 17 % 12 %

Training Module Visual warning devices, recognisabilityLight travels in straight lines, so the beacon will be far more effective if positioned in the line of sight rather than relying on reflections.Differences between the luminance of warning and alarm signals:

• luminance of warning device has to be 5 times higher than the luminance of the ambient light

• luminance of alarm device has to be 10 times higher than the luminance of the ambient light

If the visual signal is used as a alarm signal it should always supported by a sounder (EN 842)

Training Module Visual warning devices, recognisabilityAnother general rule for the effectiveness and coverage of a Xenon beacon with clear lens, installed in an industrial environment is shown below:

The inner circle defines the alarm distance where an observer’s attention would be attracted if he was not looking in the general direction of the beacon; the outer circle represents the distance where an observer would be unlikely to see the emitted light if he was not looking in the direction of the beacon.

Training Module Visual warning devices, recognisability According to the NFPA 72 the effective intensity of the alarm device, measured in candela, is the base of selection. The following table gives an example:

max. room size (m x m)

min. required light output (effective intensity [cd])

1 light / room 2 lights / room 3 lights / room(synchronised)

6 x 6 15 not allowable not allowable

12 x 12 60 30 15

18 x 18 135 95 30

24 x 24 240 135 60

Training Module Visual warning devices, recognisability

• considering the huge complexity of the optical environment a system of optical alarm units should be examined by a representative selection of persons

• in all applications, the worst case ambient light level must be considered and it is very important to install the beacon in a suitable location

• the worst that can be done is simply installing the cheapest and most ineffective model because standards simply demand „a beacon“