ALERTS THAT ARE SURE TO BE HEARD

Audible signals provide information, a warning or alert, for example in the event of equipment malfunctions or safety issues, or when plants are starting up. To design audible signals that are perfectly suited to the ambient conditions, some terms, i.e. volume, sound pressure and sound pressure level, need to be clarified first.

WHAT APPROACH SHOULD BE TAKEN FOR PRACTICAL USE?

The motto of "the more, the better" does not apply to audible signals. For practical applications, it is firstly important to clarify why audible signals are used. When using local signals to provide notifications and warnings, excessively loud signals should be avoided in areas containing many signalling devices. This is because, on the one hand, they generally increase the noise level (two identical sound pressure levels increase the total sound pressure level by 3 dB) and, on the other hand, they may affect the physical and mental well-being of employees. Too many signals, or disproportionate signals, are overwhelming and harmful to health, lead to sensory overload and result in incorrect responses. This is why hearing protection is recommended at a sound pressure level of 80 dB and above, with this being a mandatory requirement from 85 dB.

AMBIENT VOLUME NEEDS TO BE CONSIDERED

In contrast to this, when emitting long-range warning or alarm signals the signalling device must be significantly louder than ambient sounds (at least 15 dB is the recommended value) in order to clearly convey all of the necessary information. Alongside the signalling device's sound pressure level, other factors to be taken into account include loss due to distance (accounting to 6 dB each time the distance is doubled) from the signalling location and the prevailing ambient conditions, such as wind, humidity, machinery and noise from people. For a clearer idea of this, the sound pressure level in production areas is usually between 60 and 80 dB.

In practice, due to the aforementioned audible condition, R. STAHL signalling devices with sound pressure levels from 70 to 120 dB (including volume reduction) are ideal for being heard without causing any harmful effects or annoyance. These are suitable for conventional areas of application owing to the increased sound pressure level in the vicinity of machines (e.g. milling and punching), among other factors.