Equipment – Analog

What is the reason for an explosion proof telephone?

Simply put, explosion proof apparatuses including Telephones, Page/Talk Stations, Talk/Back Stations, Loudspeakers and Ringers are used to protect lives and property in hazardous locations (Class I Division 1 and Class II Division 1 areas).

The design and strength of the enclosure of an explosion proof apparatus controls ingress and egress of a substance’s ability to enter or exit it.

For a fire to start there has to be three elements present – oxygen, heat and fuel. A small spark in a confined room, vessel, building or area where combustible dust particles are present in sufficient quantities and concentration can lead to rapid combustion.

“These five factors (oxygen, heat, fuel, dispersion, and confinement) are known as the “Dust Explosion Pentagon”. If one element of the pentagon is missing, an explosion cannot occur.” – OSHA Fact Sheet, March, 2008

Throughout the world Standard Development Organizations (SDOs) including the National Fire Protection Agency (NFPA) and National Electrical Manufacturers Association (NEMA) work to formulate health and safety standards from electrical codes (NEC) and standards to test methods and product specifications.

Governments in turn have passed laws requiring strict adherence to these codes and standards within their jurisdiction.

Guardian’s EXT-401 Explosion Proof Telephone, CE20 Ringer, SR40/SR60 Speaker/Ringer, EXP & EXP-A Page/Talk Stations, EXP-TBA Talk/Back Stations and OEM Loudspeakers are all designed to operate on standard telephone voltage while containing internal detonations if they occur and keep combustible elements out.

Is a handset the only method of using the EXT-401 Explosion Proof Telephone?

Guardian offers an aviator style headset with a built-in microphone and hand-controlled hook switch.

Are there other methods of telephone signaling to deal with a high noise environment?

Sound, visual or a combination of the two, provide viable methods for signaling within high noise environments.

Guardian designs and manufacturers are own high quality, rugged and reliable loudspeakers and ringers as well as distributing 3rd party strobe lights, loudspeakers and ringers from leading manufacturers. Hazardous area approved models are also available.

SR40/SR60 Explosion Proof Loudspeaker, Ringer & Loudspeaker/Ringer

CE20 Line Powered Ringer

CE20 Line Powered Ringer with horn


What can be done to improve telephone service in a noisy environment?

Dealing with noise is a progression. Noise reduction is standard on all of Guardian’s telephones.

All Guardian Telecom telephones can be equipped with noise cancelling microphones. (The EXT-401 Explosion Proof Telephone is the only exception.)

The next step is volume adjustment. Several methods are available depending on the telephone model.

  • Adjustment by buttons on a membrane key pad
  • Adjustment by volume up and down switch on a handset
  • The EXT-401 has a volume control button option.

If noise levels still make it difficult the final step is an Acoustic Booth. Guardian has a selection of AB-100 or AB-1000 models with up to -25 dB to of sound deadening capabilities depending on the interior liner type.


Why does the EXT-401 Explosion Proof Telephone require an external signal?

The nature of the EXT-401 explosion proof enclosure with its thick, sealed copper free aluminum walls makes it impractical to effectively transmit sound from the inside of the enclosure.

Guardian Telecom offers a variety of options including the CE20 line-powered ringer, configurations of the SR40 Speaker/Tone Ringer and hazardous area strobes.

Is a hand set the only method of using the EXT-401 Explosion Proof Telephone?

Guardian offers an aviator style headset with a built-in microphone and a hand-controlled hook switch.