Intrin­sic safe­ty (sym­bol: Ex i) is wide­ly regard­ed as the safest and most ver­sa­tile method for using elec­tri­cal equip­ment in haz­ardous areas. In this arti­cle, we explain the fun­da­men­tal prin­ci­ples, pro­tec­tion lev­els, and key advan­tages of this explo­sion pro­tec­tion con­cept.

What is Intrinsic Safety?

Intrin­sic safe­ty is a type of explo­sion pro­tec­tion in which elec­tri­cal equip­ment is designed so that nei­ther dur­ing nor­mal oper­a­tion nor in the event of a fault can suf­fi­cient ener­gy be released to ignite an explo­sive atmos­phere. The core prin­ci­ple: lim­it ener­gy rather than con­tain an explo­sion.

Unlike oth­er pro­tec­tion con­cepts (e.g., flame­proof enclo­sure), intrin­sic safe­ty does not attempt to con­tain an explo­sion. Instead, it ensures that igni­tion can­not occur in the first place.

Protection Levels: ia, ib, and ic

Intrin­sic safe­ty is divid­ed into three pro­tec­tion lev­els:

Lev­el	Safe­ty Lev­el	Zone	Fault Tol­er­ance
Ex ia	Very High	Zone 0/1/2	Safe with 2 faults
Ex ib	High	Zone 1/2	Safe with 1 fault
Ex ic	Enhanced	Zone 2	Safe in nor­mal oper­a­tion

Ex ia is the high­est pro­tec­tion lev­el and is the only con­cept approved for use in Zone 0 — where explo­sive atmos­pheres are present con­tin­u­ous­ly or for long peri­ods.

How Does Intrinsic Safety Work Technically?

The core of intrin­si­cal­ly safe sys­tems are pro­tec­tive cir­cuits that keep cur­rent and volt­age with­in safe lim­its:

• Zen­er Bar­ri­ers: Sim­ple pas­sive cir­cuits using Zen­er diodes to lim­it volt­age and cur­rent. Cost-effec­­tive and reli­able, but require care­ful ground­ing.
• Gal­van­ic Iso­la­tors (Iso­lat­ing Bar­ri­ers): Pro­vide gal­van­ic iso­la­tion between the safe and haz­ardous areas. More flex­i­ble since no ground­ing is required on the field side.
• Inte­grat­ed Intrin­si­cal­ly Safe Devices: Com­pact devices such as trans­mit­ters or field instru­ments that are them­selves cer­ti­fied as intrin­si­cal­ly safe appa­ra­tus.

The Intrinsically Safe System: Proving Overall Safety

Intrin­sic safe­ty is not a prop­er­ty of a sin­gle device — it is a prop­er­ty of an entire sys­tem. The proof that the com­plete sys­tem is intrin­si­cal­ly safe is estab­lished through the intrin­sic safe­ty assess­ment:

• Max­i­mum val­ues for volt­age (Uo) and cur­rent (Io) of the asso­ci­at­ed appa­ra­tus
• Max­i­mum val­ues for capac­i­tance (Co) and induc­tance (Lo) per­mis­si­ble in the haz­ardous area
• These para­me­ters must not exceed the enti­ty para­me­ters of the field device (Ci, Li, Ui, Ii)

Only when these con­di­tions are met can the sys­tem be con­sid­ered intrin­si­cal­ly safe and cer­ti­fied accord­ing­ly.

Advantages of Intrinsic Safety

• ✅ Live main­te­nance per­mit­ted: Mea­sure­ments, cal­i­bra­tion, and wiring work may be car­ried out dur­ing nor­mal oper­a­tion (Ex ia/ib)
• ✅ Light­weight equip­ment and cables: No spe­cial armored cables or heavy enclo­sures required
• ✅ Cost-effec­­tive instal­la­tion: Stan­dard instal­la­tion mate­ri­als can often be used
• ✅ High sys­tem safe­ty: No risk of igni­tion from the elec­tri­cal sys­tem itself
• ✅ Zone 0 capa­ble: The only pro­tec­tion con­cept applic­a­ble to appa­ra­tus used in Zone 0 (with Ex ia)

Typical Applications

Intrin­si­cal­ly safe sys­tems are found wher­ev­er instru­men­ta­tion and con­trol tech­nol­o­gy is used in haz­ardous areas:

• Pres­sure trans­mit­ters in pipelines
• Tem­per­a­ture sen­sors (ther­mo­cou­ples, PT100)
• Lev­el mea­sure­ment in tanks and ves­sels
• Gas detec­tion sys­tems
• Posi­tion switch­es and prox­im­i­ty sen­sors
• HART com­mu­ni­ca­tion and field­bus sys­tems

Relevant Standards and Certification

The key stan­dards for intrin­si­cal­ly safe equip­ment and sys­tems are:

• IEC 60079–11: Explo­sive atmos­pheres – Equip­ment pro­tec­tion by intrin­sic safe­ty “i”
• IEC 60079–14: Design, selec­tion and erec­tion of elec­tri­cal instal­la­tions
• IEC 60079–17: Inspec­tion and main­te­nance of elec­tri­cal instal­la­tions
• EN IEC 60079–25: Intrin­si­cal­ly safe elec­tri­cal sys­tems

Indi­vid­ual devices require a type exam­i­na­tion cer­tifi­cate from a noti­fied body such as PTB, BVS, or TÜV. Com­plete sys­tems require an intrin­sic safe­ty assess­ment, which must be pre­pared by the plan­ner or installer.

Conclusion

Intrin­sic safe­ty is the most wide­ly used explo­sion pro­tec­tion con­cept in the process indus­try for good rea­son. Its strengths — live main­te­nance, light­weight instal­la­tion, and max­i­mum safe­ty in Zone 0 — make it the pre­ferred choice for instru­men­ta­tion and con­trol sys­tems in haz­ardous areas.

Do you have ques­tions about intrin­sic safe­ty or need sup­port in design­ing intrin­si­cal­ly safe sys­tems? Con­tact me — I am hap­py to help.