- For everyday work in Zone 1, an intrinsically safe phone is the more robust and more practical choice than a smartphone in a flameproof enclosure.
- An intrinsically safe phone is safe because of how its circuits and battery are designed. A flameproof phone is safe only while its enclosure stays intact.
- Flameproof smartphone enclosures are commonly certified with a low impact limit on the glass, around 2 joules. A phone slipping from a pocket or a hand carries two to five times that energy.
- A damaged flameproof enclosure cannot be repaired on site, and the enclosure adds weight, muffles audio and closes off the ports.
A buyer who needs a smartphone for Zone 1 now meets two kinds of certified device. One is a purpose-built intrinsically safe phone, marked Ex ib. The other is an ordinary consumer smartphone sealed inside a flameproof enclosure, marked Ex db. Both are certified for Zone 1, and both are legal to use there when they are used as their certificates require.
They do not behave the same way in a worker's hand, though. One keeps its protection however it is handled. The other depends entirely on a shell of aluminium and glass staying perfect through every shift. This guide explains the difference, and why intrinsic safety is the better choice for most Zone 1 users.
Two ways to make a phone safe in Zone 1
Intrinsic safety, Ex i (IEC 60079-11), prevents ignition. Battery current is limited, protective components are duplicated and encapsulated, and every circuit is designed so that its sparks and hot surfaces stay below the energy needed to ignite the gas. For level ib this must hold even with a fault. Gas can reach the electronics, because the electronics cannot ignite it.
Flameproof enclosure, Ex d (IEC 60079-1), contains ignition. It accepts that gas may get inside and that the electronics may ignite it. The enclosure is built to withstand that internal explosion, and every joint is a flame path: a narrow, precisely controlled gap that cools escaping gas before it reaches the atmosphere outside.
Inside a flameproof phone
Published IECEx certificates for flameproof smartphone assemblies describe a broadly similar design. A current consumer smartphone sits inside an aluminium enclosure, behind a toughened glass window for the touchscreen and further windows for the camera and wireless charging. The buttons pass through the enclosure, and the gap around each one is itself a flame path. Lids and windows are cemented in place or closed with fasteners of a specified strength, and rubber bumpers protect the corners.
These assemblies are certified to IEC 60079-0, IEC 60079-1 and, for dust, IEC 60079-31. Because the method is containment, the assessment centres on the enclosure. The smartphone inside is treated as a possible ignition source, and its circuits are not assessed for intrinsic safety. Everything therefore rests on the enclosure.
Why intrinsically safe is the better choice for Zone 1
1. Protection that does not depend on the housing
An intrinsically safe phone carries its protection in its circuit board and battery pack. Scratches, scuffs and a cracked screen do not, by themselves, open a path for ignition, because the energy limits are designed into the circuits. A damaged device should still be checked as its manual requires, but its basic protection does not wear away with the case.
A flameproof phone has a single layer of protection, and it is the outer shell that takes every knock. A hairline crack in the window, a dent at a joint or a closure that is not fully refitted can open a path for flame. Nothing inside the enclosure makes up for that.
2. A normal drop can exceed what the window is certified for
IEC 60079-0 includes impact tests for enclosures and for light-transmitting parts such as glass windows. Equipment can be certified at a reduced impact energy when the risk of mechanical damage is considered low. The certificate number then ends in X, and the specific conditions of use state the limit. Published certificates for flameproof smartphone enclosures commonly state a low impact limit for the glass, around 2 joules, or simply require the device to be protected from high impact.
Two joules is the energy of a 1 kg weight falling 20 cm. Phones do not fall that gently. The energy of a dropped object is its mass multiplied by gravity and the drop height. For flameproof smartphone assemblies, which weigh roughly 400 g to 750 g, everyday slips look like this:
| What happens | Height | 400 g phone | 700 g phone |
|---|---|---|---|
| Slides off a desk, bench or vehicle seat | 0.75 m | 2.9 J (1.5× the 2 J limit) | 5.2 J (2.6×) |
| Slips out of a shirt or trouser pocket while bending | 1.0 m | 3.9 J (2×) | 6.9 J (3.4×) |
| Slips from the hand during a call or while taking a photo | 1.5 m | 5.9 J (2.9×) | 10.3 J (5.2×) |
| Falls from a ladder, stairway or platform | 3.0 m | 11.8 J (5.9×) | 20.6 J (10.3×) |
Bumpers and the angle of the fall absorb part of that energy, and not every drop breaks the glass. But every one of these ordinary slips goes beyond the impact the window was certified for. Purpose-built intrinsically safe phones, by contrast, are typically designed from the start as rugged handsets, with their drop resistance stated on the datasheet.
In practice, every drop of a flameproof phone has to be treated as a possible loss of protection. The glass, joints and corners must be inspected before the device goes back into the zone, and any crack, chip or dent takes it out of service.
3. Damage means downtime
Flame path dimensions are controlled to fractions of a millimetre, and the certificates for these devices prohibit repair of the flameproof joints. A damaged enclosure cannot be fixed by a site technician or a phone shop. It goes back to the manufacturer or an authorised facility, and the user is without a phone until it returns, unless the site holds a pool of spares. An intrinsically safe phone also needs certified repair under IEC 60079-19, but minor wear to its housing does not, in itself, end its protection.
4. Closures that rely on the user
To charge the phone inside or change the SIM card, some flameproof designs have a cover or plug that the user removes in a safe area. The device is only flameproof once that closure is refitted correctly and undamaged, every time. Other designs are cemented permanently, so the user can never open them, not even for a SIM card. Either way, it is one more step in the safety chain that depends on people.
5. Heavier, quieter and harder to use
- Weight. Published figures for flameproof smartphone assemblies run from roughly 400 g to 750 g, much of it aluminium and glass added around a normal phone.
- Audio. Sound has to travel through the enclosure. Manufacturers of these enclosures commonly recommend a certified Bluetooth headset for calls, which is a further accessory to buy, charge and manage.
- Ports. USB and wired accessories cannot be used in the zone. Charging is wireless, or through an opening that may only be used outside the hazardous area.
- Touch and signal. The screen is used through an extra glass window, and some manufacturers note lower touch sensitivity with gloves or in wet conditions, and some loss of signal strength.
6. The battery is outside the flameproof test
Flameproof certification shows that an enclosure contains a gas explosion inside it. A lithium-ion cell in thermal runaway is a different event, because it produces its own gas and pressure and keeps burning. A 2025 NIOSH study notes that IEC 60079-1 does not currently include assessment criteria for lithium-ion thermal runaway. In that study, a large 429 Wh battery pack failed inside an approved explosion-proof enclosure for mining use, and the enclosure did not contain the event.
That test involved a mining battery, not a phone, and a phone battery stores far less energy. The point is about scope: the flameproof certificate addresses a gas explosion inside the housing, not a failing battery. In an intrinsically safe phone, the battery and its protection circuits are part of the assessment under IEC 60079-11, including under fault conditions.
7. Tied to one phone model
A flameproof certificate covers the specific phone models it names. Every new phone model needs its own enclosure work and certificate, so Ex versions arrive months after the consumer launch. Phone swaps and upgrades inside the enclosure are carried out by the manufacturer.
Side by side in Zone 1
| In daily use | Intrinsically safe phone (Ex ib) | Flameproof enclosure (Ex db) |
|---|---|---|
| Where the protection is | In the circuits and battery | In the enclosure: glass, joints, closures |
| The phone inside | Designed and assessed as a whole | Consumer smartphone, treated as a possible ignition source |
| A cracked screen or dented corner | Energy limits still in place; check per manual | Protection may be lost; leave the zone |
| Impact rating on glass | Typically a rugged handset design; drop resistance on the datasheet | Commonly a low limit, around 2 J |
| Repair | Certified repair route | Joints not repairable; back to the manufacturer |
| Weight | Phone weight only | Roughly 400 to 750 g, including the enclosure |
| Calls | Built-in speaker and microphone | Muffled; headset commonly recommended |
| Ports and accessories | Certified accessories as listed | No wired ports in the zone |
| Battery failure | Assessed under IEC 60079-11 | Not covered by flameproof test criteria |
A buyer's checklist for Zone 1 phones
- Read the marking, not the product name. The letters after "Ex" give the protection method: ib for intrinsic safety, db for a flameproof enclosure. Gb at the end means Zone 1.
- Check the certificate yourself on the IECEx online database. Confirm that it is current and names the exact model you are buying.
- Read the specific conditions of use whenever the certificate number ends in X. Look for impact limits, charging rules and opening rules.
- Ask what happens after a drop: who inspects the device, what counts as damage, who repairs it and how long that takes.
- Count the accessories. Headsets, chargers and holsters must be covered by the certification, and a phone that needs a headset for calls doubles the kit.
- Use only certified batteries and chargers, and charge outside the hazardous area unless the certificate says otherwise.
Frequently asked questions
Which is better for Zone 1, an intrinsically safe phone or a flameproof phone?
For most Zone 1 users, an intrinsically safe phone. Its protection is designed into the circuits and battery, so it does not depend on the housing staying intact. A flameproof phone is safe only while its enclosure is undamaged, its glass is commonly certified for low impact only, and the enclosure adds weight and limits audio and ports.
Is a smartphone in a flameproof enclosure legal in Zone 1?
Yes, when the assembly is certified for Zone 1 (equipment protection level Gb) and used as its certificate and the manufacturer's instructions require. Flameproof enclosure, Ex d, is a recognised protection method under IEC 60079-1.
What should happen after a flameproof phone is dropped?
Follow the manufacturer's instructions. A practical site rule is to inspect the windows, joints and corners after every drop, before the device goes back into the hazardous area, and to withdraw it if any damage is found. Many certificates state a low impact limit for the glass, and a slip from a pocket or hand can exceed it.
Can a damaged flameproof phone be repaired on site?
No. Certificates for these devices prohibit repair of the flameproof joints, and repair of Ex equipment is governed by IEC 60079-19. A damaged unit normally goes back to the manufacturer or an authorised facility.
Official sources
- IECEx online certificate database
- IECEx scheme
- IEC hazardous areas (Ex) overview
- Dubaniewicz, T. H. (2025), Explosion-Proof Enclosure Failure to Contain a Lithium-Ion Battery Thermal Runaway, Mining, Metallurgy & Exploration (NIOSH)
- European Commission: ATEX equipment
This article compares protection methods under the IEC 60079 series in general terms, based on publicly available certificates and standards. It does not refer to, assess or rate any particular product or manufacturer. For any given device, the certificate, its specific conditions of use and the manufacturer's instructions apply. Product and company names belong to their respective owners.