Zone 0, Zone 1 & Zone 2 are among the most frequently used terms in hazardous area engineering, yet they are also some of the most misunderstood. Engineers, maintenance personnel, procurement teams, and even experienced industry professionals often assume these zones indicate the severity of an explosion. In reality, hazardous area zones do not measure how dangerous an explosion would be. Instead, they classify how often an explosive atmosphere is expected to be present.
Understanding the difference between Zone 0, Zone 1 & Zone 2 is essential for selecting suitable electrical equipment, designing safe installations, complying with IEC 60079 standards, and reducing the risk of fires and explosions in industrial facilities.
Whether you work in an oil refinery, pharmaceutical manufacturing plant, chemical processing facility, fuel storage terminal, hydrogen installation, or any industry handling flammable materials, understanding hazardous area zones helps ensure that equipment is installed safely and operated within its intended environment.
Incorrect interpretation of hazardous zones can result in unsuitable equipment selection, increased maintenance costs, regulatory non-compliance, and, in the worst cases, catastrophic industrial incidents.
In this guide, we explain what Zone 0, Zone 1, and Zone 2 mean, how they are determined, where they are commonly found, and how they influence the selection of explosion-protected equipment.
Quick Answer: What Are Zone 0, Zone 1 & Zone 2?
Zone 0, Zone 1, and Zone 2 are hazardous area classifications defined by the IEC 60079 series of standards. They indicate the likelihood and duration of an explosive gas atmosphere being present.
- Zone 0: An explosive atmosphere is present continuously, frequently, or for long periods.
- Zone 1: An explosive atmosphere is likely to occur during normal operation.
- Zone 2: An explosive atmosphere is not expected during normal operation and, if it occurs, will exist only for a short duration.
These classifications help engineers determine which explosion-protected equipment is suitable for each location and form the basis of safe electrical and mechanical system design.
For a broader understanding of how hazardous locations are identified and assessed, read our guide on Hazardous Area Classification (HAC).
What Are Zone 0, Zone 1 & Zone 2?
Hazardous area zones are a method of classifying locations where flammable gases or vapours may mix with air and create an explosive atmosphere.
Instead of treating an entire facility as hazardous, engineers identify only those locations where explosive atmospheres are reasonably expected to occur. This allows organisations to apply appropriate engineering controls while avoiding unnecessary costs associated with over-specifying equipment.
Hazardous area zones are determined during a Hazardous Area Classification (HAC) study, which evaluates factors such as:
- Properties of the flammable material
- Frequency of release
- Duration of release
- Ventilation conditions
- Operating pressure and temperature
- Process equipment configuration
- Potential ignition sources
The resulting zone classification helps define where explosion-protected equipment is required and which protection concept is appropriate for each area.
It is important to note that Zone 0, Zone 1, and Zone 2 apply only to flammable gases and vapours. Facilities handling combustible dust use a different classification system consisting of Zone 20, Zone 21, and Zone 22. If your operations involve pharmaceutical powders or other combustible dusts, read our guide on Magnesium Stearate: A Hidden Dust Explosion Hazard in Pharmaceutical Manufacturing to understand how combustible dust can create explosion risks during routine processing.
Why Are Zone 0, Zone 1 & Zone 2 Important?
Not every location where flammable materials are handled presents the same level of risk.
For example, the inside of a petrol storage tank contains flammable vapours almost continuously, whereas an area several metres away from the tank may only become hazardous if an accidental leak occurs.
Treating both locations as equally hazardous would result in unnecessary costs and impractical engineering designs. Conversely, treating every location as low risk could expose personnel and equipment to serious explosion hazards.
Dividing hazardous locations into zones enables engineers to:
- Select equipment appropriate for the actual level of risk.
- Improve electrical and mechanical safety.
- Reduce unnecessary project costs.
- Comply with international standards.
- Prevent ignition of explosive atmospheres.
This risk-based approach has become the global standard for hazardous area engineering and is widely adopted across industries handling flammable gases and vapours.
Zone 0, Zone 1 & Zone 2 Explained: What is Zone 0?
Zone 0 is the highest classification within Zone 0, Zone 1 & Zone 2 hazardous area zoning. According to IEC 60079-10-1, Zone 0 is an area where an explosive atmosphere consisting of a mixture of air and flammable gases or vapours is present continuously, for long periods, or frequently during normal operation.
Because an explosive atmosphere is expected to exist for extended durations, only equipment specifically designed and certified for Zone 0 applications may be installed in these locations.
Typical examples of Zone 0 include:
- Inside fuel storage tanks
- Inside solvent vessels
- Internal sections of process reactors
- Vapour spaces within storage equipment
- Certain enclosed sections of process pipelines
In these environments, the presence of flammable gas is considered a normal operating condition rather than an abnormal event.
For this reason, equipment installed in Zone 0 must provide the highest level of explosion protection.
Intrinsic Safety (Ex ia) is one of the most widely used protection concepts for Zone 0 because it limits electrical energy below the minimum ignition energy of the surrounding atmosphere.
Unlike Flameproof (Ex d) equipment, which safely contains an internal explosion, Intrinsic Safety prevents ignition from occurring in the first place. To better understand these protection concepts, read our guide on ATEX vs Flameproof.
Practical Example
Consider a large ethanol storage tank used in a pharmaceutical manufacturing facility.
The vapour space inside the tank contains a flammable ethanol-air mixture almost continuously. Since an explosive atmosphere exists during normal operation, the interior of the tank is classified as Zone 0.
Any instrumentation installed inside the tank, such as level transmitters or temperature sensors, must be certified for Zone 0 service using an appropriate explosion protection concept.
Key Characteristics of Zone 0
| Parameter | Zone 0 |
|---|---|
| Explosive atmosphere | Continuously, frequently, or for long periods |
| Risk level | Highest probability of occurrence |
| Typical locations | Tank interiors, process vessels, enclosed equipment |
| Common protection concept | Ex ia (Intrinsic Safety) |
| Applicable standard | IEC 60079-10-1 |
Zone 0, Zone 1 & Zone 2 Explained: What is Zone 1?
Within Zone 0, Zone 1 & Zone 2 hazardous area classifications, Zone 1 refers to an area where an explosive atmosphere is likely to occur during normal operation, although it is not present continuously.
Zone 1 is the most commonly encountered hazardous area in facilities handling flammable gases or vapours.
During routine operations such as filling, draining, pumping, sampling, or venting, small quantities of flammable material may be released into the surrounding atmosphere. When these releases are expected as part of normal plant operations, the surrounding area is generally classified as Zone 1.
Unlike Zone 0, where hazardous atmospheres are continuously present, Zone 1 only becomes hazardous when normal process activities create a release.
Typical examples include:
- Around pump seals
- Tank vent outlets
- Sampling points
- Loading and unloading stations
- Compressor seals
- Process flanges
- Valve assemblies
- LPG filling manifolds
Equipment installed in Zone 1 must remain safe whenever an explosive atmosphere is likely to develop.
Common protection concepts include:
- Ex d (Flameproof)
- Ex e (Increased Safety)
- Ex p (Pressurization)
- Ex ib (Intrinsic Safety)
The most suitable protection method depends on the application, gas group, temperature class, and equipment design.
Practical Example
Consider an LPG bottling plant.
During cylinder filling operations, small quantities of LPG may be released around the filling manifold as part of normal production. Since these releases are expected during normal operation, the surrounding area is classified as Zone 1.
Electrical motors, lighting fixtures, junction boxes, and instrumentation installed within this area must be certified for Zone 1 applications.
Zone 0, Zone 1 & Zone 2 Explained: What is Zone 2?
Among the Zone 0, Zone 1 & Zone 2 classifications, Zone 2 represents locations where an explosive atmosphere is not expected during normal operation. If a release does occur, it is likely to exist only for a short period before dispersing.
Zone 2 should not be considered a safe area. Rather, it indicates that the probability of an explosive atmosphere forming is significantly lower than in Zone 0 or Zone 1.
These areas are commonly located beyond Zone 1 boundaries, particularly where effective natural or mechanical ventilation rapidly disperses any accidental release.
Typical Zone 2 locations include:
- Areas surrounding process equipment
- Outdoor pump installations
- Around storage tanks with effective ventilation
- Adjacent process pipework
- Fuel dispensing forecourts
- Well ventilated chemical storage areas
Because explosive atmospheres are only expected during abnormal situations such as equipment failure or accidental leakage, Zone 2 equipment requirements are generally less restrictive than those for Zone 1.
Common protection concepts include:
- Ex ec
- Ex n (legacy installations)
- Certain Ex d and Ex e equipment where applicable
Practical Example
A diesel or petrol storage terminal may classify the immediate area around a tank vent as Zone 1, while the surrounding well ventilated area is classified as Zone 2 because flammable vapours would only be present briefly following an abnormal release.
Zone 0 vs Zone 1 vs Zone 2
| Feature | Zone 0 | Zone 1 | Zone 2 |
|---|---|---|---|
| Probability of explosive atmosphere | Continuous or frequent | Likely during normal operation | Unlikely during normal operation |
| Duration | Long periods | Occasional | Short duration |
| Typical examples | Tank interiors, reactors | Pump seals, loading arms, vents | Surrounding well-ventilated process areas |
| Typical protection methods | Ex ia | Ex d, Ex e, Ex p, Ex ib | Ex ec, Ex d, Ex e (as applicable) |
Industrial Examples of Zone 0, Zone 1 & Zone 2
Hazardous area zones vary depending on the process and facility design.
Some common examples include:
| Equipment or Location | Typical Zone |
|---|---|
| Inside a petrol storage tank | Zone 0 |
| Tank vent outlet | Zone 1 |
| LPG cylinder filling manifold | Zone 1 |
| Pump mechanical seal | Zone 1 |
| Around loading gantries | Zone 1 or Zone 2 |
| Outdoor process area with effective ventilation | Zone 2 |
| Fuel dispensing area | Zone 2 |
These examples are indicative only. Actual zone classification should always be determined through a formal Hazardous Area Classification study conducted in accordance with applicable standards.
Equipment Selection for Zone 0, Zone 1 & Zone 2
Once hazardous zones have been identified, engineers must select equipment that matches the classification.
Equipment selection should consider:
- Hazardous zone
- Gas group
- Temperature class
- Equipment Protection Level (EPL)
- Applicable explosion protection concept
Selecting equipment based solely on labels such as “Explosion Proof” or “ATEX Certified” without reviewing the complete Ex marking is a common mistake that can lead to non-compliance and increased safety risks.
Understanding both the hazardous zone and the equipment certification is essential for safe and reliable industrial operations.
Common Mistakes When Working in Zone 0, Zone 1 & Zone 2
Understanding the difference between Zone 0, Zone 1, and Zone 2 is only the first step. Many industrial incidents occur because hazardous zones are misunderstood or equipment is selected based on assumptions rather than engineering requirements.
Below are some of the most common mistakes encountered during hazardous area classification and equipment selection.
1. Assuming Zone 2 Is Completely Safe
A common misconception is that Zone 2 is a “safe area.”
In reality, Zone 2 is still classified as a hazardous location. The difference is that an explosive atmosphere is unlikely to occur during normal operation and, if it does occur, it is expected to exist only for a short period.
Equipment installed in Zone 2 must still comply with the applicable explosion protection requirements.
2. Selecting Equipment Based Only on “ATEX Certified”
Many procurement teams purchase equipment simply because the product catalogue states that it is ATEX Certified.
However, ATEX certification alone does not indicate whether the equipment is suitable for Zone 0, Zone 1, or Zone 2.
Engineers should always verify:
- Ex protection concept
- Equipment Protection Level (EPL)
- Gas Group
- Temperature Class
- Zone suitability
Our article on ATEX vs Flameproof explains why certification and protection methods should never be confused.
3. Ignoring Ventilation
Ventilation plays an important role in hazardous area classification.
Effective ventilation can reduce the extent of hazardous zones by dispersing flammable gases before they accumulate to explosive concentrations.
Conversely, poor ventilation may increase the size of hazardous zones and require more extensive explosion-protected equipment.
4. Failing to Review Hazardous Zones After Plant Modifications
Hazardous Area Classification is not a one-time activity.
Whenever facilities undergo modifications such as:
- New equipment installation
- Process changes
- Increased production capacity
- Additional storage tanks
- New chemicals
- Changes in ventilation
the hazardous zones should be reassessed to ensure they continue to reflect actual operating conditions.
Best Practices for Working in Hazardous Areas
Facilities handling flammable gases or vapours should adopt the following best practices:
- Conduct a Hazardous Area Classification study before installing equipment.
- Select equipment that matches the hazardous zone, gas group, and temperature class.
- Verify the complete Ex marking rather than relying on marketing descriptions.
- Maintain accurate hazardous area drawings and documentation.
- Review hazardous zones whenever significant process changes occur.
- Train maintenance and operations personnel to understand hazardous area requirements.
- Inspect explosion-protected equipment periodically in accordance with applicable standards.
These practices help improve personnel safety, reduce operational risks, and maintain compliance with recognised engineering standards.
FAQs About Zone 0, Zone 1 & Zone 2
1. What is the difference between Zone 0, Zone 1 & Zone 2?
The difference lies in the likelihood of an explosive atmosphere being present.
- Zone 0: Present continuously or for long periods.
- Zone 1: Likely during normal operation.
- Zone 2: Unlikely during normal operation and present only for short durations if it occurs.
2. Which industries use Zone 0, Zone 1 & Zone 2 classifications?
These classifications are commonly used in:
- Oil and Gas
- Chemical Manufacturing
- Pharmaceutical Manufacturing
- Hydrogen Facilities
- Fuel Storage Terminals
- Paint Manufacturing
- Food Processing
- Battery Manufacturing
3. Which standard defines Zone 0, Zone 1 & Zone 2?
Hazardous area zones are defined by the IEC 60079-10-1 standard for explosive gas atmospheres.
In India, engineers commonly refer to the IS/IEC 60079 series.
4. Can hazardous zones change over time?
Yes.
Process modifications, equipment changes, ventilation improvements, or the introduction of new flammable materials may change hazardous zone boundaries.
Hazardous Area Classification studies should therefore be reviewed whenever significant modifications are made.
5. Is Flameproof equipment required in every hazardous zone?
No.
The appropriate protection concept depends on the hazardous zone and the application.
Depending on the equipment, engineers may select Ex ia, Ex d, Ex e, Ex p, Ex ec, or other recognised protection methods.
Conclusion
Understanding Zone 0, Zone 1 & Zone 2 is fundamental to designing safe industrial facilities and selecting appropriate explosion-protected equipment.
Rather than measuring the severity of an explosion, these hazardous area zones indicate how frequently an explosive atmosphere is expected to occur. This information enables engineers to choose suitable protection concepts, reduce ignition risks, and comply with internationally recognised standards such as IEC 60079.
Correct interpretation of hazardous area zones is essential for industries handling flammable gases and vapours, including oil and gas, chemical manufacturing, pharmaceuticals, fuel storage, and hydrogen production.
A well-executed Hazardous Area Classification study, combined with appropriate equipment selection and regular review, plays a vital role in protecting people, assets, and business continuity.
References
- IEC 60079-10-1: Explosive Atmospheres – Classification of Areas
- IEC 60079 Series
- IS/IEC 60079 Series (Bureau of Indian Standards)
- ATEX Directive 2014/34/EU
- NFPA 497 – Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapours