Why Zone Drives the Specification
Every camera installed in a hazardous area is constrained by the zone it sits in. Get the zone classification right and the rest of the specification follows in a predictable sequence. Get it wrong and the camera is either non-compliant, over-specified at significant cost, or rejected at site acceptance. Zone classification is the first decision in any hazardous area surveillance design, and it is almost always set by the safety case or the HAZID review long before procurement begins.
The job for the surveillance designer is to read the hazardous area drawing, identify the zone for each camera position, and select a camera with certifications that cover that zone, the relevant gas group, and the temperature class for the site. This article walks through that process and the supporting specifications that follow from it.
Zones, Divisions, and What They Mean
Two parallel classification systems are in common use. The IEC system, used internationally and the basis for ATEX and IECEx, defines zones for gas atmospheres. The North American system, defined in NEC Article 500, defines divisions. Most projects outside North America use the zone system, and most North American projects use either system depending on operator preference.
Zone 0 covers areas where an explosive gas atmosphere is present continuously or for long periods. Inside fuel tanks, vapour spaces, and certain enclosed process volumes. Cameras in Zone 0 must use intrinsically safe protection (Ex ia) or another method certified to the same level.
Zone 1 covers areas where an explosive atmosphere is likely to occur in normal operation. Around process equipment, pump rooms, compressor houses, and the cargo handling areas of LNG and oil vessels. Cameras in Zone 1 typically use flameproof (Ex db) or increased safety combined with flameproof (Ex de) protection.
Zone 2 covers areas where an explosive atmosphere is not likely in normal operation but may occur for a short period. Most open deck areas adjacent to process zones, ventilation outlets, and the inboard sides of accommodation blocks. Zone 2 cameras can use Ex tb dust protection, Ex nA non-sparking protection, or any higher protection method designed for Zone 1 or Zone 0.
In the North American system, Class I Division 1 corresponds roughly to Zone 0 plus Zone 1, and Class I Division 2 corresponds to Zone 2. The mapping is not exact, and project documentation should state explicitly which system is in use.
Gas Group and Temperature Class
Beyond zone, two further parameters drive certification. Gas group describes the explosive properties of the specific gases present. Group IIA covers propane and similar gases. Group IIB covers ethylene. Group IIC covers hydrogen and acetylene, the most demanding case. A camera certified for IIC is acceptable for IIB and IIA areas as well. A camera certified for IIC is acceptable in IIB and IIA areas as well, but a camera certified only for IIA cannot be used in a IIB or IIC area.
Temperature class describes the maximum surface temperature the camera can reach during operation. T1 corresponds to 450 degrees Celsius and T6 to 85 degrees Celsius. For most oil and gas installations, T4 (135 degrees Celsius) or T5 (100 degrees Celsius) is the relevant class. A T6 camera is acceptable in any T1 through T6 area, while a T4 camera cannot be used where T5 or T6 is required.
The full marking for a typical Zone 1 camera reads something like Ex db IIC T4 Gb. Each element matters and should be checked against the site hazardous area document before procurement.
Protection Methods Compared
Flameproof (Ex d, often labelled Ex db) is the most common method for Zone 1 cameras. The housing is built to contain any internal explosion and prevent ignition of the surrounding atmosphere. Flameproof housings are heavy, robust, and well suited to fixed installations where the camera is unlikely to be moved often.
Increased safety (Ex e, labelled Ex eb) prevents arcs and sparks during normal operation through enhanced construction techniques. Pure Ex e is rarely used for cameras since the electronics are difficult to certify under this method alone, but it is often combined with flameproof in an Ex de marking, where the camera body is flameproof and the cable termination compartment is increased safety.
Intrinsically safe (Ex i, labelled Ex ia or Ex ib) limits the energy in the circuit so that any spark or hot surface is incapable of igniting the surrounding gas. Cameras are rarely fully intrinsically safe due to the power required for image sensors and processing, but auxiliary equipment such as door switches and pushbuttons often uses this method.
Non-sparking (Ex n, labelled Ex nA or Ex ec in the current standard) covers Zone 2 only. It relies on the lower probability of an explosive atmosphere combined with construction features that minimise arcing and sparking, and it is usually the most cost-effective choice for Zone 2 installations.
Housings, Glands, and Accessories
The certification covers the camera as a complete unit. Replacing the housing, the cable gland, or the bracket with a non-certified component invalidates the certification. This is the single most common cause of failed site acceptance audits.
Cable glands must match the protection method and the cable type. A flameproof gland for armoured cable is not the same as one for unarmoured cable, and a gland rated for IIB is not acceptable in a IIC area. The gland marking should appear in the project documentation alongside the camera marking.
Mounting brackets, junction boxes, and any auxiliary devices fitted to the camera must carry their own certifications consistent with the zone. Bergen Security supplies certified accessories matched to its explosion-proof cameras, which avoids mismatched components at site.
Reading a Certificate
Every certified camera comes with a certificate from a notified body such as DEKRA, SGS Baseefa, UL, or LCIE. The certificate confirms the marking, the protection method, the gas groups, the temperature class, and any specific conditions of use. The conditions of use are easily overlooked and frequently relevant. A common condition is that the camera must be installed in accordance with a specific document or manufacturer instruction, or that certain ambient temperature ranges apply. Reading the conditions of use before procurement avoids site issues later.
Maintenance and Recertification
An explosion-proof camera is not a fit-and-forget device. The certification depends on the camera being maintained in the condition that the certification covers. A loose flameproof joint, a damaged gland, a missing gasket, or an unauthorised modification to the wiring all invalidate the certification, and any of these can pass unnoticed without a maintenance routine that looks for them.
Routine inspection of hazardous area equipment is defined by IEC 60079-17 and the equivalent national standards. The frequency depends on the protection method and the operating environment, but most installations require a visual inspection at least once per year and a close inspection every three years. The records of these inspections are part of the project safety file and may be checked by the regulator during an audit.
Recertification of the equipment is a different matter from inspection. If a camera is modified during operation, repaired with non-certified parts, or moved to a higher zone, the original certification no longer applies, and the device must be recertified. The cost of recertification is high enough that the operational rule is usually to specify cameras for the worst zone they will ever encounter and avoid modifications during the life of the installation.
Matching the Camera to the Hazardous Area
Selecting an explosion-proof camera means matching several parameters to the position it will occupy: the zone, the gas group, the temperature class, the ingress protection rating for the environmental exposure, the housing material (stainless steel grade or marine grade aluminium), the resolution, frame rate, and sensor type for the surveillance task, and any integrated functions such as analytics, illumination, or PTZ. What makes this systematic rather than guesswork is that each parameter comes from a known source. Zone and gas group come from the safety case, the environmental requirements from the site environmental data, and the surveillance function from the operational philosophy.
Documentation is part of the package too, and it matters as much as the hardware. A certified camera normally arrives with the certificate of conformity from the notified body, the manufacturer declaration of conformity, the test reports for any specific tests called up in the certificate, and the installation and maintenance manual. When any of this is missing or incomplete, the camera can stall at site acceptance even if the unit itself is correct, which is why the paperwork is treated as seriously as the specification.
Explosion-proof camera selection is a systematic check of the camera certification against the site requirements, followed by an environmental and operational specification consistent with the certification. The decisions are made in a specific order, and skipping any step almost always leads to rework.
For most oil and gas projects, the right approach is to develop the camera schedule alongside the hazardous area drawings, with input from the safety engineer at every stage. The cost difference between an Ex db IIC T4 camera and an Ex db IIB T4 camera is small. The cost of installing the wrong one and replacing it during commissioning is substantial.
