Explosion-proof camera coverage planning determines how many cameras are needed, where to place them, and which lens focal lengths provide adequate coverage. The key variables are the required monitoring task (detection vs. identification), the field of view angle at the required distance, zone geometry, and whether PTZ cameras can consolidate coverage of multiple areas. Most industrial process facilities require one fixed camera per critical asset plus perimeter coverage at 15-25 meter intervals.
Unlike standard commercial CCTV, explosion-proof camera systems cannot be repositioned easily once installed. Conduit runs are sealed, housings are bolted to rated junction boxes, and repositioning requires hot-work permits and reclassification confirmation. Getting camera placement right during the design phase saves significant cost and avoids coverage gaps that cannot be corrected without major rework. This guide walks through the coverage planning process from zone map to final camera count.
Step 1: Define the Monitoring Task for Each Zone
Coverage requirements differ depending on what the camera must accomplish. Security and safety camera applications use four standard monitoring tasks, each requiring a different pixel density at the target:
Detection (20 pixels/meter): Confirming that a person or object is present. Suitable for perimeter monitoring of large open areas. Observation (40 pixels/meter): Distinguishing the activity of a person (walking, operating equipment). Suitable for process area entry monitoring. Recognition (80 pixels/meter): Identifying whether a person is familiar or a stranger. Suitable for gate access monitoring. Identification (160 pixels/meter): Identifying a specific individual or reading a license plate. Required for security-critical choke points.
For a 2MP camera (1920×1080 resolution) with a 90-degree horizontal field of view, the horizontal coverage at detection level is approximately 96 meters. At identification level, the same camera covers approximately 12 meters. Selecting the monitoring task before choosing lenses prevents under- or over-specifying coverage at the design stage.
Step 2: Map Classified Zones and Critical Assets
Start with the area classification drawing — the document produced during the hazardous area classification study that defines the boundaries of Class I Division 1/2, Zone 1/2, or equivalent areas. For each classified zone, identify the critical assets that must be monitored: compressor inlets, flare stacks, loading arms, valve manifolds, process vessel access points, and facility perimeter segments.
Camera positions must be compatible with the zone they are installed in. A camera placed inside a Zone 1 area must be rated for Zone 1 (ATEX Category 2G or Class I Division 1). A camera positioned just outside a Zone 2 boundary, in an unclassified area, can be a standard industrial camera — but its view must reach into the classified area without obstruction. Planning camera positions relative to zone boundaries allows you to minimize the number of certified explosion-proof cameras required without sacrificing coverage. For zone classification fundamentals, see our hazardous location classification guide.
Step 3: Select Lens Focal Length for Required Coverage Distance
| Focal Length | Approx. Horiz. FOV | Detection Distance (2MP) | Identification Distance (2MP) | Typical Use |
|---|---|---|---|---|
| 2.8 mm | ~100° | ~100 m | ~12 m | Small room, junction box area |
| 4 mm | ~80° | ~130 m | ~16 m | Process area general coverage |
| 8 mm | ~40° | ~260 m | ~33 m | Loading dock, gate, medium-range |
| 12 mm | ~27° | ~400 m | ~50 m | Flare stack base, long corridor |
| 25+ mm (telephoto) | ~12° or less | >800 m | ~100 m | Perimeter fence line, tank farm overview |
Step 4: Fixed vs. PTZ Camera Strategy
Fixed cameras provide continuous, uninterrupted coverage of a defined area. PTZ (pan-tilt-zoom) cameras can cover a much larger area but only monitor one direction at a time. For explosion-proof installations, the choice affects both camera count and total system cost significantly.
A general rule: use fixed cameras for all safety-critical and continuously monitored positions, and PTZ cameras for operator-directed surveillance of large open areas. A PTZ camera covering a 200-meter tank farm perimeter might replace 8-10 fixed cameras, but if the PTZ is positioned on an intruder’s approach route, the intruder may pass undetected during the few seconds the camera is pointing elsewhere. Most facilities use a combination: fixed cameras at zone boundaries, entry points, and critical assets, with PTZ cameras for general area surveillance and incident investigation zoom capability. For a complete system design walkthrough, see our hazardous area CCTV system design guide.
Step 5: Coverage Density by Facility Type
Coverage requirements vary significantly by facility type and regulatory framework. The following benchmarks are derived from common industry practice and do not replace site-specific risk assessment:
Oil and gas refinery process areas: One fixed camera per major process unit entry point (compressor inlet, separator, heat exchanger block), plus perimeter coverage at 20-25 meter intervals along classified zone boundaries. A mid-sized refinery unit (distillation column block) typically requires 8-14 cameras. Chemical plant process areas: Higher camera density due to proximity of workers during normal operations. One camera per reactor zone access point, with 15-20 meter perimeter spacing. Offshore platform deck: Every major deck level should have at least two cameras with overlapping coverage; lifeboat stations and emergency muster points require continuous fixed coverage. Mine surface plant: Crusher hall, conveyor transfer points, and loading station each require dedicated fixed cameras; general yard coverage with PTZ is common.
Frequently Asked Questions
How many explosion-proof cameras do I need for a small process facility?
A small process facility typically requires 8-16 cameras: one per critical asset, two at each entry gate, and perimeter cameras at 20-25 meter intervals. PTZ cameras can reduce count for open yard areas.
What focal length for outdoor hazardous area cameras?
For 20-50 meter coverage, use a 4mm lens. For 50-100 meters, 8mm or 12mm. Varifocal lenses (e.g., 2.8-12mm motorized) allow adjustment during commissioning.
Can a PTZ replace multiple fixed cameras in Zone 1?
PTZ cameras reduce count but sacrifice continuous coverage. For safety-critical positions, fixed cameras are preferred. PTZ cameras are best used for operator-directed surveillance and incident investigation, not as the primary safety camera on a critical asset.
How much overlap is needed between cameras?
A 15-20% field of view overlap eliminates dead zones, accounts for positioning tolerances, and provides redundancy if one camera fails. On perimeter lines, 20% overlap is recommended.
Can I place a non-rated camera just outside the classified zone?
Yes. If a standard industrial camera positioned outside the zone boundary has a clear line of sight into the classified area and meets the coverage task requirements, it may replace an explosion-proof camera at that position. This is a common cost-reduction strategy — verify zone boundary positions carefully before finalizing placement.
Veilux provides system design support including camera count estimates, lens selection, and zone boundary review for new installations. Contact our team with your facility plan and classified zone drawing to get a preliminary camera layout.
Key Industry Standards and References
Security system design guidance is in NFPA 730 (Guide for Premises Security). Hazardous area installation requirements are in NFPA 70 (NEC) and IEC 60079-14.
Related Resources
- Explosion-Proof Camera Selection Guide
- Explosion-Proof Camera Housing Selection Guide
- Explosion-Proof Camera Lens Selection Guide
- NVR Selection for Explosion-Proof CCTV Systems
- How to Design a Hazardous Area CCTV System
- Request a Project Quote
Need explosion-proof cameras for your facility?
Veilux has designed and supplied explosion-proof surveillance systems for oil refineries, chemical plants, offshore platforms, grain elevators, and mining operations. Our engineers review your hazardous area classification and specify certified cameras that meet every code requirement.
About the Author
Daniel Fernandez
Daniel Fernandez is a hazardous area security systems specialist with over a decade of experience specifying ATEX, IECEx, UL Class I Division 1, and cUL certified surveillance equipment for oil and gas, chemical, mining, pharmaceutical, and offshore environments. He holds expertise in NEC and IEC area classification standards and has consulted on explosion-proof camera system designs across North America, Europe, and the Middle East.