Positive Pressure Containers: Protecting Critical Equipment in Hazardous Areas

Summary

A positive pressure container protects personnel and equipment by maintaining the internal pressure above the surrounding atmosphere, so airflow moves outward through controlled leakage paths rather than allowing external gas, vapour or dust to enter. It is commonly used for offshore laboratories, mud logging cabins, control rooms and MCC or switchgear shelters.

Pressure alone is not a complete specification. A reliable solution must integrate the enclosure, clean-air source, purge and pressurization system, HVAC, gas detection, alarms, shutdown logic, fire protection, electrical equipment, cable and pipe penetrations, doors and host-facility interfaces. The correct design depends on the hazardous-area classification, internal equipment, process releases, installation location and required certification.

What Is a Positive Pressure Container?

A positive pressure container is an enclosed module supplied with clean air at a rate that keeps its internal pressure higher than the external atmosphere. When the enclosure is intact, the pressure differential establishes outward airflow at doors, seals and other defined leakage paths. This helps prevent a hazardous external atmosphere from entering the protected space.

The system is useful when equipment that is suitable for operation in a clean or safe internal environment must be installed near flammable gas, vapour or dust hazards. Typical applications include:

MCC, switchgear, MCP, VFD and VSD shelters;
offshore laboratories and mud logging cabins;
control, instrumentation and monitoring rooms;
workshops and equipment cabins; and
other occupied or equipment modules located in a project-defined hazardous area.

TLS manufactures standard and customized pressurized modules for offshore and onshore projects. The protective concept, equipment selection and certification scope must nevertheless be established for each installation.

How Does the Protection System Work?

The operating sequence normally begins with a purge using air from a verified safe source. The purge replaces the initial internal atmosphere before equipment that depends on pressurization is energized. The system then maintains the required pressure and monitors whether the protected condition remains valid.

A project-specific control philosophy may include:

confirmation that doors and access points are closed;
verification that the air source and airflow are available;
a timed or volume-based purge before energization;
continuous pressure monitoring during operation;
external gas detection at the fresh-air intake and other defined locations;
alarms if pressure, airflow or gas conditions move outside permitted limits; and
automatic isolation, ventilation response or power shutdown according to the risk assessment.

The exact sequence cannot be selected from container size alone. Required purge volume, minimum pressure, leakage allowance, alarm delays and shutdown actions must be defined against the applicable protection concept and project requirements. The IEC 60079 series provides the international framework for equipment and installations in explosive atmospheres; the precise parts and edition must be stated in the project specification.

Why Is Pressurization Not Enough by Itself?

Positive pressure primarily addresses an external hazard: it helps prevent a hazardous atmosphere outside the module from reaching equipment and personnel inside. It does not remove a flammable or toxic substance released within the module.

This distinction is especially important in laboratories and mud logging cabins. Samples, chemicals, process lines or equipment can create an internal release even when the room is successfully pressurized. Depending on the hazard assessment, the design may therefore require:

an explosion-proof fume hood or local extraction system;
dedicated exhaust connections for safety cabinets or process equipment;
internal detection for gases such as methane or hydrogen sulphide;
Ex-rated electrical equipment where ignition risk remains;
emergency ventilation and shutdown functions;
segregation of hazardous work from clean equipment areas; and
fire detection, emergency lighting, an emergency stop and safe escape provisions.

The clean-air pressurization system and the process exhaust system must be balanced as one ventilation design. Excessive extraction can collapse positive pressure, while insufficient extraction can allow an internal contaminant to accumulate. Airflow calculations and control logic must cover normal operation, door opening, equipment extraction and emergency conditions.

What Can a TLS Positive Pressure Module Include?

TLS brochure configurations show that the final module can combine structural, safety and operational systems. Depending on the agreed scope, a positive pressure container may include:

a DNV 2.7-1/EN 12079 offshore container structure or an ISO/CSC transport configuration;
A-0 or A-60 fire-rated boundaries where required;
an airlock or controlled access arrangement;
a combined pressurization, fire and gas control panel;
pressure switches, flow monitoring, solenoid valves and loss-of-pressure alarms;
gas and smoke detectors;
fail-safe fire dampers;
HVAC designed for the occupancy and equipment heat load;
Ex-approved external or internal electrical components as required;
emergency lighting, fire extinguishers, emergency stops and an escape hatch;
MCT frames or other certified cable and pipe transit systems; and
fast-plug electrical and utility interfaces.

These are available features, not a universal standard package. Each item must be confirmed in the quotation, drawings and certification scope.

How Do Laboratory and MCC Shelter Requirements Differ?

Positive pressure laboratory or mud logging cabin

A laboratory is an occupied process space. Its design must address personnel safety, chemical compatibility, sample handling, water and drainage, furniture, work surfaces, fume extraction, lighting, communications and emergency response in addition to pressurization.

TLS brochure examples include laboratory configurations with resistant workbenches, sinks, storage, fume hoods, eye wash equipment, fire and gas detection, HVAC and connections to host utilities. A reference mud logging cabin is shown as a 20ft module with DNV 2.7-1/EN 12079 structural rating, A-60 protection and Zone 1/Zone 2-related systems. These details describe particular configurations and should not be assumed for every laboratory.

MCC or switchgear pressurized shelter

An MCC shelter is primarily an engineered environment for electrical assets and maintenance access. The internal layout is driven by the customer's MCC, switchgear, PLC, VFD/VSD and auxiliary equipment. Critical inputs include heat dissipation, arc-flash boundaries, cable entry, floor loading, working clearances, replacement routes and maintainability.

TLS offers nominal 15ft, 20ft and 40ft shelter formats as well as custom dimensions. Positive pressure, HVAC and fire-and-gas functions protect the internal operating environment, while the customer and equipment supplier must still define panel ratings, electrical protection, arc-flash controls and installation requirements. The shelter supports the electrical equipment; it does not replace its own safety design.

What Do DNV 2.7-1, IEC 60079 and A-60 Cover?

These requirements address different risks and should not be treated as interchangeable certificates.

DNV 2.7-1 and EN 12079

DNV-ST-E271, commonly called DNV 2.7-1, addresses offshore container design, manufacture, testing, marking, inspection and lifting sets. EN 12079 is also widely specified for offshore containers. These requirements establish offshore structural and handling capability; they do not alone approve the pressurization, fire protection or hazardous-area concept.

IEC 60079

The IEC 60079 series addresses equipment and installations in explosive atmospheres. The applicable part, protection concept, equipment protection level, gas or dust group, temperature class, zone and certification basis must be defined. A general statement such as “Zone 1/Zone 2 suitable” is not sufficient without the exact design and approval scope.

A-60 fire protection

A-60 addresses fire integrity and insulation performance of the specified boundary assembly under prescribed test conditions. Walls, roof, floor, doors, dampers, penetrations and joints must preserve the required boundary. A-60 does not certify hazardous-area protection or offshore lifting.

What Should Buyers Define Before Requesting a Quotation?

Provide the following information at the enquiry stage:

Application: laboratory, mud logging, control room, MCC, switchgear or another function.
Installation: offshore platform, vessel, FPSO, onshore plant or other host facility, including the exact proposed location.
Hazardous-area basis: zone, gas or dust group, temperature class, external hazards and applicable client standards.
Internal release sources: samples, chemicals, process lines, batteries or equipment that can release gas, vapour, heat or dust.
Certification: DNV 2.7-1/EN 12079, CSC, IECEx, ATEX, class approval, A-0/A-60 or other stated requirements.
Clean-air source: location, quality, duct route, available pressure and the method used to confirm that the intake remains safe.
Pressurization logic: purge sequence, pressure set points, alarm levels, door status, gas detection, shutdown and recovery philosophy.
HVAC and extraction: ambient conditions, occupancy, equipment heat load, required internal conditions, fume hood or process exhaust and redundancy.
Electrical interfaces: voltage, frequency, connected loads, fault level, earthing, cable entries, socket standard and Ex requirements.
Equipment data: dimensions, weights, heat loads, access clearances, maintenance routes and cable schedules for customer-supplied equipment.
Fire and safety systems: fire and smoke detection, suppression interfaces, emergency stop, emergency lighting, escape and host alarms.
Transport and installation: dimensions, weight limits, lifting set, deck loading, tie-down, stacking and access restrictions.
Testing and documents: calculations, drawings, certificates, inspection plan, FAT scenarios and commissioning responsibilities.

Frequently Asked Questions

Does positive pressure make all internal equipment explosion-proof?

No. Pressurization can form part of a hazardous-area protection strategy, but the complete system must be engineered, controlled and certified for the intended application. Equipment exposed during loss of pressure, purge, maintenance or an internal release may require additional protection.

Can a positive pressure laboratory contain hazardous chemicals generated inside?

Not by pressure alone. Positive pressure drives air outward and is mainly used to exclude external contamination. Internal hazardous releases normally require local exhaust, treatment, detection, suitable electrical equipment and emergency logic based on the process risk assessment.

Is every TLS pressurized container DNV 2.7-1 and A-60 certified?

No. TLS can supply configurations with these requirements, but certification and fire rating must be specified and confirmed for the exact project and module.

Can an MCC shelter use non-Ex switchgear?

Potentially, if the complete pressurized-room protection concept permits it and all operating, purge, alarm and failure conditions are addressed. The decision must be made by the responsible hazardous-area engineering and certification parties, not assumed from the enclosure alone.

What is the most important early design decision?

Define whether the main hazard is outside the module, inside the module or both. That decision determines whether positive pressure is appropriate and what extraction, detection, equipment protection and interlocks are also required.

Request a Project-Specific Positive Pressure Container Review

TLS Offshore Containers supplies pressurized laboratories, mud logging cabins, MCC and switchgear shelters, control modules and other customized containerized solutions. Send TLS your application, hazardous-area classification, internal equipment, release sources, required certification, ambient conditions, electrical supply, HVAC loads, utility interfaces and target delivery schedule.

Contact TLS Offshore Containers to request a preliminary technical review or quotation.