Emergency Vents & Manway Covers

Last-resort overpressure relief and safe tank access.

What It Is & How It Works

Emergency vents and manway covers are tank-mounted protection and access devices that address two distinct requirements at the tank shell. Emergency vents provide large-volume pressure relief during abnormal conditions, primarily external fire exposure, that generate vapor faster than conservation vents can discharge. Manway covers provide gas-tight personnel access to the tank interior for inspection, cleaning, and maintenance.

Emergency vents open when internal pressure exceeds a preset threshold, lifting a weighted pallet or cover to discharge vapor rapidly and prevent structural failure of the tank shell or roof-to-shell joint. Once the overpressure condition subsides, the pallet reseats to restore vapor containment. manhole covers seal the tank opening under normal conditions using bolted closures or the Expanda-Seal™ mechanism, which provides a gas-tight seal that operators can open and close without special tools.

Both device types mount directly to tank shell or roof nozzles and are sized to the tank diameter, design pressure, and applicable fire-case venting calculations per API 2000 and NFPA 30. Emergency vent sizing must account for the total fire-case vapor generation rate, while manhole sizing follows standard personnel access requirements for the vessel type.

Emergency Vent vs. Conservation Vent

Conservation vents manage normal tank breathing caused by thermal changes, liquid movement, and pumping operations. Emergency vents handle abnormal events, primarily fire exposure, that overwhelm a conservation vent’s capacity. Most fixed-roof tanks require both: a conservation vent for daily operations and an emergency vent for fire-case protection. Conservation vents control emissions; emergency vents prevent structural failure.

When to Specify Emergency Vents & Manway Covers

Emergency vents and manway covers are specified when a storage tank requires fire-case overpressure protection or gas-tight personnel access:

Fixed-Roof Petroleum Storage Tanks Atmospheric tanks storing crude oil, refined products, or intermediates where API 2000 fire-case venting calculations require emergency relief capacity beyond the conservation vent.
Chemical and Petrochemical Storage Tanks storing flammable or combustible chemicals where NFPA 30 and local fire codes mandate emergency venting and safe interior access for cleaning and inspection.
Terminals and Tank Farms Multi-tank facilities where each tank requires both emergency overpressure protection and routine interior access for API 653 inspections without removing the tank from service.
Tanks Requiring Emissions-Controlled Access Any storage vessel where maintenance access must be achieved without releasing vapors to atmosphere, requiring gas-tight manhole closures rather than open manhole covers.
Fire-Exposed Storage in Congested Facilities Tanks within dike walls or close-proximity installations where fire impingement scenarios require validated emergency vent sizing per API 2000 Annex A or NFPA 30 Table 23.6.2.

Why Shand & Jurs Emergency Vents & Manway Covers Excel

Tanks Requiring Validated Fire-Case Relief Capacity

Emergency vents are sized and tested to deliver the full vapor discharge rate required by API 2000 fire-case calculations, providing documented relief capacity that satisfies regulatory and insurance requirements.

Facilities Where Fugitive Emissions Must Be Minimized

The Expanda-Seal™ manway closure provides a gas-tight seal at the tank shell opening, reducing fugitive emissions at a point where conventional bolted covers allow vapor leakage over time.

Operations Requiring Frequent Tank Entry

Manway covers with the Expanda-Seal™ mechanism open and close without special tools, reducing the time and effort required for inspection, cleaning, and maintenance access.

Tanks Subject to Both Normal Breathing and Fire-Case Events

Emergency vents are set above the conservation vent operating range, remaining sealed during normal tank breathing and opening only when internal pressure exceeds the fire-case threshold.

Corrosive or High-Humidity Service

Metallic construction with corrosion-resistant materials and sealing surfaces maintains device integrity and seating performance in environments that degrade standard carbon steel hardware.

Emergency Vents vs. Manway Covers — Selection Guide

Attribute	Emergency Vents	Manhole Covers
Primary Function	Large-volume overpressure relief during abnormal events	Gas-tight personnel access for inspection and maintenance
Operating Trigger	Internal pressure exceeds fire-case setpoint	Operator opens for scheduled tank entry
Normal-condition State	Sealed; does not open during routine breathing	Sealed; provides continuous vapor containment
Sizing Basis	API 2000 fire-case venting calculations	Standard personnel access requirements per vessel type
Regulatory Driver	API 2000, NFPA 30, EPA 40 CFR 60/63	API 653 inspection access, OSHA confined space entry
Sealing Technology	Weighted pallet reseats after pressure event	Expanda-Seal™ gas-tight closure (bolted or quick-open)
Recommendation	Specify for every fixed-roof tank requiring fire-case overpressure protection beyond the conservation vent	Specify when the tank requires routine interior access with vapor containment at the opening

What to Consider Alongside Emergency Vents & Manway Covers

Normal-operation Tank Breathing You need pressure and vacuum relief for routine thermal breathing and pumping operations rather than fire-case events. See Conservation Vents & Seals.
Flame Protection at Tank Openings You need to prevent external flame ingress through tank nozzles or vent outlets. See Flame & Detonation Arresters.
Biogas Digester Cover Protection You need emergency overpressure relief and personnel access at an anaerobic digester cover rather than an above-ground storage tank. See Biogas Cover Equipment.
Complete Tank Breathing and Fire-case Protection Pair emergency vents with conservation vents to provide both normal-operation emissions control and fire-case overpressure relief on the same tank, meeting API 2000 requirements for both conditions. See Conservation Vents & Seals.
Overfill Prevention and Inventory Monitoring Combine with L&J Technologies level alarm probes and Varec FuelsManager® to create a layered tank protection system where overfill alarms trigger operator intervention before emergency relief is needed. See Clairvoyance.