Safety in industrial environments is not optional, it’s paramount. One of the most important elements found in the protection of storage tanks – especially for facilitating the storage of volatile or hazardous materials, is the emergency vent.
The emergency vent is able to restrict the dangerous collapse of a tank because of surging pressure event or a vacuum condition. Placement and protection of the environment, compliance with regulations and improved safety in the workplace all depend on the emergency vent. If you are responsible for chemical storage tank or process tank operations, understanding how emergency vents function, and selecting the right emergency vent, is critical.
What is an Emergency Vent?
An emergency vent is a safety accessory – for the tank – which automatically opens to relieve excess internal pressure (or vacuum). Accessibility to relieve an emergency sector of the internals of the tank is achieved by external vapour venting caused by an abnormal operating condition including but not limited to:
Fire
Rapid temperature change
Overfilling
Flash vapourisation
Equipment failure
By quickly relieving the pressure from the tank, the danger of explosions, loss of the tank due to rupture, and product loss will be avoided – ultimately protecting people and assets.
Where Are Emergency Vents Used?
Emergency vents are normally used on atmospheric pressure, low pressure (100kPa) tanks – used for the storage of:
Petrochemical storage facilities
Chemical production plants
Food and beverage manufacturing
Pharmaceutical and biotech industries
Liquid agricultural storage
Whenever there is the storage of flammable, corrosive, or sensitive liquids, emergency vents must be regarded as an additional level of protection.
How Do Emergency Vents Work?
Emergency vents are pressure-actuated devices. If the internal pressure is above a certain safe level, the vent will open auto ho-matically, allowing for vapor or gas to escape. Once the internal pressure is de-escalated back to a normal safe level the vent will automatically reseal itself.
Most emergency vents include:
• spring or weight-loaded actuating devices
• gaskets and seals for gas-tight sealing
• self-attaching hoods to provide protection against contamination, and product loss from the vent outlet.
Emergency venting is generally used along with pressure/vacuum relief valves, and flame arrestors for tank protection.
Emergency Vent Types
Emergency vents come in numerous varieties. Each design is indicative of the different needs of the specific industrial applications.
• Spring Loaded Vents automatically vent at a dead weight (open) pressure. It may be used for a standard storage tank with pressures of up.
• Manhole / Hatch Style Vents offer online venting as well as access to the tank internal for inspection, cleaning, etc. This helps to provide benefits of pressure relief and ventilation in controlled tank access.
• Combination pressure/vacuum vents afford the user pressure relief from a build-up of pressure and venting for vacuum collapse. These valves have been used in combination with sealed storage in agricultural, manufacturing, and retail warehouses.
• Vents with flame arrestor are used in operational facilities which manufacture process or work in a flammable atmosphere. A flame arrestor will permit venting of gas but prevent propagation of flame as gas is vented into the atmosphere.
Choosing the Correct Emergency Vent
When selecting the proper emergency vent, you will want to consider many factors, including:
Size and Volume of the tank
Material to be stored (flammable, corrosive, volatile)
Required venting capacity (SCFH or m³/hr usually but could be FT³/hr)
Operating pressure and vacuum settings
Material compatibility (e.g., corrosive media requires stainless steel)
Consult a technical source or the API 2000 standard for proper vent sizing and selection.
Safety & Compliance Standards
In order to ensure safe, as well as legal compliance, emergency vents should comply with:
API 2000 – Venting Atmospheric and Low-Pressure Storage Tanks
OSHA – Workplace safety
NFPA – Fire prevention
EPA – Environmental compliance (especially in Australia)
When purchasing venting equipment, always select a certified product from a reputable manufacturer that has documented test results.
Installation & maintenance advice
Proper installation and maintenance will ensure that your emergency vents operate as specified:
Install the vents at the highest point of the storage tank to ensure the best efficiency.
Use chemical-resistant gaskets, with corrosion-resistant materials.
Plan for frequent inspections for corrosion, the integrity of seals, and the proper actuation of venting.
Ensure that vent openings are kept free from any debris or obstructions.
Check the relief pressure settings each year.
Common Emergency Vent Problems
Look for the warning signs below:
Vents that stick or leak.
Vents that are not resealing after the venting process.
Opening that are blocked due to corrosion or debris.
Improper application or sizing.
These conditions can affect safety, with damage to the tank and costly environmental spills if not addressed.
Conclusions
An emergency vent is a major component of a tank safety system when you are keeping flammable liquids there, and when you are keeping chemicals, or even something as food grade. They should be carefully selected, installed, maintained and run to a safety specification, by so doing, they can also lessen the chances of a pressure event or disaster and at the same time, they may be run to a safety specification.
