How Emergency Vents Prevent Catastrophic Tank Failures

In industrial sites which have flammable, volatile, or hazardous materials stored in tanks or vessels, safety becomes a paramount concern. One important safety component in these systems is the more widely accepted secondary device known as the emergency vent. The emergency vent was developed to provide instantaneous overpressure relief in the case of an emergency circumstance. Emergency vents are an essential part of any pressure management plan.

In this paper we will examine what emergency vents are, the principle behind their operation and their importance in the protection of people, property and facilities.

What are Emergency Vents?

Emergency vents are secondary relief devices, which provide overpressure protection for tanks and are intended to avoid excessive internal pressure, and potentially catastrophic scenarios, caused by sudden energy events - for example, exposure to intense heat as when a tank is involved in a fire, along with a range of other scenarios when internal pressures exceed extreme rupture limits.

As secondary relief devices - emergency vents operate under different pressures than normal pressure relief / vacuum valves (prv's and vlv's) and are not intended to replace them. Emergency where designed to open only under different conditions of excessive pressures, which allow the safety of the tank and its structural integrity is acknowledged.

Their purpose is to prevent a tank rupture, explosion, or escape of hazardous material when normal venting systems are subjected to excessive vapour and/or disturbed or inoperable.

What are Emergency Vents and how do they work?.

When a storage tank is temperatures exposed to extreme heat, or pressurized materials - as when large amounts of heat are generated or transferred from external sources like extremely large mass or flames, or by rapid establishment of high pressure (thermal expansion) - the pressure can accelerate above design limits. Emergency vents will quickly open at a predetermined pressure, to allow vapour or gas to vent.

Normal activation scenarios for emergency vents are:

Fire engulfing tanks

Blocked vent lines or filters

Power failure to mechanical pressure control systems

An unanticipated and/or exothermic reaction of tank contents

Emergency vents are a critical last line of defense because they activate fast and automatically.

Types of Emergency Vents

There are many emergency vent types, and manufacturers adopted them into industrial applications including:

Spring Loaded Vents

Open at a set pressure point utilizing a calibrated spring.

Weighted Pallet Vents

Open when the weight is lifted utilizing gravity and specific pressure.

Combination Pressure/Vacuum/Emergency Vents

Provides venting in the standard operation mode, and vents in the emergency situation.

Flame Arrested Emergency Vents

Provide emergency relief from pressure but prevent flame from propagating into the tank.

Selection of which type of emergency vent to use is made based on tank design, contents, and environmental risks.

Applications for Emergency Vents

Emergency vents are utilized in many industries that are considered to be high risk including:

Petroleum storage tanks

Chemical manufacturing facilities

Food and beverage processing

Pharmaceutical manufacturing

Agricultural silos and fertiliser tanks

Water and wastewater treatment facilities

An accounting of any process that uses volatile liquids or gases will benefit from having emergency vent protection.

Benefits of Emergency Vents

There are many safety and compliance advantages to emergency vents including:

Immediate action to extreme overpressure

Protection from tank failure or explosion

Reduction of environmental discharge of hazardous materials

Low maintenance and easy to inspect

Assists with safety and environmental compliance

Choosing An Emergency Vent

Choosing the right emergency vent will require considering multiple factors. Examples include:

Venting Capacity - It will need to be calculated based on the size of the tank and fire-case scenarios

Operating Environment - What is the temperature range and should the area be worry about, indoors or outdoors

Material Compatibility - Do we want stainless steel, aluminum or corrosion-proof materials

Substance Stored - Are we storing flammable, corrosive, or cryogenic materials

Industry Standards - Do we need to comply with any API 2000, OSHA, NFPA, and ISO regulations

Optional features - Should we be looking at the vent option of flame arresters, weather hoods or gas-tight sealing

You should always check with an engineer or supplier to insure you have the right size and certification!

Installing and keeping vents in good shape

Maintain vent performance by:

Select the highest point on the tank

Ensure path is unobstructed

Look for corrosion or wear, stuck mechanisms

Replace gaskets and seals as needed

Perform regular pressure tests per your safety program

Wrapping it up

Emergency vents are a critical safety device for industrial tanks and vessels. By allowing immediate pressure relief in the event of a fire or any type of failure, it protects valuable assets, reduces downtime, and most importantly, protects human life. If you are the responsible party of any type of hazardous storage system, please ensure that your emergency venting solutions are properly specified, designed, installed and maintained. Always consult with your industry representative and adhere to current compliance standards.