Any industry that uses flammable liquids in bulk storage tanks will be familiar with the many safety measures required for storing, processing, and transporting them.
Leaks, fires and explosions caused by hazardous liquids and gases can be harmful to employees, contractors and even the public.
One of the many safety devices found in bulk liquid storage is a flame arrester.
How do flame arresters work?
Flame arresters are passive safety devices attached to storage tank vents, pipelines and processing equipment. There are two main types, deflagration and detonation arresters.
On tanks, deflagration arresters function by preventing ignition of the liquid or gas inside by protecting it from sparks. They extinguish flames and sparks by absorbing the heat using a heat sink mechanism such as a ceramic matrix or metal ribbon.
In stopping a flame front before it accelerates beyond subsonic speeds, a fire cannot propagate and cause an explosion.
Detonation arresters work similarly, but for explosions. An explosion is simply a faster fire, moving at supersonic speed, where the pressure is high enough for the gas to auto-ignite.
At the same time, both devices can allow gases to escape the vessel or move along the pipeline, preventing build-up and overpressurisation.
If a flame arrester fails to work correctly, it can have devastating consequences to human lives and to the business.
Where are flame arresters required?
Arresters are needed in any environment where flammable liquids and gases are stored or where escaped fumes could mix with air to create a flammable mixture.
Installation of flame arresters comes under the Health & Safety Executive (HSE) guidance for Dangerous Substances and Explosive Atmospheres Regulations 2002.
The approved code of practice recommends ways of reducing the risk of explosions through the design of plants, storage of substances and ways for risk to be controlled.
These can be gas or flammable liquid processing systems, incinerators, waste gas venting and vapour recovery systems. Another factor influencing the use of an arrester is the high risk of potential ignition sources.
They should be placed at or near atmospheric vents rather than used in pressurised systems.
How often should flame arresters be inspected?
Ideally, every plant and storage facility should conduct regular checks for corrosion and damage to equipment. Safe cleaning, maintenance and repair of equipment falls under the HSE’s approved code of practice for dangerous substances.
As with any safety equipment, it is best practice to follow the manufacturer’s recommendations for inspections.
As a general rule, inspect arresters a minimum of once a year and ideally every three months. If areas are at a particularly high risk of a flame event or if the equipment is heavily used, inspect them as often as once a month.
This will allow you to replace units if the damage is substantial before an accident happens.
When inspecting, look for obvious external damage, for example, corrosion and damage to the casing. Check for changes in colouring, cracks, and dirt deposits in joins.
If the unit is easily accessed then check for debris and blockages, holes in the matrix material, and any warping to the internal structure.
If a flame event occurs, conduct an inspection when it is safe to do so and replace the unit.
How should flame arresters be cleaned?
Regularly cleaning flame arresters will enable them to function more efficiently if there is a flame event, and it will increase the lifespan of the equipment.
Recommended schedules for cleaning will depend on usage and the type of conditions on site, but usually every three to six months.
Cleaning will require the process to be stopped completely before work begins, and any open valves should be closed. Appropriate levels of PPE will be required for the staff undertaking the cleaning.
Inspect the arrester before cleaning it. Cleaning methods can include using non-flammable solvents, compressed air, pressurised steam or a soft brush.
Hard-bristle brushes and edged tools are not usually recommended and can cause damage. However, it is always best to check the manufacturer’s advice on how and when to clean the arresters.
When should you replace flame arresters?
The average lifespan of a flame arrester used on a storage tank is five years. However, the figure is only an estimate and does not take into account heavy usage and any corrosion or damage from the environment on-site.
In harsher environments, the lifespan will be understandably shorter. In contrast, using a flame arrester made from high-quality, robust materials will increase its longevity.
In the event of any fire or explosion where the arrester is activated, the device should be replaced as soon as possible.
Safe storage and processing of petrochemical substances come with risks of fire events. However, the proper installation, cleaning, inspection and maintenance of flame arresters can make a processing site safer for everyone.
