Chemical Decontamination: Degassing and Vapour Suppression Chemical FAQ

Are you struggling to reduce LEL readings in tanks and vessels during shutdown and turnaround cleaning?

Do you need to speed up chemical decontamination and degassing procedures so your crew can safely enter vessels for inspection?

Or maybe you need to drop LEL levels in your tanker so you can safely dispose of oil field wastewater. 

In this guide, we cover common questions about chemical decontamination, including degassing or vapour phase cleaning and decontamination, as well as vapour suppression. We’ll also explore what an LEL Scavenger is, how they work, why you need them, their benefits, and costs. 

You’ll learn how Degassing Chemicals and LEL Scavengers help you speed up your shutdown & turnaround operations, improve safety and reduce cleaning and degassing times. Best of all, armed with this knowledge, you’ll be able to speed up vessel entry time for cleaning and inspection—and reduce your overall downtime. 

Table of Contents

What is Degassing?

In oil & gas processing and production, degassing commonly refers to the process of removing hazardous vapours or gases from processing vessels, tanks, and piping. These hazardous vapours are often released by hydrocarbon and waste fluids being stored or transported and accumulate in the headspace. These vapours are often referred to as VOCs or LELs.

Learn more about degassing in shutdown & turnaround operations.

What is LEL?

LEL, or “Lower Explosive Limit,” refers to the minimum concentration a specific gas can ignite or combust. It’s the lowest concentration of gas needed to cause a fire or explosion when exposed to a source of ignition such as a spark or flame. If the gas concentration falls below this limit, there’s not enough of it to trigger an ignition. Many gas monitors can measure LEL concentrations, that’s why the gases in these tanks and process vessels are often referred to as LELs. 

What are LEL Scavengers and What is LEL Scavenging?

LEL scavengers are degassing chemicals used to reduce the concentration of volatile organic compounds (VOCs) and their LEL levels. They are used for “chemical decontamination” and reduce hydrocarbon vapours and BTEX (benzene, toluene, ethylbenzene, and xylene) gases in tanks, vessels, process piping, and other equipment. 

LEL scavenging is the process of applying LEL Scavengers to reduce lower explosive limit (LEL) levels. 

How Do Degassing Chemicals like LEL Scavengers Work?

LEL scavengers are specially formulated multi-functional degassing chemicals that reduce VOCs or LEL levels. They are surfactant-based and function by emulsifying hazardous hydrocarbon gases. Some LEL scavengers like Purge HF also scavenge and remove H2S. 

LEL scavengers don’t directly draw hazardous gases out of the headspace but rely on contact to emulsify them. This means if they are sprayed, or applied via steaming or steam purge they draw the hazardous gases out of the gas phase and bring them into the liquid. 

LEL scavengers can also act to suppress hydrocarbon vapours when sprayed on, or blended into the liquid within the tank. Again, the primary function is through emulsification or encapsulation where the LEL scavenger surrounds the hydrocarbon molecule binding it in the liquid phase. 


Why Use LEL Scavengers and Vapour-Phase Decontamination Chemicals?

Safety and Efficiency

LEL scavengers are vapour-phase decontamination chemicals used to remove unwanted gases, reduce risk of explosion and fire, improve handling and disposal safety—and create a safer environment within the tank or vessel. 

The surfactants in most LEL Scavengers also clean or decontaminate tanks, vessels, piping, and petroleum process & production equipment. They increase cleaning efficiency, improve safety, and reduce the need for manual cleaning. If vessel entry is required, LEL Scavengers reduce the time before the vessel can be safely entered. 

What Types of LEL Scavengers Are Out There?

Several types of LEL Scavengers are available. Most are water-based and don’t contribute to LEL or volatile organic compound (VOC) levels in your process. Your chemical supplier will work with you to determine the right LEL Scavenger for your application.

How Regularly Should Vapour-Phase Cleaning be Done?

The answer depends on your equipment, its application, and the hydrocarbon gas or (VOC) levels. LEL scavenging should be included in: 

How Does Vapour-Phase Cleaning and LEL Scavenging Compare to Other Methods of Hydrocarbon Removal?

Vapour-phase cleaning and LEL scavenging are safe, effective, and efficient methods for removing hydrocarbon vapours. In applications where high levels of LELs may be present, LEL scavengers reduce the risk of explosion, fire, and exposure. Vacuum extraction, sparging, and thermal oxidation are less common but sometimes used to reduce LEL levels. 

Other methods, such as vacuum trucks or skimmers are often limited to removing liquid waste and do nothing to reduce LELs and hydrocarbon vapours. LEL scavenging can be used with other methods (Nitrogen) to achieve the complete removal of hydrocarbon (VOC) liquids and vapours from your process or tank. 

Do LEL Scavengers also act as Vapour Suppression Agents?

Yes, LEL scavengers can prevent or suppress the release of hydrocarbon vapours from waste fluids. They can be applied on the surface either by spray or foam for vapour suppression applications. In these applications, LEL scavengers are only effective on fluids with a high-water content. They cannot be used to prevent the release of hydrocarbon vapours from fluids with high hydrocarbon content. 

How Can We Gauge LEL Scavenging Effectiveness?

To gauge the effectiveness of your LEL Scavenging, Vapour Suppression, or Vapour-Phase Cleaning process, measure LEL levels before and after scavenging. LEL levels are commonly tested using portable and process LEL monitors.

Where are LEL Scavengers and Vapour-Phase Cleaners Most Commonly Used?

The most common applications for LEL scavenging include chemical decontamination and cleaning of tanks, vessels, and equipment used to store or transport hydrocarbons, such as crude oil, gasoline, and diesel fuel. It is also common to add LEL scavengers of vapour-phase cleaners when hauling waste oil field fluids for disposal.

LEL scavenging or vapour-phase decontamination is common in oil and gas, petrochemical, and chemical industries.

What is the typical dosage for LEL Scavengers and Vapour-Phase Cleaners?

Dosage is dependent on application, but 1-3% based on the volume of fluid in the tank is commonplace. They are often applied via high pressure, gamma jet, steam purge, cascade, flood or foam. 

How Much do LEL Scavengers Cost?

LEL scavenging costs vary by application and concentration of hydrocarbon or LEL vapours. Depending on application, you may spend a few hundred dollars for a pail or two, or several thousand dollars for larger volumes such as totes or bulk delivery of LEL Scavengers. 

While cost may be a concern, the costs of not using LEL Scavengers are often far greater. Reducing LEL levels improves safety, reduces downtime and reduces fluid disposal costs. Fluids releasing high levels of LELs are often more costly and require specialized facilities for disposal due to their hazardous nature. 

Overall, LEL scavenging costs are a small fraction of the cost of your shutdown and turnaround operation. LEL scavengers reduce the cost of these operations by: 

  • Reducing cleaning time 
  • Reducing time to vessel entry 
  • Reducing the need for manual cleaning 
  • Reducing equipment, process, and vessel downtime 

Are LEL Scavengers Compatible with other Chemicals?

Absolutely! LEL Scavengers are often combined with Iron Sulfide Scavengers, H2S Scavengers, and other industrial cleaning chemicals. If Guardian Chemicals is your supplier, we will recommend the right chemical combination and concentration for your unique application.


LEL scavenging and vapour-phase cleaning are more than just a process—they’re a safety net.

LEL scavengers remove hazardous hydrocarbon gases from your systems and processes. LEL scavengers are cost-effective chemical solutions to reduce LEL concentrations and ensure efficient tank, vessel, and process cleaning operations. They’re often used in shutdown and turnaround operations to speed up operations, reduce manual cleaning, and reduce time for vessel entry. 

Now that you know all about LEL Scavengers, what’s the next step? When you’re ready, contact us to see how you Create a Better Future with our custom tank, vessel and process cleaning chemical solutions. And if you’ve got a shutdown and turnaround coming up, see how our LEL, H2S, and Iron Sulfide Scavengers can help you enhance safety and reduce downtime. 

Together with Chemistry Done Better we can reduce the risk of fire and explosion in your cleaning operations—and help create a safer environment for your workers. 

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