Combustible Dust Testing

Laboratory testing to quantify dust explosion and reactivity hazards

Safety Data Sheets

Develop critical safety data for inclusion in SDS documents

Gas and Vapor

Laboratory testing to quantify explosion hazards for vapor and gas mixtures

Classification of hazardous materials subject to shipping and storage regulations
Testing and consulting on the explosion risks associated with devices and processes which use or produce hydrogen
Safety Data Sheets

Develop critical safety data for inclusion in SDS documents

Thermal Stability

Safe storage or processing requires an understanding of the possible hazards associated with sensitivity to variations in temperature

Adiabatic Calorimetry
Data demonstrate the consequences of process upsets, such as failed equipment or improper procedures, and guide mitigation strategies including Emergency Relief System (ERS) design
Reaction Calorimetry
Data yield heat and gas removal requirements to control the desired process chemistry
Battery Safety

Testing to support safe design of batteries and electrical power backup facilities particularly to satisfy UL9540a ed.4

Safety Data Sheets

Develop critical safety data for inclusion in SDS documents

Cable Testing
Evaluate electrical cables to demonstrate reliability and identify defects or degradation
Equipment Qualification (EQ)
Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions
Water Hammer
Analysis and testing to identify and prevent unwanted hydraulic pressure transients in process piping
Acoustic Vibration
Identify and eliminate potential sources of unwanted vibration in piping and structural systems
Gas & Air Intrusion
Analysis and testing to identify and prevent intrusion of gas or air in piping systems
ISO/IEC 17025:2017

Fauske & Associates fulfills the requirements of ISO/IEC 17025:2017 in the field of Testing

ISO 9001:2015
Fauske & Associates fulfills the requirements of ISO 9001:2015
Dust Hazards Analysis
Evaluate your process to identify combustible dust hazards and perform dust explosion testing
On-Site Risk Management
On-site safety studies can help identify explosibility and chemical reaction hazards so that appropriate testing, simulations, or calculations are identified to support safe scale up
DIERS Methodology
Design emergency pressure relief systems to mitigate the consequences of unwanted chemical reactivity and account for two-phase flow using the right tools and methods
Deflagrations (Dust/Vapor/Gas)

Properly size pressure relief vents to protect your processes from dust, vapor, and gas explosions

Effluent Handling

Pressure relief sizing is just the first step and it is critical to safely handle the effluent discharge from an overpressure event

FATE™ & Facility Modeling

FATE (Facility Flow, Aerosol, Thermal, and Explosion) is a flexible, fast-running code developed and maintained by Fauske and Associates under an ASME NQA-1 compliant QA program.

Mechanical, Piping, and Electrical
Engineering and testing to support safe plant operations and develop solutions to problems in heat transfer, fluid, flow, and electric power systems
Hydrogen Safety
Testing and consulting on the explosion risks associated with devices and processes which use or produce hydrogen
Thermal Hydraulics
Testing and analysis to ensure that critical equipment will operate under adverse environmental conditions
Nuclear Safety
Our Nuclear Services Group is recognized for comprehensive evaluations to help commercial nuclear power plants operate efficiently and stay compliant
Radioactive Waste
Safety analysis to underpin decomissioning process at facilities which have produced or used radioactive nuclear materials
Adiabatic Safety Calorimeters (ARSST and VSP2)

Low thermal inertial adiabatic calorimeters specially designed to provide directly scalable data that are critical to safe process design

Other Lab Equipment and Parts for the DSC/ARC/ARSST/VSP2 Calorimeters

Products and equipment for the process safety or process development laboratory


Software for emergency relief system design to ensure safe processing of reactive chemicals, including consideration of two-phase flow and runaway chemical reactions


Facility modeling software mechanistically tracks transport of heat, gasses, vapors, and aerosols for safety analysis of multi-room facilities


Our highly experienced team keeps you up-to-date on the latest process safety developments.

Process Safety Newsletter

Stay informed with our quarterly Process Safety Newsletters sharing topical articles and practical advice.


With over 40 years of industry expertise, we have a wealth of process safety knowledge to share.

Recent Posts

Determining Limits of Flammability: Which ASTM Method E918 vs. E681?

Posted by Fauske & Associates on 08.12.19

TJ Frawley, Project Manager, Flammability Testing and Consulting Services, Fauske & Associates, LLC

When determining the flammability limits of your product for an SDS or to optimize your process while maintaining high safety standards, it can be somewhat confusing choosing the correct testing method. The two most requested methods are ASTM E918: Determining Limits of Flammability of Chemicals at Elevated Temperature and Pressure and ASTM E681: Concentration Limits of Flammability of Chemicals (Vapors and Gases).

This piece will examine the differences between these two types of flammability tests and the advantages and obstacles of those differences. As a starting point, the most glaring difference between the two is that E918 is performed in a 5-Liter stainless steel vessel and E681 is performed in a 5-Liter glass flask that incorporates a rubber stopper to seal the vessel. It is important to remember this key difference as it is the basis which most greatly sets the two methods apart and can thus influence data interpretation.

The similarity of the methods are few but deserve mention. Both methods aim to determine the same outcome – boundaries of vapor/gas flammability. Both can be run at elevated temperatures, although E918 allows for a greater range; and E918 can also be run at above, or below, atmospheric pressures.

It is the opinion of the Flammability division here at Fauske and Associates that E918 is the better of the methods because of the increased accuracy, versatility, and safety, that testing in a stainless steel vessel can provide.

ASTM E918 has a greater accuracy because the resolution of an ignition is determined by an established percentage of pressure increase which is measured by calibrated pressure transducers. In the United States a 7.0% rise of absolute pressure constitutes an ignition. At the ambient pressure of 14.7 psia, the 7.0% rise is equal to an increase of 1 psia in pressure. Europeans use a 5.0% pressure rise criterion as the defining threshold of an ignition as is stated by the Swedish Standards Institute in SS-EN 1839.

Below is a chart displaying a dataset of five tests determining the LFL of methane. The yellow highlighted cells illustrate a 5.11% pressure rise (Test #5). This would be considered an ignition in Europe, and the LFL of methane would be reported as 4.7% fuel (assuming testing of 4.6% resulted in non-ignitions). However, in the United States, Test #2 where a pressure rise of 7.56% occurred, would be considered an ignition, and 4.8% fuel would be reported as the LFL (blue highlighted cell).

5 datasets of lfl flammability tests

The conception the 7.0% pressure rise and 5.0% pressure rise are not without controversy. The reasoning for those numbers being used as an ignition threshold are still debated today. However, there is consistency for every lab in the United States using a 7.0% pressure rise, and there is consistency across European labs that use a 5.0% ignition indicator. The end user of the LFL data needs to be aware of the exact method used for the determination.

While E918 has an objective, clear, and distinct definition of an ignition, E681 relies on subjective visual observations to make the distinction between an ignition and a non-ignition. The standard states in section 3.1.2, “propagation of flame – as used in this test method, [is] the upward and outward movement of the flame front from the ignition source to the vessel walls or at least to within 13 mm of the wall, which is determined by visual observation.” This creates bias when determining “what is and what isn’t an ignition.” What one person may interpret as an ignition, another person may disagree. Herein lies the uncertainty in the end results.

Below are two charts comparing the LFL results of methane obtained being using each standard. The top chart has data from ASTM E918, and the bottom chart was obtained from ASTM E681. Please note the difference of fuel percentage that correspond with the lowest ignition. Using ASTM E918 the reported LFL is 4.83%. The result using ASTM E681 in the glass flask is about 0.2% higher.

Lower Flammable Limit of Methane in a 5-L Stainless Steel Vessel

lower flammable limits of methane in steel vessel

Lower Flammable Limit of Methane in a 5-L Glass Vessel

lower flammable limits of methane in glass vessel

Correlation does not equal causation, therefore, the difference in results may not stem from the differences in the standards. However, based on the data in the top chart using a 7.0% rise as the threshold for an ignition, we can clearly distinguish an ignition from a non-ignition. The lower chart is more ambiguous.

Even when using video to record testing of E681, the outcome is not always as dependable in practice as the standard describes.

In this picture our ignition source is fired. It
appears that a flame is in the beginning
stages of propagating.








Here a flame has been identified. However, it
must propagate upward and outward to be
considered an ignition.


beginning stages of flame propogation

The pictures above depict a typical test ran according to ASTM E681. While this test is more visually appealing than watching a line move on a graph, it can be difficult to view and interpret. These pictures were specifically chosen to illustrate the difficulty of determining an ignition visually. This is not an uncommon scenario.

Any material that may produce a residue or a solid product in decomposition, such as chemicals with a saline group or one that generates soot or tar, will decrease the technician’s visibility and impair their ability to distinguish between an ignition and a non-ignition.

E918 also has more versatility and can replicate more processes by being able to reach higher pressures and temperatures. Here at Fauske and Associates using E918 we have been able to perform testing above 300 psia. The other method cannot test at any pressures above ambient levels. According to E681, the 5-L glass flask is vacuum sealed with a rubber stopper.

a diagram of E681 setup with a rubber stopper sealing the glass flask

a stainless steel 5-L vessel sealed with a stainless steel lidOn the top: a diagram of E681 setup with a rubber stopper sealing the glass flask
On the bottom: a stainless steel 5-L vessel sealed with a stainless steel lid

If pressurized above ambient pressure, the rubber stopper will pop, and the test mixture will be compromised. Not only will this test have to be repeated, if the sample is hazardous, a safety concern now exists.

Finally from a safety perspective, testing in a completely sealed stainless steel vessel is overwhelmingly preferable to testing in a glass flask that relies on a vacuum sealed rubber stopper.

Stainless steel will not crack or shatter; glass might. Although engineers and technicians are trained and experienced at avoiding dangerous scenarios, the possibly remains. We are igniting chemicals that may result in high pressure explosions. It is not outside the realm of possibly for the glass flask to crack or break.

As previously mentioned, a steel vessel can be pressurized. This is also very important for purging the vessel after a test. Any hazardous decomposition products can be purged by pressurizing the vessel with nitrogen and then evacuated into a scrubbing system or into a fume hood. This cannot be done in a glass flask. As soon as the pressure inside the flask becomes
greater than the atmosphere outside the flask, the rubber stopper will break its seal with the glass flask and hazardous gases or vapors will be ejected from the flask in an uncontrolled manner into the surrounding environment. Therefore, the purging process must rely on vacuum purging alone, which most likely will increase the time to fully purge. This adds to the total
turnaround time of the test and an increase in cost.

There are benefits to E681. It is visually more appealing because a person can actually see reactions in the vessel. Also the equipment for E681 is less expensive and may be less expensive to perform testing.

It is always important to know the pros and cons when choosing a testing standard. For more information on flammability testing go to our flammability testing page which contains information on FAI's testing methods along with other flammability testing resources. 

Explore FAI's Flammability Testing Services & Resources


Topics: Flammability, Reactive Chemicals, Testing


Is My Dust Combustible?

A Flowchart To Help You Decide
Download Now