Flammability Testing

Chilworth provides flammability testing as part of our process safety services and laboratory testing services.

It is a function of a Process Hazard Analysis (PHA) to identify those inherent properties, conditions or equipment that could cause injury to personnel, the environment, or facilities. Gases and vapors have one property that can make them particularly problematic. They readily mix with air. This means that loss of containment incidents can quickly expose processes and personnel to fire or explosion hazards if the gas or vapor is combustible, the results can be catastrophic.

What properties are of most concern? Because gases and vapors can quickly mix with air, short-term effects, or acute properties are of greatest safety interest. The ability of gases and vapors to form ignitable mixtures with air or other oxidants can lead to several hazardous conditions including flash fires, pool fires, jet fires, vapor cloud explosions and detonations. As the concentration of a released gas or vapor increases a point is reached when a flame can propagate away from an ignition source. This concentration is called the Lower Flammable Limit (LFL) for the material. This concentration varies with system pressure and temperature and may need to be measured under other than standard conditions. If the concentration of the gas or vapor continues to increase it will ultimately reach a point at which there is insufficient amount of oxidant to allow flame propagation. This concentration is called the Upper Flammable Limit (UFL) and forms the upper end of the flammable range.

If ignition of a gas/air or vapor/air cloud occurs rapid burning is initiated and several possible outcomes are possible. If the cloud is unconfined, a flash fire will be the result. The high temperature flame and combustion products pose a danger to personnel and facilities. If the flash fire is confined, or if conditions are right for flame acceleration, then a vapor cloud explosion (VCE) will occur. A VCE can cause extensive facility and equipment damages and threaten personnel over a wide area. The vapors from a flammable liquid can flash back and ignite the liquid pool resulting in dangerous radiation levels and spreading the fire. Flammable liquid fires are difficult to extinguish.

The release of gases or vapors under pressure can cause jet fires. These fires are fuel rich and burn very hot. Besides the obvious hazard associated with the torch, jet flames pose an extreme hazard to nearby storage tanks. If the storage tank is pressurized and contains a super-heated liquid, such as a propane tank, and the flame “impinges” on the unprotected shell a catastrophic stress failure is likely. Such a failure can lead to a Boiling Liquid Expanding Vapor Explosion, or BLEVE. The effects of a BLEVE include missiles, blast and if the contained material is combustible, a fireball with extreme radiation hazard. The contained material does not have to be flammable for a BLEVE to occur. It is the pressure and rapid phase change that causes the physical damage. Materials such as chlorine and anhydrous hydrogen chloride can BLEVE.

If you store or process flammable gases or liquids and need to access your fire and explosion risks, Chilworth Global has experienced Process Safety Engineers who can help. The Chilworth Global Lab can provide you with all of the critical flammable property data needed to assess risk at both ambient and process conditions.

Minimum Ignition Energy Test – Vapor
The minimum ignition energy (MIE) test determines the lowest spark energy capable of igniting a sample under the test conditions. The test is used primarily to assess the potential vulnerability of vapors to electrostatic discharges, but is also relevant to frictional sparks.

Chilworth determines the MIE of a vapor using an ignition chamber mounted above a sample reservoir which is submerged in a temperature controlled bath. Vapors evolve into the ignition chamber either naturally or by application of a slight negative pressure. Attempts are made to ignite the vapor with discrete capacitive sparks of known energy. Trials are repeated over an appropriate range of sample temperatures.

Limits of Flammability
Under various conditions of temperature and pressure, liquids will evolve a certain quantity of vapor. For pure substances, the concentration of this vapor can be easily determined using the vapor pressure of the substance and the system pressure. For some substances, the vapor evolved may be flammable over a certain range of concentrations defined by the upper and lower flammable limits — the UFL and LFL respectively.

The UFL and LFL define the range of flammable concentrations for a substance in air at atmospheric pressure. The limits of flammability may be used to specify operating, storage, and materials handling procedures for a material. They are particularly useful in specifying ventilation requirements for operations involving flammable liquids and gases.

Chilworth determines limits of flammability in accordance with American Society for Testing and Materials (ASTM) Method E681-94. The method involves creating a uniform mixture of the sample vapor with air in a closed vessel and attempting to ignite the mixture using an energetic spark ignition source. Trials are repeated for various concentrations of the sample vapor in air until the concentration that will just sustain flame propagation is determined.

Vapor Pressure
The vapor pressure will be measured using the isoteniscope technique specified by ASTM 2879 – 96 or equivalent techniques.

Limiting Oxygen Concentration Test
The Limiting Oxygen Concentration (LOC) determines the minimum concentration of oxygen capable of supporting combustion. The LOC test is used to study explosion prevention or severity reduction involving the use of inert gases and to set oxygen concentration alarms or interlocks in inerted plant and vessels.

LOC test at atmospheric pressure is performed in a 5 liter glass flask. Various concentrations of the gas or vapor in air are prepared in the vessel and attempts are made to ignite the flammable atmosphere using a continuous electric arc ignition source. Trials are repeated for decreasing oxygen concentrations until the LOC is determined.

Flash Point Determination
The flash point of a liquid is the lowest temperature at which sufficient vapor is evolved to form a flammable mixture in air at standard atmospheric pressure. The flash point provides a simple, convenient index for assessing the flammability of a wide variety of materials.

Chilworth generally measures flash points in accordance with American Society for Testing and Materials (ASTM) Method D93-94 using the Pensky-Martens Closed Cup apparatus. Closed cup testers prevent the loss of low boiling components by keeping the sample enclosed until the ignition source is introduced. For this reason, closed cup flash point data are more conservative than — and generally preferred to — open cup data. However, Chilworth does offer other methods of flash point determination which may better suit the particular needs of the client.

Flash Point Determination – Setaflash Closed Cup Apparatus
The flash point of a liquid is the lowest temperature at which sufficient vapor is evolved to form a flammable mixture in air at standard atmospheric pressure. The flash point provides a simple, convenient index for assessing the flammability of a wide variety of materials.

Chilworth can obtain the flash points in accordance with American Society for Testing and Materials (ASTM) Method D-3278 using the Setaflash Closed-Cup Apparatus. This test method is applicable to products having a flash point between 0 and 110°C and viscosity lower than 150 st at 25°C. Closed cup testers prevent the loss of low boiling components by keeping the sample enclosed until the ignition source is introduced. For this reason, closed cup flash point data are more conservative than – and generally preferred to – open cup data.

Autoignition Temperature Determination
The autoignition temperature (AIT) of a substance is the lowest temperature at which the material will spontaneously ignite in the absence of an external ignition source, such as a spark or flame. The autoignition temperature may be used to specify operating, storage, and materials handling procedures for a material.

Chilworth measures autoignition temperature in accordance with American Society for Testing and Materials (ASTM) Method E659. A sample of the test material is introduced into a uniformly heated flask and observed for 10 minutes or until ignition occurs. The flask temperature and sample size are varied until the AIT is identified.

Autoignition Temperature at High Pressure
The autoignition temperature (AIT) of a material is the lowest temperature at which the material will spontaneously ignite. Spontaneous ignition implies that the material ignites in the absence of an external ignition source, such as a spark or flame. The autoignition temperature may be used to specify operating, storage, and materials handling procedures for a material.

The proposed AIT tests shall be conducted based on the American Society for Testing and Materials (ASTM) Method E659. The ignition of the flammable atmosphere is detected by measuring the temperature as well as the pressure rise. Because of the high initial test pressure and limitations on the design strength of the reactor, AIT greater than 300 °C will not be determined.

Explosion Severity / ( Pmax, dP/dt – Kg )
Chilworth performs explosion severity testing at high pressure using pressure using a small reactor apparatus. Liquid or solid samples are introduced to the explosion chamber. The reactor is sealed, pressurized to the test pressure, and a waiting period is observed to allow liquid samples to vaporize and the gas/vapor concentration to reach equilibrium. The mixture is then ignited by means of a fuse wire, or a constant electrical arc from a high voltage transformer. A computer is used to record the pressure vs. time characteristics of the resulting explosion. The gas or vapor concentration is varied to determine the conditions which give the maximum value for each parameter. The values for maximum pressure and maximum rate of pressure rise are determined and used to establish the explosion index (KG) for the sample. This data can then be used to design explosion protection measures and equipment. In the absence of a consensus ASTM or international standard, the Chilworth method is based on National Fire Protection Association (NFPA) Guide 68.

Open Burning Test – Liquids
The Open Burning Test is performed in order to visually (Qualitatively) characterize the behavior and traits of a burning liquid. Twenty (20) milliters of a liquid sample are poured into a 75 mm D x 20 mm H aluminum dish. Attempts are made to ignite the vapors evolved from the sample using a laboratory ignitor or by passing an open flame over the sample. Upon ignition, the resulting burning characteristic — including the flame size, color, and other notable traits — are observed and recorded. The test may be conducted at room temperature until vapor is evolved in flammable concentrations. Higher temperature testing is performed by placing the sample dish or a laboratory hot plate.

Sustained Combustibility Test
The Sustained Combustibility test is used to determine if a substance sustains combustion when heated under the test conditions and exposed to a flame. A metal block with a concave depression (sample well) is heated to a specified temperature. A specified volume of the substance under test is transferred to the well and its ability to sustain combustion is noted after application and subsequent removal of a standard flame under specified conditions.

Chilworth performs the Sustained Combustibility test according to the “United Nations Recommendations on the Transport of Dangerous Goods”, second revised edition, 1995. The apparatus consists of brass block which has a concave well and a pocket drilled to take a thermometer. A small gas jet assembly on a swivel is attached to the block. The block is placed on a hot plate, fitted with a temperature – control device, and heated to the specified temperature.

Flammability Diagram
Under various conditions of temperature and pressure liquids will evolve a certain quantity of vapors. For pure substances the vapors evolved in air at atmospheric pressure may be flammable over a certain range of concentrations defined by the upper and lower flammability limits – the UFL and LFL respectively. If the oxygen (oxidant) concentration in air is reduced the range of flammability is generally reduced. The effect of oxygen (oxidant) concentration on the flammability properties is best represented by plotting a three component flammability diagram showing the effect of oxygen concentration, and inert gas (N2) at atmospheric on the flammability of the vapors or gases.

Chilworth can determine the flammability properties of gases and vapors at atmospheric pressure in general accordance with American Society for Testing and Materials (ASTM) Method E681-94. The method involves creating a uniform mixture of the sample vapors with air (or reduced oxygen concentration) at atmospheric pressure in a closed vessel and attempting to ignite the mixture using an energetic spark ignition source. Trials are repeated for various concentrations of the sample in air (or reduced oxygen concentration) until the concentration that will just sustain flame propagation is determined.