Chilworth Technology perform a wide variety of process safety tests examining explosion hazards (dusts, vapours and gases), thermal stability (powders, liquids and mixtures) and calorimetry.
Many clients are unsure of the exact test, or data, required to solve a specific, identified process problem. Our Laboratories and consulting teams are available to provide assistance to identify the most appropriate tests, in the most cost-effective manner, to provide a solution to your query. This pre-testing consultation (as well as post-testing results discussion) is provided at no extra cost. Chilworth Technology prides itself on the level of customer support it provides.
Every test (except bespoke, one-off investigative tests) are conducted according to Standard Operating Procedures (SOP's).
All tests are performed to a GLP Study Plan or to the principles of GLP (Good Laboratory Practice). This rigorous quality standard is designed to ensure traceability, record keeping, staff training and equipment calibration and maintenance are to the highest standard. Chilworth Technology is unique in providing GLP accreditation to process safety testing.
Chilworth Technology participate in many international “round-robin” calibration studies to verify the consistency of data with other international test laboratories. Results from such studies, where CTL participate, can be provided on request.
Test materials should, as far as is reasonably practical, be those from the plant. This avoids the testing of materials with different specifications and impurity profiles than those actually used on plant.
For dust explosion testing, test standards dictate that materials should be “finest and driest” available on plant. For consistency and conservatism, tests are performed on materials < 10% moisture content and, where the standard methods dictate, less than a specific particle size (typically < 63 micron). Blended powders are processed with caution to avoid separation of materials (eg. by sieving) which could result in unrepresentative materials being tested. When providing samples for test, great care must be exercised to ensure that all samples are truly representative of the bulk material characteristics.
For many applications, reduced versions of a test are available. At Chilworth Technology, unless specifically stated, the test method will be conducted fully in accordance with the Standard Method (eg. EN, IEC, ASTM, etc). In some cases, such as where material is extremely expensive or not readily available, reduced form tests can be conducted to generate specific data. The limitations of such a reduced method must be accepted prior to acceptance of the reduced form result. When comparing tests and results with other data, confirmation must be sought regarding the extent of compliance with the standard method.
All test data generated by Chilworth is fully reported. This includes background information on the material (particle size analysis, moisture content and preliminary thermal screening), full test results and data interpretation to aid in application of the derived result.
Chilworth Technology recognises the critical importance of providing its customers with data which answer their specific concerns. Where a standard test does not exist to provide such data, tailoring of unique testing solutions is regularly undertaken.
Accelerating Rate Calorimetry (ARC)
What Does it Measure? The onset temperature, magnitude, kinetics and pressure effects associated with exothermic activity under adiabatic conditions. The enthalpy of reaction and kinetic parameters can be determined.
Why Do It? The adiabatic nature of the test provides much greater sensitivity than DSC or DTA screening methods, hence requiring a lower safety margin. The kinetics of decomposition, along with time to maximum rate, can be determined. This is an ideal solution for the study of the decomposition of energetic materials owing to the high pressure capability of the test cells (several hundred bar).
Test Standard? No standard exists.
How much material is needed? 10 g
Are there variations of this test available? The test can be conducted in a number of ways. Most common is the heat-wait-search mode for searching for the onset of thermal activity. However isothermal stability tests are also possible.
Limitations? The test is not agitated and, despite being adiabatic, the thermal inertia (phi factor) is relatively high. Without mathematical correction, the data cannot be used for vent sizing or similar safety system design calculations. The test is not suitable for oxidative reactions (smouldering or burning) owing to the limited availability of air – other specialist techniques exist for studying this property eg. Diffusion cell, Aerated cell, Air Over Layer or Basket tests.
Adiabatic Dewar Calorimetry
What Does it Measure? The thermokinetics of runaway reactions under zero heat loss and low thermal inertia conditions using direct simulations of plant failure scenarios. The behaviour of a reaction system during venting can also be determined (ie. whether a reaction tempers or will relieve single or two-phase discharge). The data is used for quantitative consequence analysis and is employed directly in vent sizing calculations using DIERS methods.
Why Do It? The test determines directly the consequences of any credible plant deviation scenario. The quantification of runaway reactions is necessary to generate data for reactor protection system design (eg. vent sizing).
Test Standard? No standard exists.
How much material is needed? 1.5 kg (total batch mass)
Are there variations of this test available? Many! Closed cell tests determine temperature, pressure and time data for failure scenarios. Blowdown and tempering tests determine reaction properties to facilitate the selection of correct vent sizing methods. Tests can be run isothermally, using heat-wait-search, with controlled pumped additions of liquids or gases or with a constant heat input to simulate reactor fire engulfment. Impellor or anchor agitation systems (mechanically coupled) are available. The test can be modified to incorporate a cooling facility for the study of reactions where cooling loss occurs at a pre-defined stage in a semi-batch or batch reaction.
Limitations? The equipment has a pressure limitation of 30 barg. Solids additions are difficult to study.
Aerated Cell Screening Test
What Does it Measure? The Aerated Cell test measures the thermal stability of a powder with forced diffusion of air through the sample. The test can semi-quantitatively determine the onset and magnitude of oxidative (burning) and decomposition events.
Why Do It? The thermal stability of powders can be dramatically affected by the availability of oxygen. For any powder, it is critical to understand the conditions which may lead to exothermic reaction – such that safe processing temperatures can be adequately defined. The Aerated Cell test is specifically designed to simulate forced air passage through a powder (eg. fluid bed drying, rotating drum drier).
Test Standard? No standard exists.
How much material is needed? 150 g
Are there variations of this test available? The test can be run as a preliminary ramped screening test but needs to be run isothermally to provide data for safe drying conditions. A preliminary 25 mm basket test can be used for crude screening of powders.
Limitations? The data requires a safety margin (to account for the effects of scale) and can be applied to volumes up to 1 m3. The test is for powders only - liquids and solids which melt cannot be studied effectively. This is not the best test for decomposition reactions which occur with or without the presence of air.
Air Over Layer Test
What Does it Measure? The Air Over Layer test determines the thermal stability of powder layers (up to 25 mm in depth) that are exposed to a flow of pre-heated air. The test can semi-quantitatively determine the onset and magnitude of oxidative (burning) and decomposition events.
Why Do It? The thermal stability of powders can be dramatically affected by the scale of processing. For any powder, it is critical to understand the conditions which may lead to exothermic reaction – such that safe processing temperatures can be adequately defined. The Air over layer test is specifically designed to simulate the behaviour of powder layers at elevated temperatures exposed to air flow (eg. powders accumulating on hot surfaces (roof of spray dryers or tray drying situations).
Test Standard? No standard exists.
How much material is needed? 100 g
Are there variations of this test available? The test can be run as a preliminary ramped screening test but needs to be run isothermally to provide data for safe drying conditions. A preliminary 25 mm basket test can be used for crude screening of powders.
Limitations? The data requires a safety margin (to account for the effects of scale) and can be applied to volumes up to 1 m3. The test is for powders only - liquids and solids which melt cannot be studied effectively. This is not the best test for decomposition reactions which occur with or without the presence of air.
Bulk Powder (Diffusion Cell) Test
What Does it Measure? The Bulk Powder (diffusion cell) test determines the thermal stability of a powder that has natural diffusion of air through the sample. The test can semi-quantitatively determine the onset and magnitude of oxidative (burning) and decomposition events.
Why Do It? The thermal stability of powders can be dramatically affected by the scale of the process or storage volumes. For any powder being handled at elevated temperature, it is critical to understand the conditions which may lead to exothermic reaction – such that safe storage and processing temperatures can be defined. The Bulk Powder (diffusion cell) test is specifically designed to simulate conditions encountered during powder storage (eg. small silos, Hoppers, FIBC’s) and drying situations where a bulk of powder may exist.
Test Standard? No standard exists.
How much material is needed? 150 g
Are there variations of this test available? The test can be run as a preliminary ramped screening test but needs to be run isothermally to provide data for safe drying and storage conditions. A preliminary 25 mm basket test can be used for crude screening of products.
Limitations? The data requires a safety margin (to account for the effects of scale) and can be applied to volumes up to 1 m3. The test is for powders only - liquids and solids which melt cannot be studied effectively. This is not the best test for decomposition reactions which occur with or without the presence of air.
Carius Tube Thermal Screening
What Does it Measure? The thermal and pressure generation properties of a material when exposed to elevated temperature. The test is a form of Differential Thermal Analysis. This is a high heat loss thermal screening technique. The test measures the onset temperature and magnitude of thermal activity and any pressure events when a material is exposed to elevated temperatures.
Why Do It? Primarily, the test is designed to provide a relatively low cost screening of thermal stability and pressure generation capacity. With an appropriate safety margin, the maximum safe exposure temperature of a material can be specified.
Test Standard? No standard exists.
How much material is needed? 20 g
Are there variations of this test available?
Limitations? The test is not agitated and high heat loss – thus requiring a safety margin. The magnitude of energetic events is measured qualitatively rather than quantitatively. The test is not suitable for oxidative reactions (smouldering or burning) owing to the limited availability of air – other specialist techniques exist for studying this property eg. Diffusion cell, Aerated cell, Air Over Layer or Basket tests.
Determination Of Safe Storage Temperatures For Bulk Materials (Basket Tests)
What Does it Measure? The maximum safe storage temperature of a powder – for any scale of handling or storage – is determined by extrapolating data from a series of three different basket sizes. The critical ignition / no-ignition boundary is determined for each basket size. This data can be scaled-up to any geometry or volume and requires a minimal added safety margin.
Why Do It? Other thermal stability tests for powders require substantial safety margins. The basket series is the most accurate and scalable technique for specifying large scale powder storage temperature limits. Where a material is a borderline candidate for UN 4.2 (self-heating solids) classification, the basket series will provide a definitive classification.
Test Standard? No standard exists.
How much material is needed? 8 kg
Are there variations of this test available? The UN 4.2 Self-heating solids test is a reduced form of this test. Reduced versions, based on individual basket sizes, can be undertaken but will require significant safety margins.
Limitations? The test is applicable to powders which undergo oxidative (burning / smouldering) processes. It is not the best technique for materials which thermally decompose (ie. with or without the presence of oxygen) or for materials with a low melting point.
Differential Scanning Calorimetry (DSC)
What Does it Measure? The thermal properties of a material when exposed to elevated temperature. The range of properties include the onset temperature of decomposition, heat of decomposition, melting point, boiling point, polymorphism, decomposition kinetics and glass transition temperature.
Why Do It? The DSC is a quick and relatively cheap method of thermal screening. It can be used to screen for explosive properties, thermal stability limits and other thermal properties. It consumes a very small sample and is hence useful at early stage product development. Formal kinetic data for decompositions e.g. time to maximum rate (TMR) can be extracted from a small number of tests.
Test Standard? Numerous ASTM standards exist for measuring various properties with DSC.
How much material is needed? <1 g
Are there variations of this test available? The test can be conducted in open (pierced) crucibles or closed high pressure crucibles. Open crucible testing is not normally appropriate for safety applications. An alternative is Differential thermal analysis (eg. Carius tube test) which provides similar safety data.
Limitations? The test does not measure pressure and is not agitated. The data, when used for safety purposes, requires substantial safety margins. Blends / heterogeneous samples are difficult to test reliably owing to the very small sample size in the test. The test is not suitable for oxidative reactions (smouldering or burning) owing to the limited availability of air – other specialist techniques exist for studying this property eg Diffusion cell, Aerated cell, Air Over Layer or Basket tests.
Dust Explosion Severity Test (20 Litre Sphere Test)
What Does it Measure? The 20 L sphere test measures the severity of a dust explosion under ambient conditions. The severity of the explosion is determined by measuring the peak explosion pressure (Pmax), the peak rate of pressure rise (dP/dtmax), from which is derived the explosion severity (dust) constant (Kst) and the explosion severity (dust) class (St 1, 2 or 3).
Why Do It? Explosion severity data is critical in the specification and design of safety systems for explosion protection such as containment (where the peak pressure is required), explosion suppression or explosion venting (where the Kst value is required).
Test Standard? EN 14034 and Kuhner operating manual.
How much material is needed? 750 g
Are there variations of this test available? Yes:
Full test – Triplicate series of tests (typically a minimum of 17 dispersions) – according to the standard this data is required for any plant design.
Single series test – Typically 7 dispersions across a concentration range (not recommended for design).
Limitations? The standard test considers ambient temperature and pressure conditions (although elevated temperature testing is possible). It cannot be used for gases and vapours (although comparable data can be obtained in other equipment).
Alternative uses?
The equipment can also be used to determine the effects of a hybrid (gas or solvent vapour with dust) explosion. Other tests using the 20 litre sphere apparatus are determination of the lowest oxygen concentration at which an explosion can occur (Limiting Oxygen for Combustion (LOC) Test) for specification of inerting system levels (with nitrogen, carbon dioxide, argon or steam inert gas) and the Minimum explosive dust concentration (MEC) can also be determined.
Group A/B Classification Test
What Does it Measure? The test determines whether a powdered solid is capable of producing a flammable dust cloud when dispersed in air at ambient and elevated temperature. Ignition sources for the test are high voltage constant arc, glowing coil and high temperature furnace.
Why Do It? If a dust is flammable (Group A), you need to comply with DSEAR / ATEX 137. Handling the material will then require a suitable Basis of Safety and designation of hazardous zones.
Test Standard? None exists. How much material is needed? 100 g
Are there other versions of this test? Yes – the test can be curtailed to determine flammability at ambient temperature only.
Limitations? The ignition sources employed are "moderately" energetic. The 20 L sphere explosion severity apparatus can be employed for the assessment of high energy ignition sources (up to 10 kJ).
What Does it Measure? The overall heat of reaction and the rate of heat release of a chemical reaction. For batch and semi-batch processes, the plant reaction is simulated under controlled conditions and the heat flow measured throughout. Integration of the heat flow yields the overall heat of reaction and kinetic information on the process.
Why Do It? The principle aim of the test is to quantify the magnitude and rate of heat evolution from a chemical process in order to determine the heat of reaction, understand the kinetics and derive the potential temperature rise from the process. The data finds application in safety assessment and process development and optimisation.
Test Standard? No standard exists.
How much material is needed? 1.5 kg (total batch mass)
Are there variations of this test available? At Chilworth, we can study reactions at temperatures from -30 to +230°C and pressures from ambient to 10 barg. With peripheral equipment, gas flows can be quantified. Reactions at reflux can be studied. Gas / liquid reactions can be fully quantified.
Limitations? The equipment is principally designed for operation under isothermal conditions. Although adiabatic conditions can be studied, this is not optimal equipment (adiabatic Dewar calorimetry is much more reliable). The system is only effective for mobile reaction systems of moderate viscosity.
Layer Ignition Temperature (LIT, Powder Layer)
What Does it Measure? The LIT test determines the lowest temperature of a hot surface that is capable of igniting a 5 mm layer of dust.
Why Do It? Hot surfaces may be a potential source of ignition for powder layers (potentially causing smouldering or flaming). If ‘Avoidance of Ignition Sources’ is the proposed Basis of Safety then it is necessary to know any temperature restrictions that are applicable to electrical equipment and other hot surfaces. The LIT test, when combined with MIT data can be used to define the maximum surface temperature of enclosure for electrical equipment used in hazardous areas.
Test Standard? IEC 61241-2-1 EN50821-2-1
How much material is needed? 300 g
Are there variations of this test available?
Full test – LIT measured to within 10°C
Safety range test = LIT determined at critical levels only (375, 275 and 210°C) for selection of electrical equipment.
Discrete temperature test (eg. tested at one, or a few, selected temperatures only). As employed in the Chilworth DustScreen or CHARP packages.
Limitations? The standard test considers a 5 mm layer depth (this is variable on request). The LIT will be lower as the powder depth increases.
Limiting Oxygen Concentration (LOC)
What Does it Measure? Using a modified 20 L sphere test apparatus to control the atmospheric conditions within the test chamber, the lowest concentration of oxygen (LOC) to support combustion can be defined.
Why Do It? LOC data is critical for the correct setting of oxygen levels when using inert gas atmospheres (nitrogen, CO2, argon or steam) as the proposed Basis of Safety.
Test Standard? EN 14034 and Kuhner operating manual.
How much material is needed? 250 g
Are there variations of this test available? Yes:
Full test – according to the standard this data is required for any plant design.application.
Selected O2 level - such as in DustScreen etc.
Limitations? The standard test considers ambient temperature and pressure conditions (although elevated temperature testing is possible for steam). It cannot be used for gases and vapours (although comparable data can be obtained in other equipment).
Alternative uses? For 20 litre sphere apparatus please see explosion severity tests.
Liquid Conductivity
What Does it Measure? The result of this test indicates the liquid’s ability to conduct electricity, which shows how effectively it can prevent charge separation and generation.
Why Do It? Charge separation naturally occurs in liquids. For low conductivity liquids (such as heptane and toluene) this can lead to the generation of high levels of charge during a range of common process operations. The result can be electrical discharges, which, if flammable liquids are present, can lead to fire or explosion. By measuring conductivity, the risk of this occurring can be predicted and the opportunity provided for addressing the problem, perhaps with a suitable additive. Conductivity measurements can also be used to assess the effectiveness of these additives.
Test Standard? Several standards (including ASTM, BS EN and IEC)
How much material is needed? 500 cm3
Are there variations of this test available? Many standard methods exist and for unusual situations such as limited sample availability, non standard methods can be used.
Limitations? The study of some corrosive liquids is problematical owing to the metal construction of the test cell.
Minimum Ignition Energy Test (MIE)
What Does it Measure? The test measures the minimum discharge energy (in mJ) of an electrostatic (capacitive) or mechanical (inductive) spark capable of igniting a dust cloud at ambient temperature.
Why Do It? If 'Avoidance of Ignition Sources' is the proposed Basis of Safety for a powder handling operation then it is highly advisable to know the MIE of the powder in order to identify potential sources of ignition.
Test Standard? IEC 61241-2-3 or EN 13821 – both standards can be used for electrostatic hazard OR mechanical hazard assessment.
How much material is needed? 250 g
Are there variations of this test available?
Standard test = MIE determined to within 20% (eg. 8 – 10 mJ) for EITHER mechanical or electrostatic discharge sensitivity assessment
Extended test = Standard test for mechanical AND electrostatic discharge assessment
Safety range test = MIE determined at critical levels only (500, 100, 25 and 5 mJ).
Discrete energy test (eg. tested at one selected energy only). As employed in the Chilworth DustScreen or CHARP packages. Note: there are many methods for obtaining the MIE of a dust cloud. Before using this data it is important to establish that the method used is suitable for your application.
Limitations? MIE will reduce dramatically at elevated temperature. Correlations exist to translate ambient results to higher temperature environments. This test is applicable to dusts only (gases and vapours require a related test).
Minimum Ignition Temperature Test (MIT Of Dust Cloud)
What Does it Measure? The MIT test determines the lowest temperature of a hot surface that is capable of igniting a dispersed dust cloud.
Why Do It? Hot surfaces may be a potential source of ignition for flammable dust clouds. If "Avoidance of Ignition Sources" is the proposed Basis of Safety then it is necessary to know any temperature restrictions that are applicable to electrical equipment and other hot surfaces. The MIT test, when combined with LIT data can be used to define the maximum surface temperature of enclosure for electrical equipment used in hazardous areas. The data can also be used in conjunction with MIE (inductance) data to determine the ignition potential of mechanical sparks.
Test Standard? IEC 61241-2-1 / EN 50821-2-1
How much material is needed? 150 g
Are there variations of this test available?
Full test – MIT measured to within 20°C
Safety range test = MIT determined at critical levels only (450, 300 and 203°C).
Discrete temperature test (eg. tested at one, or a few, selected temperatures only). As employed in the Chilworth DustScreen or CHARP packages.
Limitations? The test is only applicable to dust clouds. Data requires a safety margin.
Powder Charge Relaxation Time
What Does it Measure? Charge relaxation time measures, in a very realistic way, how readily a powder dissipates charge.
Why Do It? Essentially this test assesses the same charge dissipation capability of the powder as resistivity, but is a very realistic test in terms of the way charge is actually lost from a powder charged by a process operation. It is therefore complementary to the powder resistivity measurement and usually carried out alongside it as part of a full assessment. Charge relaxation time is particularly good at assessing high resistivity powders.
Test Standard? Many standards exist.
How much material is needed? 250 g
Are there variations of this test available? At Chilworth, this test is performed – as per the standard method – under two relative humidity conditions. Low RH conditions tend to increase resistivity leading to longer charge relaxation times. Testing at a typical ambient humidity, only, is possible, but the results may be misleading if applied to a low RH manufacturing or handling environment.
Powder Chargeability
What does it Measure? Chargeability indicates the propensity for a powder to acquire charge.
Why Do It? The net charge on a powder depends on the rate at which charge is generated and on the rate of charge dissipation. Dissipation is assessed by measuring resistivity and charge relaxation time; charge generation by measuring chargeability. Hence, chargeability should ideally be measured alongside the charge dissipation measurements for a full assessment of the likelihood of a powder acquiring problematic levels of charge, and to maximise the options for addressing such a problem.
Test Standard? No standard exists.
How much material is needed? 1 kg
Are there variations of this test available? The chargeability of a powder varies according to the material it is contacting and the relative humidity. At Chilworth, chargeability is measured against three materials (glass, polyethylene and stainless steel), at two relative humidities (50% and 12%), at three air velocities and at a minimum of 4 powder flow rates. The exhaustive testing program permits ready identification of worst case conditions. Limited tests can be conducted by reducing either the number of materials or only using one RH.
Powder Volume Resistivity
What Does it Measure? Resistivity (the inverse of conductivity) of a bulk powder indicates its ability to conduct (and dissipate) electrostatic charge.
Why Do It? The net charge acquired by a powder depends on both the rate at which charge is generated and the rate of charge dissipation. As a powder’s resistivity indicates its ability to dissipate charge, it is one of the important indicators of a powder’s propensity to acquire and retain charge in practice. Resistivity is therefore one of the key indicators of the severity of electrostatic problems or hazards that must be expected when processing a powder. The results of a resistivity test can also indicate the best approach to addressing such problems.
Test Standard? Many standards exist.
How much material is needed? 250 g
Are there variations of this test available? At Chilworth, these tests are performed – as per the standard method - at two relative humidities. Low RH conditions often increases the resistivity and normally provide a worst case result. Testing at a typical ambient humidity condition, only, is possible, but the results may be misleading if applied to a low RH manufacturing or handling environment.
