CMSE - Blog | Safety Training & Consultancy

CMSE - Blog | Safety Training & Consultancy

12
Apr

Engineering Control Measures to prevent and mitigate explosions

Gary Horgan (CMSE Consultancy Manager at the Chris Mee Group) and his team are outlining the path for companies to ensure they are compliant with Part 8 “Explosive Atmospheres at Places of Work” of the Safety, Health & Welfare at Work (General Application) Regulations 2007 in a series of focussed blogs.

This is blog number 12 in the series, written by Denis Mulcahy which deals with engineering control measures to prevent and mitigate explosions

Engineering Control Measures

When considering the controls to be applied to prevent and mitigate explosions, we can divide them into technical and organizational controls. In this blog we look at technical controls.

Technical controls come under two main headings. These being active and passive control and mitigation systems. Passive control and mitigation systems are generally preferred.

There are a number of schools of thought on how to differentiate between active and passive systems. However, one generally accepted approach is based on whether or not the system requires energy to operate.

Examples of some of passive systems would be to plan the layout of an installation to ensure there is sufficient separation distance between items of plant or equipment.  Similarly, installing bunded areas to control spills or the use of passive fire protection in the form of fire doors / firestopping and fire protection for structural members.

Examples of active systems would be emergency power back-up systems, emergency shutdown systems and active fire protection systems such as water sprinkler / spray systems which are widely used for protection of process and storage vessels, loading installations and warehouses.

Choosing the most appropriate engineering controls is most important. An integral part of this process is selecting good high-integrity plant and equipment and ensuring that explosion safety is fully considered. This is best done at the design stage.

Considerations here may include explosion resistant construction. This may require a vessel to be strong enough to survive maximum explosion pressure in an explosion event, which is generally expensive, or it may be designed for pressure shock resistance which would have a smaller initial cost but may require vessel replacement after an explosion event. Similarly, the use of high-integrity pipework and minimising non-welded joints to minimise releases are other practical examples.

Preventing the formation of an explosive atmosphere is consider as the most desirable of all the controls. This may be achieved by ensuring that the activities carried out do not create an explosible concentration both internally (within a vessel) and externally (around a vessel). One of the most cost effectiveness ways to ensure this is through the use of dilution ventilation. The dilution ventilation may be either by natural ventilation or forced (extract fan) ventilation systems.

However, depending on the process, it may not always possible to control the concentration. An alternative would be to ensure the oxygen concentration is reduced to a level to too low to support combustion. i.e. being below the minimum oxygen concentration (MOC) within a vessel. This can be achieved by adding an inert gas such as nitrogen to the process vessel to displace oxygen. (nitrogen purging). This system may be supplemented by the installation of a gas detection system e.g. fitting an oxygen monitoring system to the vessel as an additional safeguard.

There are numerous other engineering control measures that assist with explosion prevention and mitigation such as Supervisory Control and Data Acquisition (SCADA) Systems and instrumentation monitoring and control systems. These provide information on process variables and may be linked to alarms or automatic shutdown systems.

Mitigation measures may included fire detection systems which detect fire and activate an alarm and / or a sprinkler or deluge system. Explosion suppression systems which detect explosion using pressure sensors (e.g. 10ms/ 0.2 bar).  They rapidly inject an extinguishing medium in to a vessel or enclosure (water, chemical powder, inert gas) and extinguish the flame before significant pressure develops

Explosion venting protects equipment or buildings against excessive internal, explosion-incurred pressures, by means of pressure relief. The explosion vent is designed as weak panel opens at low pressure and vents combustion products. Thus, will relieve the pressure when the opening (or activation) pressure has been exceeded. The combustion products need to vent to a safe location outdoors. The addition of a quench box (Q Box), which is a similar device to a flame arrestor, is required for venting indoors.

 

Chemical suppression barriers use rapid discharge of a chemical explosion suppressant to a duct, pipework or vessel to prevent the flame propagation to other areas. An explosion detector initiates the release of the extinguishing agent when it detects a deflagration pressure or a flame front.

Explosion isolation (slam shut) valves are designed to prevent a pressure wave created inside a vessel or pipework, due to an explosion, from traveling upstream towards to source of the flow. Thus protecting workers, equipment and the facility.

Explosion Diverters which are mechanical explosion isolation devices which protect ductwork and prevent propagation. When an explosion occurs it accelerates down the pipeline and enters the diverter U-bend. Rather than altering its natural flow and change direction, the explosion pressure hits a spring-loaded door in the U-bend which vents to a safe area. When the energy has dissipated, the door will reclose preventing oxygen from entering the pipeline.

Explosion diverter

Rotary valves handle and meter the flow of granular bulk or powders at a controlled feed rate. Material is fed into the valve via a hopper or pipework and passes in discrete packets through the valve rotor to the output side with minimal pressure loss. They work function as airlocks, explosion/flame barriers, and process isolators, among other tasks. 

Flame arresters which function by forcing a flame front through channels which are too narrow to permit the combustion to continue thus extinguishing the flame. These passages can be regular, like wire mesh or a metal plate with punched holes, or irregular, such as those in random packing.

Other simple device include, pressure relief valves and bursting discs which protect vessels and pipework from over pressure.

Last but not least is the selection of electrical equipment suitable for hazardous areas.

The specification is based on the zone designation, the properties of the material being processed and the type of application.

The afore mentioned are just a few examples of the many and varied engineering control measures for consideration when deciding how best to control flammable / explosive atmospheres in the workplace.


Sign up here to receive the next article in this series directly to your inbox before it goes live to the public 

CMSE Consultancy provide professional Occupational, Process, Explosion & Fire Safety Services.

If you require further information or assistance please contact us via email at [email protected], by phone at 021 497 8100 or start an instant chat with us via the chat box in the bottom right-hand corner of your screen.

7
Apr

Common UX Issues With Learning Management Systems and how SAFEWARE have overcome these.

 

For businesses, making the correct decision when it comes to your employees learning and development process is extremely important. Employees deserve the delivery of good quality and engaging training on a secure platform.

 

From branches, learning plans, notifications, reminders and more, check out the key features that SAFEWARE have developed to ensue user experience is top level on the platform. Read more

 

25
Mar

Electrical Ignition Sources

Gary Horgan (CMSE Consultancy Manager at the Chris Mee Group) and his team are outlining the path for companies to ensure they are compliant with Part 8 “Explosive Atmospheres at Places of Work” of the Safety, Health & Welfare at Work (General Application) Regulations 2007 in a series of focussed blogs.

This is blog number 11 in the series, written by Gary Horgan.


Studies of explosion accidents by ignition type have identified that;

  • 8-10% are attributed to electrical arc & sparks and
  • 12% are attributed to hot surfaces, potentially caused by electrical faults within equipment.

So, it can be extrapolated that potentially approx. 20% of explosions can be contributed to electricity. Therefore, it is important that this source of electrical ignition is controlled to prevent explosions in the workplace. When selecting electrical equipment for potential explosive atmosphere (dust, vapours, or gases) it is important that the electrical equipment is selected based on several criteria and you have a clear understanding of the physical properties (Ref. Safety Data Sheets & Product test data). The criteria includes:

Note 1 Gas Group 1G and Dust Group 1D is the highest specification equipment.

Note 2 If you select by mistake a 3D (Zone 22) type equipment for a 2D (Zone 21), this equipment has the potential to ignite a dust cloud atmosphere.

Note 3 Do not install Dust Group equipment 1D,2D or 3D in gas and vapour explosive atmosphere if not rated.

 

2              Select the correct electrical equipment, Gas Group based on the Minimum Ignition Energy (MIE measured in mJ) of the dust, vapours, or gases at your workplace;

Gas & Vapours

 

Note 1 IIC equipment is the highest specification equipment for gases and vapours.

Note 2 Selecting the incorrect Gas Group i.e., IIA (methane) say in a hydrogen area (IIC) has the potential to ignite a flammable hydrogen gas mixture.

Dust

 

 

3              Select the correct electrical equipment based on Auto-Ignition Temperature (AIT degrees OC) of the dust, vapours, or gases at your workplace;

Note 1 Selecting the incorrect Temperature Class has the potential to ignite a flammable dust, vapours, or gases atmosphere.

Note 2 When you are dealing with dust and there is a potential for equipment to be covered you must also consider the effect of the dust layer cover. As a guide for a dust layer cover depth of 5mm you should reduce the Auto-Ignition Temperature by a factor of 0.66. So, for example if you know your powder has an AIT, T1 is 4500C, then 450 x 0.66= 2970C, so therefore you should select a T3 rated equipment which has an ignition temperature between 200 – 3000C.

Sample Ex Equipment Label

To summarise this label based on what I discussed earlier in this blog:

II             Above ground type installation (not a below ground mine),

1GD       Category 1 equipment (Zone 0 & 20) suitable for Gas, Vapour and Dust explosive atmosphere,

EEx         Conforms to European Ex-standards,

IIC           Gas Group C, MIE; 0.001mJ,

T4           Auto-Ignition Temperature Class, suitable for ignition temperature range >130 – 200OC.


Sign up here to receive the next article in this series directly to your inbox before it goes live to the public 

CMSE Consultancy provide professional Occupational, Process, Explosion & Fire Safety Services.

If you require further information or assistance please contact us via email at [email protected], by phone at 021 497 8100 or start an instant chat with us via the chat box in the bottom right-hand corner of your screen.

18
Mar

Non Electrical Ignition Sources

Gary Horgan (CMSE Consultancy Manager at the Chris Mee Group) and his team are outlining the path for companies to ensure they are compliant with Part 8 “Explosive Atmospheres at Places of Work” of the Safety, Health & Welfare at Work (General Application) Regulations 2007 in a series of focussed blogs.

This is blog number 10 in the series, written by Denis Mulcahy.


Non Electrical Ignition Sources

Here we look at non electrical ignition sources. In order to prevent the ignition of a hazardous explosive atmosphere, it is necessary to be aware of all possible ignition sources that may occur and to ensure that these ignition sources cannot become effective.  Some of ignition sources that should be considered are:

 

Hot surfaces

If an explosive atmosphere i.e. a gas, vapour or dust cloud, comes into contact with a heated surface, ignition can occur. A dust layer in contact with a hot surface may give off decomposition gases that form an explosive atmosphere, similarly where the dust ignites, glowing particles may be carried by transfer systems and act as an ignition source where an explosive atmosphere present in a different location. This ignition may occur a significant distance from the initial hot surface.

 

Flames and hot gases (including hot particles)

Flames, are among the most effective ignition sources and are associated with combustion reactions at temperatures of more than 1000 °C.

Hot gases are produced as reaction products these can also ignite an explosive atmosphere.

In the case of sooty flames, glowing solid particles are also produced. These may be carried by convection currents and provide an ignition source elsewhere.

 

Mechanically generated sparks

As a result of friction, impact or abrasion processes, such as grinding, particles can become

separated and become hot due to the energy applied. If these particles consist of oxidizable substances, e.g. iron or steel, they can undergo an oxidation process, thus reaching even higher temperatures. These particles (sparks) can ignite combustible gases and vapours and certain dust/air mixtures.

 

Radio Frequency (RF) Electromagnetic waves

Electromagnetic waves are emitted by all systems that generate and use high-frequency electrical energy (high-frequency systems ranging from 104 Hz to 3 x 1012 Hz) e.g. radio transmitters, some medical equipment or industrial RF generators for heating, drying, hardening, welding, cutting, etc. should be considered. All conductive parts located in the radiation field act as receiving aerials. If the received radio-frequency power density is large enough and the receiving aerial is sufficiently large, it can cause thin wires glow or generate sparks when conductive parts make contact. This can cause ignition of an explosive atmospheres.

 

Electromagnetic waves

Radiation with frequencies ranging from 3 × 1011 Hz to 3 × 1015 Hz, particularly when focussed, can become a source of ignition. This is due to absorption in explosive atmospheres or on solid surfaces. Sunlight, for example, can trigger an ignition if reflective objects cause a convergence of the radiation.  In the case of laser radiation, even at large distances, the energy (power density) of even an unfocused beam can make ignition possible.  When the laser beam strikes a solid body surface or dust particles in the atmosphere, energy is absorbed and a heating process occurs.

 

Ionizing radiation

Ionizing radiation can ignite explosive atmospheres (especially dust particles) as a result of energy absorption. Ionizing radiation can cause chemical decomposition or other reactions, which can lead to the generation of highly reactive radicals or unstable chemical compounds. This can cause ignition.

 

Ultrasonic Sources

When ultrasonic sound waves are used, a large proportion of the energy emitted by the electroacoustic transducer is absorbed by solid or liquid substances. As a result, the substance heats up so intensely that, in extreme cases, ignition can be induced

 

Adiabatic compression and shock waves

In the case of adiabatic or almost adiabatic compression and in shock waves, high temperatures

can occur which can ignite explosive atmospheres. For example, in diesel engines compression ratio must increase the temperature in the cylinder sufficiently to ignite the fuel / air mixture using compression. In air compressors lines and containers connected to these lines, explosions can occur as a result of a compressive ignition of lubricating oil mists due to the operation of quick-acting valves in long pipes.

 

Exothermic reactions, including self-ignition

With exothermic reactions, if the rate of heat generation exceeds the rate of heat loss to the surroundings. The high temperatures can lead to both the initiation of smouldering and/or burning

and the ignition of explosive atmospheres.  Decomposition of animal fodder and other organic compounds, decomposition of organic peroxides, polymerization reactions, exposure of some metals dusts / powders to air can induce self-heating leading to self-ignition.

 

Equipment in Hazardous Areas

Auto ignition temperatures of the different explosive mixtures vary considerably. They are classified and divided into temperature classes in IEC 60079-20-1 as shown in Table 1.

Table 1: Temperature classifications

When considering installations that pose a risk of igniting an explosive atmosphere.  The equipment used is classified under 3 Groups. Group I refers to equipment used in below ground (i.e. Mining), Group II equipment above ground where gases / vapours may be present. Group III equipment above ground where dusts may be present.

Group II equipment has subgroups based on the amount of energy required to ignite the gas / air mixture. Group III equipment has subgroups based on the type of dust and the potential energy release during combustion. These are shown in Table 2.

Examples of potential non electrical ignition sources

Electromagnet Radiation from Mobile Phones can be a potential source of ignition. IEC 60079-0 specifies max levels of Radio Frequency emissions for the equipment groups, a typical non Ex (Explosive) rated phones RF outputs is 2-4 watts. Table 3 shows potentially incendive RF outputs for the relevant equipment groups

The RF outputs from mobile phones can be potentially incendive for solvent vapours and gases which come under equipment group IIB and IIC.

Group II B typically includes Ethylene, Ethylene oxide, Ethylene glycol, Hydrogen sulphide, Ethyl ether and Town gas (Methane),

Group II C typically includes Hydrogen, Acetylene and Carbon disulphide.

 

Friction due Bearing Failures

Overheating is generally the result of excessive operating temperatures and improper lubrication.

Higher temperatures also reduce the hardness of the metal, causing early failure.

Example 1

On the evening of September 12, 2017, a ferry’s main engine exploded and burned five running hours after a rebuild.  The engineer standing near the engine at the time of the blast, suffered severe burns to his hands and face. An investigation found that a bearing shell had spun on a main bearing blocking the flow of lubricating oil. The conn rod’s big end seized breaking the big end’s bearing bolts. The rod then went through the wall of the crankcase and the lube oil gallery, leading to the explosion.  The investigation found high quantities of particulate matter, including unusually large particles of 1mm or greater in the oil filter. This debris may have entered the engine during the three days it was at the site and disassembled prior to installation.

Example 2

Imperial Sugar facility in Georgia, a conveyor belt running between sugar storage silos was enclosed to help prevent the contamination of the sugar on the belt and reduce the amount of dust that needed to be cleaned from the underground tunnels. This caused a cloud of sugar dust built up inside the enclosed conveyor. A blockage caused sugar to spill on to the conveyor bearings one of which overheated and ignited the sugar dust cloud in the enclosed conveyor. The containment caused the explosion to build enough pressure to push it throughout the rest of the building, leading to secondary explosions that caused 14 workers to be killed. The possibility of a dust explosion was not even considered when building enclosing these conveyor belts, even though management at the plant should have been very well aware of the combustibility of sugar dust.

Figure 1: Conveyor explosion

Damage after the catastrophic dust explosion at the Imperial Sugar Co. shown in figure 2

Figure 2: Dust explosion damage

Overview of Dust Ignitions

Figure 5: Dust ignitions by industry

In reviewing the global incident data from Dust Safety Science, food and wood products made up over 65% of the combustible dust fires and explosions recorded. These materials also resulted in 59% of the injuries and 62% of the fatalities. A breakdown of the fires, explosions, injuries and fatalities for each type of material is given as follows: 

Figure 6: Fires, explosions, injuries and fatalities

Equipment and Causes

Dust collectors demonstrate the highest percentage of combustible dust incidents with 59 fires and 12 explosions reported in 2019. This is lower than the historic data from the CSB, which suggests up to 40%.

Figure 7: Equipment and Causes

Explosion Prevention & Mitigation

Minimise accumulations of flammables and keep concentration below LEL. Minimise potential sources of ignition and implement suitable monitoring systems for equipment and processes. Maintain spatial separation between accumulations and ignition risks where practical. Design for full confinement in the event of an explosion. Full or partial system inerting. Installation of automatic explosion suppression systems, flame front diverters; explosion venting systems. Passive flap, float and rotary valves.

Examples of explosion prevention & mitigation measures are provided below

Explosion Isolation via flap, float or rotary valves

Sign up here to receive the next article in this series directly to your inbox before it goes live to the public 

CMSE Consultancy provide professional Occupational, Process, Explosion & Fire Safety Services.

If you require further information or assistance please contact us via email at [email protected], by phone at 021 497 8100 or start an instant chat with us via the chat box in the bottom right-hand corner of your screen.

9
Mar

Strong demand for H&S professionals – Health & Safety Review

Salaries for health and safety professionals are holding steady and demand for their services is generally strong, despite – or even because of – the pandemic. But not all sectors are weathering the Covid-19 storm well.

CMSE Consultancy Manager Darren O’Keeffe and CMSE Recruitment Manager Odhran Molloy discuss the demand for health and safety professionals and the differing circumstances apply across the various industry sectors.

Read Full Article Health & Safety Review Article Here


You may also be interested in:

Have a question? Chat to us instantly by clicking the chat box in the bottom right-hand corner of your screen. Alternatively, you can click here to email [email protected]