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2
Mar

Static Electricity as an Ignition Source

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 9 in the series, written by Denis Mulcahy.


When we consider potential ignition sources we may think of open flames and sparks from grinding and welding operations, which are a significant contributor to the ignition of flammable or explosive atmospheres, accounting for approximately 22% of all ignitions.  However, static electricity also accounts for approximately 22% of all ignitions.

  1. Creation of electrostatic charges

An electrostatic charge occurs whenever two surfaces are separated, where at least one of them is highly electrically insulating. When two surfaces come into contact, a redistribution of charge carriers takes place. The phenomenon applies to both solids and liquids depending on electrical conductivities.

People can become charged by walking across a room where either the carpet or their shoes are nonconductive. High charges can also be created on conveyor belts and during the unwinding of plastic films. When a powder is unloaded, conveyed through a pipe, is sifted, or fed through a funnel, the powder and equipment will probably become charged.  Similarly, with liquids, flow through pipes or hoses, stirring, spraying or liquid atomization, will probably cause both the liquid and equipment be become charged.

The charge level may be increased for liquid flow through filters or where multiphase mixtures are handled.  For example, liquids that contain suspended solid particles or droplets of an immiscible liquid, the charge level will probably increase by several orders of magnitude.

 

  1. Types of Electrostatic Discharges

2.1. Spark discharges

A spark discharge can occur when the charge potential rises to the point where the dielectric strength (resistance) of the air is reached across a suitable sparking gap to an earthed object.

The energy W of such a spark discharge can be calculated with the formula W = ½ CU2 where C represents the capacitance of the insulated, conductive object and U its potential.

 

The ignition danger is assessed by comparing the discharge energy with the minimum ignition energy of the potentially explosive atmosphere present.  This will show that flammable gases, vapours, and dusts can be ignited by spark discharges.

Figure 1 Spark discharge

Where charges are restricted to nonconductive surfaces, they cannot be dissipated in the form of a single spark discharge. Under these circumstances, there are three other types of discharge that may take place.

 

2.2. Brush and corona discharges

Where the surface of an insulator has charges of one polarity which are raised to the level equal to or greater than the dielectric strength of air (approx. 3× 106 V/m). A static discharge can occur when surface of an earthed electrode (e.g. person’s finger) nears the surface.

 

Corona discharges generally occur if the electrode’s diameter is approx. 1 to 5mm. For larger electrodes brush discharges are more probable. For hazard assessment, the worst-case i.e. a brush discharge is usually considered.

Figure 2: Corona discharge

Brush discharges can also be expected when an earthed, conductive electrode enters a high-strength electric field.  The electric field may be created by a highly charged insulating liquid or suspension, a mist, a pile of insulating bulk solids, or a dust cloud.

Figure 3: Brush discharge

The characteristic properties and incendivity of brush discharges have been studied by many authors. The figures stated in the literature for the equivalent energy of brush discharges, which were determined with explosive gas/air mixtures, are on the order of a few millijoules.

 

The incendivity of bush discharges depends on the electrode’s radius of curvature, the polarity of the electric field, and – if the electric field emanates from a charged plastics surface – the surface charge density and size of the charged surface area.

 

Energy released from brush discharges is assumed to have the potential to ignite explosive gas/air mixtures, vapour/air mixtures and hybrid mixtures but are very unlikely to ignite pure dust clouds.

 

2.3. Propagating brush discharges

Where charges of opposite polarity occur on the opposing surfaces of an insulating sheet, propagating brush discharges can occur.  They are caused by an electrical short circuit between the two oppositely charged surfaces of the sheet.  

These can typically arise when:

 

  • When two electrically connected electrodes approach the respective surfaces or

or

  • Mechanical perforation of the sheet

or

  • Electric perforation of the sheet i.e where the charge density is sufficient to overcome the resistance posed by the weakest point in insulating sheet.

 

The resulting brush discharge forms a bright central discharge and many discharge channels propagate outward along the surface point like the spokes of a wheel on both sides

Figure 4: Propagating brush discharge

The energy released by propagating brush discharges is normally sufficient to ignite potentially explosive gas/air, solvent-vapour/air, and dust/air mixtures.

 

Persons may suffer serious shock if, for example, they initiate a propagating brush discharge by inadvertently touching a highly charged surface. Efforts must be taken to exclude this kind of discharge wherever potentially explosive gas, vapour or dust atmospheres can form.

 

2.4. Cone discharges

These discharges may occur when charged and highly insulating solids i.e. with volume resistivities greater than 1010 ohms·m are filled into silos and containers. Although silos may be conductive, and earthed, for highly resistive solids subjected to high filling rates, the charge dissipation time may not be sufficient. The charges on the surface of the solids may accumulate to a point where the dielectric strength (resistance) of the air within the silo is reached and the solids are piled and form a suitable gap to allow a discharge from the surface of the solids to the earthed side of the silo.

  1. Controlling Static Electricity

Earthing & Bonding

The most important protective measure is to connect and earth all conductive parts that might become dangerously charged.

 

Some examples of earthing and bonding arrangements

However, if nonconductive parts and materials are present, earthing and bonding may not be enough. In such cases, dangerous charging of nonconductive parts and substances (including solids, liquids and dusts) must be excluded by other means such as

  • Control of filling velocity
  • Avoiding splashing – fill from the bottom.
  • If mixing liquids consider density and miscibility.
  • Consider charge relaxation time for non-conductive liquids or resistive solids
  • Use of static dissipative additives to assist with charge relaxation.
  • Use Static Dissipative Floors however, if the floor is not conductive, a grounded mat may be used.
  • Use anti- static PPE
  • Earth Continuity Testing

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CMSE Consultancy  provide a professional Health, 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.

26
Feb

HSA update the COMAH guidance for land use planning consultation

The Health and Safety Authority (HSA) have recently issued new guidance on Technical Land-use Planning Advice to reflect changes in the Control of Major Accident Hazards (COMAH) Regulations of 2015 (in turn reflecting the Seveso Directive [2012/18/EU]). The HSA have sent out a public consultation request with a closing submission date of the 19th of March 2021. 

What is new about the guidance?

The HSA have set out the policy and practice in the provision of technical land-use planning advice to Planning Authorities. It will replace the current guidance document – Policy & Approach of the HSA to COMAH Risk-based Land Use Planning; 19 March 2010.

The new guidance will reflect the changes in the 2015 COMAH Regulation in relation to Land-Use Planning (LUP), significant modifications at COMAH establishments and on related public information and consultation provisions. It will set out a risk-based approach to generating Technical Land-Use Planning Advice (TLUP).  

Some of the changes in the revised guidance include:

  • Clear guidance is given for major accident scenarios that are to be considered relevant to TLUP, their frequencies of occurrence and the modelling parameters to be used. The Guidance consistently and closely follows the approach set out in the event trees in the Purple Book1 and BEVI2 (which describe a risk-based fatality approach for COMAH establishments, and which forms the basis for the system of risk assessment and ultimately, land-use planning in the Netherlands).
  • Regulation 24 – the land-use planning regulation and the link to planning and development, is explained.
  • Additional sections have been added on the LNG, Recovered Natural Gas (RNG) and Distillery/Warehouse sectors– and future new sections can be slotted into the framework as new sectors emerge.
  • Central Competent Authority (CCA) will set a risk-based Consultation Distance and the approach that will be taken if the CD risk level does not extend beyond the site boundary.

Further information on the above is available here


CMSE Consultancy specialists provide practical solutions and advice to all our clients in the SEVESO Safety services area.

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]

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10
Feb

HAC of Liquids Gases Vapours

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 8 in the series.

Introduction

In this blog, we will be discussing the process for the Hazardous Area Classification for the handling of flammable liquids, gases, and vapours.

As we discussed previously for dusts, Hazardous Area Classification is a process used to assess an area to determine the likelihood that a flammable atmosphere will occur and the duration that it’s likely to occur for.

Why is Hazardous Area Classification Important?

In all EU Member States, it is a requirement for all workplaces handling flammable materials to undertake this process as part of the ATEX Workplace Directive (ATEX 137). In Ireland, this mandatory legal requirement is transposed into Irish law by Regulation 170 of the General Application Regulations 2007:

One of the main reasons for hazardous area classification is to help employers choose safe equipment and processes for specific locations.  Standard electrical and electronic equipment produce sparks and heat both during normal operation and when they malfunction.  Some clothing fabrics can generate static on their surface which can then discharge, similarly, a spark could be generated as a result of impact of hand tools on a surface. 

There are many other potential ignition sources. If sparks are introduced in locations where an explosive atmosphere could be present, it could lead to fire or explosion

Description of Zones

So, the regulations refer to specific “zones” for areas that are identified as being hazardous. These are:

General guidance on how to determine the location and extent of these zones is available in the engineering standard EN 60079-10-1:2015. There are also industry specific guides and standards available for specific types of processes and facilities, such as the Energy Institute’s “Model Code of Safe Practice Part 15 for the oil and gas industry.

It is important that this is carried out by someone who is competent to do so, as it often requires calculations to be carried out using the explosive characteristics of the material and the available ventilation.

Effect of Ventilation on Zones

Where potentially flammable atmospheres arise, ventilation in the area can have a large impact on the type and extent of the hazardous zone. Ventilation may be either natural or artificial. Natural ventilation is the movement of air by wind or temperature gradients. Artificial ventilation is caused by fans, extractors etc. With the use of artificial ventilation, it is possible to achieve;

  • Reduction in the type and/or extent of zones;
  • Shortening of the time of persistence of an explosive atmosphere;
  • Prevention of the generation of an explosive atmosphere.

Engineering standard EN 60079-10-1:2015 includes the following table which summarises the potential effect of the available ventilation on the type of zone:

Example of Hazardous Area Classification

In our ATEX awareness training, we often use a petrol station as a useful example to illustrate how hazardous area classification may work in practice.

As can be seen in the graphic above (adapted from HSA website), a Zone 0 is often identified in the headspace of tanks containing flammable liquids which are being stored at or above their flashpoint. In this case Zone 0s are identified in the headspace of the road tanker storage tank and the below ground fuel storage tank, as an explosive atmosphere will be present continuously.

Zone 1s are identified around filling/dispensing points (with an approximately 1 – 1.5m radius), such as around the connectors on the road tanker and the petrol pump filling head, as it is likely that a potentially explosive atmosphere will be present in these areas during filling operations. A Zone 1 is also identified around the gas release vents in the top of the road tanker.

Zone 2s are identified for a larger extent around the Zone 1s, as in the event of a maloperation such as a spillage of petrol. The release point would be the same, but the volume of a potentially explosive atmosphere will be larger. The size of the Zone 2 will be, in part, based on the maximum credible volume of petrol that could be released in a spill.


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
Feb

We check in with CMSE Recruitment Manager Odhran Molloy

With COVID-19 public health restrictions for the past year, there has been a lot of uncertainty across all sectors and industries.
The last few months have shown us that while 2021 has a lot of unique challenges, the EHS Recruitment industry has been lucky enough to have remained busy and very fast paced.
There are a lot of opportunities in the market at the moment with many different projects across the country. People from all different experience levels are being placed in contract and permanent positions. 
 

CMSE Recruitment is a very professional organisation that maintains a dedicated and personal approach. I really appreciated the tips and rehearsal prior to the interviews. With them, going the extra mile for you is not just the exception but the routine. You can even feel the smile while calling late on a Friday evening! You are fantastic. Thank you”.

 Olivier Gardelle,

Olivier Gardelle,

H&S Specialist
Kraft Foods Group

I have used the services of CMSE Recruitment on a number of occasions. They provided me with excellent candidates and we have recruited two Site Safety Advisors who are working on various projects within our company. I found the service and calibre of candidates excellent. I would highly recommend CMSE Recruitment.

 Louise O'Loughlin

Louise O’Loughlin

Human Resources,
ESBI


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5
Feb

What are the hazards of liquid nitrogen and why should we be concerned?

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 Health, Safety & Welfare at Work (General Applications) Regulation 2007 in a series of focussed blogs.


Liquid nitrogen (N2) is a form of nitrogen gas which is inert, colorless, non-irritating and odorless. At extremely low temperatures (-195oC) it forms a liquid and is referred to as a cryogenic liquid. An important consideration of cryogenic liquids is their ability to produce large amounts of gas when vaporized.

Liquid nitrogen has many industrial uses, including:

  • Freezing and transport of food products
  • Preservation of biological samples
  • The shielding of materials from oxygen exposure
  • Cooling of materials for easier machining

For industrial use, liquid nitrogen is primarily stored and handled in cryogenic liquid cylinders and cryogenic storage tanks. However, releases of liquid nitrogen during a process can occur unexpectedly leading to severe health effect exposure to people in the workplace. The most common sources of gas release may occur through a variety of processes, such as:

  • Natural release i.e. from cryogenic tanks or flasks, through evaporation from non-pressurized containers or pressure relief valve from pressurized containers.
  • Release when used for routine processes. For example, processes include chilling and freezing operations or tank relief valves.
  • Unintentional release due to leaks from pipework and valves.

With each above scenario consideration on the potential risk and hazards of liquid nitrogen exposure is necessary.

What are the main hazards associated with the use of Liquid Nitrogen?

Nitrogen gas is often referred to as a “silent killer” as there is no warning to humans (such as taste, smell) when exposure occurs. Therefore, it is important to understand the main hazards associated with using liquid nitrogen. Most common hazards include:

  1. Asphyxiation

Nitrogen gas is known as a simple asphyxiant. These gases are likely to be a danger when the concentration in inhaled air is substantial enough to cause a reduction in oxygen levels in the atmosphere. If the level of O2 in the atmosphere is reduced to below 18% this can lead to rapid breathing followed by loss of consciousness and death when levels reduce further.

Below is a summary of the effects of reduced O2 in the atmosphere:  

Source: BCGA GUIDANCE NOTE GN11 Use of Gases in the Workplace: The management of risks associated with reduced oxygen atmospheres

There are some factors which may increase the risk of a reduced oxygen atmosphere in the workplace, such as:

  • Volume of air within the workplace. i.e. dangers of working in confined space where oxygen may be lacking due to displacement of air by another gas.   
  • Ventilation in the workplace (fresh air change rate)
  • The volume and rate of the gas released

2. Frostbite and cold burns

Liquid nitrogen can cause significant damage and burns when in contact with the skin.

3. Explosion due to system pressurisation

When heat is applied to liquid nitrogen the pressure in the vessel or container will build up causing rapid expansion generating nitrogen gas. If liquid nitrogen is contained in a sealed or poorly vented system this will cause an explosion.

Fortunately, the reported incidents of adverse workplace exposure to N2 have remained low in Ireland. Nonetheless, it is important not to be complacent as the consequences of such incidents can be significant. In January 2021, six people unfortunately died while working at a food processing plant based in the US due to exposure to liquid nitrogen. Although the case remains under investigation, it is suspected the incident occurred due to a leak of a cryogenic freezing system where the poultry is processed.

Another significant incident of note occurred back in 2000 where a lab worker at a UK based medical research facility died from asphyxiation due to exposure to liquid nitrogen. The leak occurred in a freezer room, which caused the oxygen in the air to become depleted. Findings from the investigation concluded the cause of the exposure was due to inadequate ventilation and failure to install monitoring systems for detecting nitrogen in the room atmosphere.  

What does the employer need to do?

With any hazard in the work place the employer should always evaluate the level of risk with consideration to the Hierarchy of Controls. Asking the right questions can be beneficial in determining control measures. Can the process or substance be eliminated or substituted? Are there engineering controls to be considered i.e. isolation, ventilation? Are employees sufficiently trained i.e. work permits? When should RPE and PPE be worn?

Risk assessments, monitoring systems and emergency procedures are also essential control measures in preventing adverse N2 exposure in the workplace. Most importantly, the employer must ensure they provide adequate information, instruction and training to employees working with liquid nitrogen.

CMSE Consultancy can assist you in determining/ calculating potential hazards posed by N2 in your workplace in accordance with BCGA GUIDANCE NOTE GN11 Use of Gases in the Workplace: The management of risks associated with reduced oxygen atmospheres.

Further interesting information is available on our weekly  Process Safety Blogs.

 

 

CMSE Consultancy  provide a professional Health, 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.

Information on Chris Mee Group's response to the Containment Phase of the Coronavirus [COVID-19] Outbreak.Read More
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