DSEAR awareness

Steve Manchester Director

Fire Safety Group

Part of the BRE Trust

Handling flammable gases, liquids and dusts: ensuring DSEAR compliance.Steve Manchester CEng MIFireEFire Safety Group

What we are trying to prevent

Legislation

European ATEX Directives

There are two European Directives relating to potentially explosible atmospheres:

⚫ATEX 100a Equipment Directive (94/9/EC) - Due to be replaced soon with a new number. No changes to Essential Health and Safety Requirements of the Directive. Changes affect Notified Bodies rather than manufacturers.

⚫ATEX 137 User Directive (99/92/EC)

Equipment and Protective Systems Intended for use in Potentially Explosive Atmospheres Regulations 1996

In the UK, the legislation that implements the ATEX 100a Equipment Directive.

Focuses on equipment being manufactured to suitable safety standards, based on the nature of the flammable atmosphere and it duration in the area where the equipment is located.

Dangerous Substances & Explosive Atmospheres Regulations 2002 (DSEAR)

These are the UK regulations that enforce the European ATEX 137 User Directive and the safety aspects of the Chemical Agents Directive.

Sets out minimum requirements for the protection of workers from fire/explosion risks arising from dangerous substances and potentially explosive atmospheres

Came into force 1st July 2003.

Scope

DSEAR applies wherever:

• A dangerous substance is present or liable to be present in a workplace.

• The substance presents a risk to the safety of persons (not health).

Workplace means any premises where a work activity is carried out.

Workplaces covered

• Industrial/commercial premises

• Landbased/offshore installation

• Vehicles/vessels

• Industrial estates/business parks

• Houses/domestic dwellings

• Laboratories

Dangerous substance

In the context of the regulations the term “dangerous substances” means anything with the potential to create a risk to persons:

• Fires

• Explosions

• Thermal runaway from exothermic reactions

• Self-heating (spontaneous combustion)

Note: It is not only the property of the substance that needs to be assessed but also how it is being used/processed.

Explosive atmospheres

Explosive atmospheres are defined as a mixture with air, under atmospheric conditions, of flammable substances in the form of :

• Gases

• Vapours

• Mists

• Dusts

Dangerous Substances

Examples:

• Petrol

• LPG (propane, butane)

• Methane, hydrogen,

• Solvents

• Metal powders (aluminium, magnesium)

• Foodstuffs (flour, coffee, sugar etc)

• Pharmaceuticals

• Chemicals

• Coal

Dusts

Conditions for a dust explosion

• dust must be combustible

• dust must be dispersed as a cloud

• particle size distribution capable of propagating flame

• concentration must be in explosible range

• an ignition source must be present

• the atmosphere must support combustion

Dust explosions

Characteristics of dust explosions

• Pressure up to 10 bar

• Long flame projection

• Toxic gases

• Primary explosion

• Secondary explosion

• Turbulence effects pressures

Primary explosion

• Most dust explosions that occur are relatively small and do little damage.

• They usually start inside equipment where there are dust clouds present for long periods.

• Explosion protection equipment should ensure such events do not escalate.

• Relatively little or no damage should result and no injuries, as long as the protection system is correctly chosen and maintained.

Secondary explosion

• If the explosion inside the equipment, which is inside a building, is not mitigated the pressures can dislodge dust in the building, present due to poor housekeeping.

• A much larger dust cloud is created filling part of whole of the building that is then ignited from the flame front of the primary explosion.

• This causes severe damage to the building and increases the risk of injury/fatality.

Commonly used tests

• Classification

• 5mm layer ignition

• Minimum ignition temperature

• Minimum explosible concentration

• Minimum ignition energy

• Limiting oxygen concentration

• Explosion indices (maximum pressure/Kst/St. Classification)

• Burning number (BZ or classification)

• Air-over layer

• Diffusion cell

• Charge decay/relaxation

Examples of explosible powders• Foodstuffs (sugar, flour, coffee)

• Metals

• Coal/carbon

• Chemicals

• Pharmaceuticals

• Dye stuffs

• Dried sewage sludge

• Meat & Bone Meal

• Rubber

• Plastics

Basically any organic material in powder form!

GASES/VAPOURS

Characteristics of gas explosion

• Faster (than dust) rate of pressure rise

• Potentially more damage

• Specific concentration range for ignition

• Pressure wave followed by flamefront

• Deflagration more common than detonation

• Turbulence effects pressures

Conditions for a gas/vapour explosion

• Gas/vapour must be combustible

• must be dispersed as a cloud or could be a vapour layer

• concentration must be in explosible range

• an ignition source must be present

• the atmosphere must support combustion, i.e. enough oxygen.

DSEAR

Duties under these Regulations

The regulations place duties on employers to assess and control the risks from dangerous substances.

In addition to their own employees, this duty extends to:

• Contractors working on-site• Visitors• Members of the public

The duty does not extend to provision of training unless they are on the employers premises.

Main action areas of DSEAR

The important areas of the regulations are :

• Risk assessment

• Measures to eliminate/reduce identified risks

• Hazardous area zoning

• Provision of suitable equipment/safety systems

• Information and training to employees

Risk assessment

The significant findings will need to be recorded.

1. Identify the hazardous substances

2. Identify ignition sources

3. Describe organisational/technical measures taken to control risk

4. The scale of the anticipated effects (Evaluation).

5. Additional mitigation measures taken to reduce risk to an acceptable level.

The risk assessment is a ‘live’ document and MUST be kept up to date when significant changes are made to the process.

Risk evaluation

From all the gathered information an evaluation must be undertaken on all the operations and areas, to enable those work activities of high risk to be identified.

This could take into account such factors as:

• Likelihood of the hazard occurring• Severity - terms of injuries and economic• Who is at risk – employees, visitors, neighbours• Risk factor – e.g. high/medium/low risk• Actions

Risk mitigation

Where the risk is unacceptable mitigation measures are required by DSEAR and could include :

• Reducing the numbers of employees exposed.

• Providing plant that is explosion resistant.

• Providing explosion suppression or relief.

• Providing explosion isolation devices.

• Providing suitable Personal Protective Equipment (PPE).

Explosion protection

• Venting

• Suppression

• Inerting

• Containment

• Isolation

Venting

• Most common method used for protection.

• Weak areas of the vessel designed to open at an early stage in the explosion.

• Burning materials and combustion products released.

• Size of vent related to explosion severity (Kst), vessel volume, residual strength of vessel (Pred) and vent opening pressure (Pstat).

Venting

• Vents must be able to open!!!

• Venting must be to a safe area

Venting

• Must be located in a safe area!

Safe venting area

• Flame lengths are long

• Safe area required!!!!!

Suppression

Quick acting explosion protection systems that act by early detection of the explosion that activates the injection of a suppressant material from a high pressure bottle.

• More expensive that venting

• Used when location means venting not suitable

• Must be maintained

Inerting

Reducing the oxygen concentration to a level which will not support combustion.

The value is determined by the limiting oxygen concentration (LOC) test.

Nitrogen and carbon dioxide are the usual inert gases used.

Safe operating levels should be 2% below the LOC value.

Containment

• Process vessels built to withstand an explosion.

• Pressure resistant - no deformation.

• Pressure shock resistant – liable to permanent deformation but won’t break.

• Usually used to contain toxic materials or for relatively small vessels such as mills.

Isolation

Measures designed to stop explosions initiated in one plant item propagating to another via ducts and pipes.

– Slam-shut valves

– Barrier valves

– Suppressant barriers

– Material chokes

– Rotary valves

Classification of hazardous areas

Places where explosive atmospheres may occur are classed in terms of zones on the basis of the frequency and duration of the occurrence of the explosive atmosphere.

The extent of the organisational and protection measures to be taken is determined by this classification.

Classification of hazardous areas

Gases

Zone 0 Explosive atmosphere is present continuously or long periods or frequently,

Zone 1 Explosive atmosphere is likely to occur in normal operation occasionally

Zone 2 Explosive atmosphere not likely to occur in normal operation, if it does occur, will persist for a short time only.

Classification of hazardous areas

Dusts

Zone 20 Combustible dust cloud is present continuously or long periods or frequently

Zone 21 Combustible dust cloud is likely to occur in normal operation occasionally

Zone 22 Combustible dust cloud not likely to occur in normal operation, if it does occur, will persist for a short time only.

Note: layers and deposits must be considered as any other source which can form an explosive atmosphere

Hazardous area sign

The warning sign for places where explosive atmospheres occur:

Criteria for selection of equipment & systems

Equipment and systems must meet the requirements of Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996. (ATEX 100a Directive).

The equipment must be suitable for gases or dusts as appropriate:

In Zone 0/20 Category 1 equipmentIn zone 1/21 Category 1 or 2 equipmentIn zone 2/22 Category 1, 2 or 3 equipment

Accidents, incidents and emergencies

Appropriate emergency arrangements are required to safeguard people on the premises.

• Evacuation procedures• First Aid cover• Safety drills• Visual/audible alarms• Escape facilities• Measures to control or contain an incident• Information available to employees and emergency

services

Interface with other legislation

Provision of emergency arrangements should also take into account other legislation such as:

• COMAH

• COSHH

• Regulatory Reform (Fire safety) Order 2005.

European Harmonised Standards

In support of this legislation there are a large number of European Standards being developed by CEN in the field of explosion prevention and protection.

These include:• Test methods for determining the

flammability characteristics of substances

• Equipment for use in potentially explosive atmospheres

• Devices and systems for explosion prevention and protection

Summary of key points

• Risk assessment required.

• Hazardous area zoning required.

• Equipment chosen must be suitable for the zone.

• Signs placed on entry to zoned areas.

• Training and information.

Thank You

Steve Manchester CEng MIFireEDirector, Fire Safety Group

BRE Global, Bucknalls Lane, Watford, Hertfordshire, WD25 9XX

Tel +44 (0) 1923 664944

E steven.manchester@bre.co.uk

W www.bre.co.uk