APPENDIX C: Control of Mitigation Measures

CONTROL OF MITIGATION MEASURES

Introduction

The following provides guidance on the key areas employers need to address in order to meet the requirements of DSEAR and covers the need to identify the hazards arising from the dangerous substance and put in place adequate ventilation, ignition controls and separation measures to control risks.

Ignition

As part of the risk assessment process employers must consider risks caused by the release of a dangerous substance in to the working environment and identify all possible sources of ignition which have the potential to cause a fire or an explosion where dangerous substances are present.

Once identified the employer must introduce measures to prevent or control the ignition sources and also ensure the risks from both intentional and unintentional sources of ignition are controlled.  Example of potential ignition sources include:

• heat energy, e.g. hot surfaces, smoking, hot work
• electrical energy, e.g. lamps, earth faults, lightning strike
• mechanical energy, e.g. friction, impact, grinding
• chemical energy, e.g. exothermic reaction, self-heating

Employers should identify where explosive atmospheres may form by classifying the hazardous areas or places into hazardous zones depending on the circumstances.

In the classified areas measures must be introduced to avoid ignition sources occurring or being brought in to the areas and will include:

• selecting and installing appropriate electrical and non-electrical equipment that is safe for use in a hazardous area
• implementing inspection, testing, cleaning and maintenance regimes for equipment
• ensuring portable or mobile equipment is suitably protected or used under safe conditions e.g. permit to work system
• prohibiting smoking or other open flames
• preventing the occurrences of static discharge
• ensuring heating systems installed cannot act as a source of ignition
• preventing accumulation of waste materials and deposits
• avoiding incompatible materials

Separation

The employer will ensure, so far as is reasonably practicable, that:

• dangerous substances can not be affected by fires in the locality
• sufficient distance is kept between potential ignition sources and any escaping gas or vapour
• a fire involving the dangerous substance does not prevent or hinder escape of personnel
• emergency services have safe access for fire-fighting or rescuing personnel
• the minimum number of people are exposed to any potential explosion

In determining what is adequate separation, employers should take into account the following:

• Properties of the dangerous substance
• Information provided by the supplier
• Quantities being stored or used
• Method of storage
• Type of activities and operations
• Design standards for the installation
• Activities on adjacent premises
• Location of the facility storing or handling the dangerous substance in relation to other features, e.g. occupied buildings, heat sources etc.

• Foreseeable incidents and emergencies
• Structures or natural features that could hinder ventilation and prolong the time, or extend the distance, that any escape of a dangerous substance could remain flammable

Where the distance required for adequate separation cannot be achieved, physical barriers of fire-resisting structure should be provided with the objective being to be capable of maintaining adequate fire protection to allow sufficient time for evacuation and emergency procedures to be implemented.

The structures required to perform as a physical barrier of fire resisting structure must comply with the relevant fire safety performance standards for example:

• Fire walls should be imperforate and provide a minimum of 30 minutes fire resistance
• Where a fire wall separates the dangerous substance from personnel the wall should provide a minimum 60 minutes fire resistance
• Any door in a fire resisting physical barriers should be self -closing and sufficiently robust to keep its integrity by any foreseeable damaging event

Ventilation

The employer should provide adequate ventilation to ensure releases of dangerous substance do not accumulate to a concentration that could be a hazard by keeping the average concentration during normal operation below that which could form an explosive atmosphere.  Adequate ventilation can be achieved by using natural mechanical, or dilution ventilation.

If the discharge of a dangerous substance from a ventilation system is emitted to general atmosphere then a process may have to be employed to remove the dangerous substance from the extracted air.

Where reasonably practicable storage and process areas should be located in the open air to allow natural ventilation.  If located in a building then natural ventilation should be provided where reasonable practicable on all external walls and at high levels i.e. roof ventilation openings.

Where natural ventilation cannot safely disperse dangerous substances then mechanical ventilation should be provided in the storage or process areas.  The provision of local exhaust ventilation (LEV) should reduce the extent or classification of any hazardous area where there is a release of a dangerous substance. Items such as ducting, trunking and casings should provide a minimum of 30 minutes fire resistance.

Electric motors of the LEV should not be positioned where deposits can build up on their surface and produce a fire hazard.  Fans may constitute a fire hazard if positioned in ductwork or hazardous places and will need to be suitably protected.

Where LEV systems are required they should be monitored for continuous operation by means of a flow-measuring device.

If the risk assessment indicates that the consequence or probability of ignition are particularly high, then to ensure that the accumulation of flammable mixtures are minimised as far as possible the higher standard of dilution ventilation should be used.  Dilute ventilation ensures that there are no stagnant or poorly ventilated spaces and any leak is mixed with air and diluted to a safe concentration.  The effectiveness of dilute ventilation should be verified.