Detection and DSEAR

The wide ranging Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) call for best working practice to be used to minimise risk. Doug Longstaff makes the case for infrared gas detection systems as being among the best technology available.

Repealing much of the previous legislation relating to flammable substances and dusts, DSEAR relates to risks from fire, explosion and ‘similar events’ arising from dangerous substances that are used or present in the workplace. A detailed definition is provided within the Regulations but, in broad terms, dangerous substances cover petrol, LPG, paints, varnishes, solvents and dusts which, when mixed with air, could cause an explosive atmosphere.

As dangerous substances can be found in varying degrees in most workplaces, DSEAR is likely to affect most industries. Similarly, explosive atmospheres are also fairly common and contain an accumulation of gas, mist, dust or vapour which, when mixed with air, has the potential to catch fire or explode. Although an explosion may not occur, there is still the risk that, if the atmosphere were to ignite, the rapid spread of flames or rise in pressure could cause an explosion, particularly in a confined space within plant or equipment such as vats or cylinders.

Similar in outline to the Control of Substances Hazardous to Health (COSHH) Regulations, the main requirements of DSEAR are that all employers and the self-employed must:

• Carry out a risk assessment of any work activities involving dangerous substances;
• Provide measures to eliminate or reduce risks as far as is reasonably practicable;
• Provide equipment and procedures to deal with accidents and emergencies;
• Provide information and training to employees;
• Classify places where explosive atmospheres may occur into zones, and mark the zones where necessary.

Clarifying the existing requirements to manage fire and explosion risks, which are set out in the Management of Health and Safety at Work Regulations, 1999, DSEAR also expands those requirements in a number of areas. For instance, unless a detailed assessment of the risks from fire, explosion and other events arising from dangerous substances has already been carried out under the Management Regulations, DSEAR requires a risk assessment to be carried out now.

In addition to addressing the requirements specified by DSEAR, the assessment should be reviewed regularly and further assessments should be carried out before starting any new work or before making modifications to existing plant or processes, including a different substance or formulation. The risk assessment should include the hazardous properties of the substance, the way they are used or stored, the possibility of hazardous explosive atmospheres occurring and cover all potential ignition sources.

The main aim is to ensure that the safety risks from dangerous substances are eliminated or, where this is not reasonably practicable, to take measures to control risks and to reduce the harmful effects of any fire, explosion, and so on. Substitution is the best solution but is not always possible. Where risk cannot be entirely eliminated, control and mitigation is required. Control measures include ventilation, avoiding ignition sources, and keeping incompatible substances apart.

Mitigation measures should be used to prevent fires and explosions from spreading, reduce the number of employees exposed and, in the case of process plant, provide plant and equipment that can safely contain or suppress an explosion, or vent the substance to a safe place. In addition, workplaces where explosive atmospheres may occur must be classified into zones based on their likelihood and persistence.

These areas must also be protected from sources of ignition by selecting equipment and protective systems meeting the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations, 1996. These zones should also be marked EX and be verified as being safe by a person or organisation competent in the field of explosion protection. All personnel working in these areas must be provided with appropriate personal protective equipment (PPE) and clothing that does not create a risk of electrostatic discharge igniting the explosive atmosphere.

These additional requirements come into effect at different times. Workplaces in use before July 2003 must meet the requirements by July 2006. Those that were in use before July 2003 but are modified before July 2006 must comply from the date of the modification, and those that became operational after 30 June 2003 must meet them from the date they came into use.

DSEAR states that, where possible, best working practice should be utilised. It also states that the workplace must be designed, constructed and maintained so as to reduce risk. Of particular relevance is the need to ensure that equipment and protective systems meet the following requirements:

• Where power failure can give rise to the spread of additional risk, equipment and protective systems must be able to be maintained in a safe state of operation independently of the rest of the plant;
• Means for manual override must be possible, operated by employees competent to do so, for shutting down equipment and protective systems incorporated within automatic processes, provided that the provision or use of such means does not compromise safety;
• On operation of emergency shutdown, accumulated energy must be dissipated as quickly and as safely as possible, or isolated so that it no longer constitutes a hazard;
• Necessary measures must be taken to prevent confusion between connecting devices.

Best working practice clearly points to failsafe technology which, in gas detection terms, means infrard. The Polytron 2IR point detector and open path IR gas detectors from Draeger are typical examples of this new breed of failsafe device.

The non-imaging, double-compensated infra-red sensor of the Polytron 2IR detector guarantees unrivalled signal stability and ensures no interference from environmental influences. Providing a fast, accurate response, it has a built-in library of 30 combustible gases or vapours and allows switching between the gases, at a touch of a button and without calibration. All the unit requires is one span gas such as methane, and the unit is automatically calibrated for all other 29 selectable gases.

Designed to detect a wide range of gaseous hydrocarbons, Draeger’s GD Series of open path gas detectors can be easily set up, aligned and commissioned without the need for special training or skills. Intrinsically safe and ideal for indoor use, each detector can monitor path lengths of up to 60 metres.

Once installed, aligned and zeroed, they require no further routine calibration and require only periodic checks of the optics and system alignment. The Draeger Polytron Pulsar open path detector can also be supplied for external use in arduous or hostile environments. All Draeger fixed gas detection systems carry full ATEX approval and can be used in a wide variety of applications to meet both the control and mitigation requirements of DSEAR. In addition, under the company’s Sensor Exchange programme, sensors can be changed quickly and easily to simplify maintenance procedures and to ensure continuous gas detection.

Mark Thompson, regional maintenance manager at Southern Water, comments: ‘Site surveys are essential, particularly in applications such as those at Southern Water where different sites present different potential hazards. A full risk assessment will help meet the DSEAR requirements and, at the same time, confirm the effectiveness of existing control measures. Potentially explosive atmospheres can then be continuously monitored with fixed gas detection systems. Southern Water chose IR for its failsafe properties and uses Draeger Regard controllers with Polytron 3000 and Polytron 2IR sensors in conjunction with the Sensor Exchange programme.’

Doug Longstaff is product manager with Draeger Safety Gas Detection Systems.