Assessing the ignition risk of mechanical systems

Edited by the Engineeringtalk editorial team Nov 9, 2005

Richard Unthank and John Walkington of Chilworth Technology assess the implications of ATEX/DSEAR compliance.

One of the requirements for ATEX/DSEAR compliance is the completion of a Hazardous Area Classification exercise.

Companies must now satisfy themselves that both electrical and non-electrical equipment used within hazardous areas meets the requirements of ATEX/DSEAR regarding potential ignition sources.

Getting this wrong can significantly increase operating costs by necessitating equipment replacement.

Under ATEX/DSEAR, companies have formal responsibilities to design, select, install, maintain and inspect equipment to ensure that it maintains its safety performance during its operating life.

This applies not only to new equipment, but also existing equipment, prior to June 2003.

To avoid unnecessary equipment replacement Chilworth's process safety specialists have developed an effective methodology for assessing ignition risks associated with mechanical equipment used within hazardous zones.

This provides a means of justifying the continued use of equipment (if appropriate) without expensive rebuild or replacement.

As a recent example, the company was asked by a fine chemicals manufacturer, based in the North of the UK, to undertake risk assessments for mechanical equipment.

This required the identification of all possible ignition sources that would or could arise in, normal operation, expected malfunction or rare malfunction.

This was cross-referenced to the equivalent equipment category definitions for any hazardous zones using Chilworth's bespoke assessment templates.

The category ratings of the equipment in the inventory were addressed, while considering a number of factors: process chemistry; layout and operating environment; the hazards and risks associated with the operating plant itself; what fault conditions could reasonably occur in normal, expected and rare malfunctions, where fault conditions could foreseeably occur, how ignition sources could arise and if so, what mitigation measures already existed to deal with such situations? This review was carried out in conjunction with the client's engineering personnel to enable the efficient identification of equipment with inherent ignition sources and the current level of risk.

The exercise was broken down into three phases, focusing on Category 1, 2 and 3 equipment.

After the review it was possible to make recommendations for safe operation including modifications and minimal replacements as appropriate.

The identification of equipment categories within its plant allowed the company to create new or modified inspection needs within the maintenance management system.

Mechanical equipment risk assessment templates were also provided, which were devised to link the operating plant conditions to the zone classification and the level of risk associated with their equipment.

As a result of this process the company was able to demonstrate that ignition sources were adequately controlled in terms of acceptable tolerable safety limits and the consequences of an ignition were reduced to an acceptable level.

This fully documented approach provided a pragmatic risk assessment, which could be audited, in support of the company's overall explosion protection philosophy, justifying the continued use of safe equipment without the need for unnecessary and costly replacement.