EX zones during plant shutdowns: Closer attention required
Author : Yngve Malmén, Senior Scientist, VTT Technical Research Centre of Finland
14 March 2013
This paper points out current shortcomings in companies' risk management procedures during process plant shutdowns in relation to the so-called ATEX Workplace Directive 99/92/EC (Directive on minimum requirements for improving the safety and health protection of workers potentially at risk from explosive atmospheres). It also discusses some proactive measures that can be taken to minimise the risk of explosions affecting maintenance workers.
ATEX during plant shutdowns
Major chemical installations are designed to run for months without any stoppages, but even so, maintenance shutdowns are needed in order to avoid unwanted disturbances at the plants. Often used synonyms for plant shutdowns are the terms ‘plant turnaround’ and ‘plant outage’. According to our definition, a plant turnaround is the management process of a plant shutdown, the plant shutdown being the execution phase of the plant turnaround procedure. Plant outages, in turn, might be long or short, partial or complete and they do not necessarily involve any substantial maintenance work.
It is self-evident to safety professionals that safety management procedures should not only cover the normal operation period of a process plant, but also special cases such as shutdowns. At process plants special attention needs to be paid to shutdowns as – in the vast majority of cases – hazardous process chemicals remain present at the installation in storage tanks, warehouses, silos and pipelines even when the production process is not running.
VTT Technical Research Centre of Finland and its partners carried out a research project in order to compile information on how risks of chemical accidents during shutdowns should be handled by companies within the Finnish process industry sector. Before this, research on shutdowns mainly focused on risks caused by contractors, while the aim of the study led by VTT was to investigate if the safety management systems of the production companies were such that they ensured the safety of contractor workers during shutdowns. The study was restricted to risks caused by process chemicals. The organisations involved and our results are presented in the Finnish language on the Internet at seisokki.vtt.fi.
A brief literature survey carried out early in the project was not able to reveal any cases where hazards to contract workers - or indeed plant operators - caused by process chemicals during process plant shutdowns were dealt with in a comprehensive way. As was to be expected, many textbooks e.g. one by Carson and Mumford (1988) and one by Lees (1996) and articles in journals (e.g. by Iliffe et al, 1999, Nimmo, 1998, and West et al, 1998) have covered some aspects of this topic, such as management of change, permits-to-work, emergency planning, and crisis management. However, no comprehensive guidance on this specific topic could be found in our literature survey. Neither did we find any articles explaining how shutdowns should be handled from the perspective of the ATEX Workplace Directive.
According to the Directive 1999/92/EC an employer must:
• Prevent the formulation of explosive atmospheres in the workplace, or, avoid the ignition of explosive atmospheres, and control the effects of explosions;
• Conduct a risk assessment to identify potential sources of release;
• Classify potentially explosive atmospheres into zones;
• Mark hazardous areas with Ex signs at every point of entry;
• Maintain an explosion protection document to include risk assessment, area classification, EX training of staff and details of the permit to work system; and
• Select ATEX compliant equipment according to intended zone.
From an ATEX perspective, the first question to answer is whether a shutdown is considered to be part of the normal operation of a plant, or not. We found that the studied companies did not regard shutdowns as constituting a change that needed to be covered by management of change procedures. Neither could we find any indications in the open literature that such procedures cover shutdowns in industry in other parts of Europe either. In reality, however, the situation at the plant during a shutdown is completely different from a normal day: processes are stopped, equipment is emptied and opened, the amount of people at the site is many times higher than normal, and many safety systems are not fully functional. In addition, the situation during a shutdown is very dynamic. New hazards are being created every hour.
Article 3 of the Directive - Prevention of and protection against explosions - reads: … the employer shall take technical and/or organisational measures appropriate to the nature of the operation, in order of priority and in accordance with the following basic principles:
• the prevention of the formation of explosive atmospheres, or where the nature of the activity does not allow that,
• the avoidance of the ignition of explosive atmospheres, and
• the mitigation of the detrimental effects of an explosion so as to ensure the health and safety of workers.
These measures shall where necessary be combined and/or supplemented with measures against the propagation of explosions and shall be reviewed regularly and, in any event, whenever significant changes occur.
As The Finnish companies saw shutdowns as being an integral part of their operations, the conclusion was that either shutdowns are indeed to be taken into account when EX zoning is carried out in the first place, or alternatively, EX zones had to be reviewed and, if needed, revised prior to a shutdown in order to reflect the temporary change in circumstances a shutdown in fact constitutes.
And a second question has to be asked: Is a build-up of an explosion atmosphere during a shutdown considered always to be an unexpected event and therefore not within the ATEX framework (but under the Major Hazards Directive), or is it in some cases a consequence of a “normal” disturbance, which should be considered? I think that both cases exist, and therefore shutdowns must be considered as stated in the ATEX Workplace Directive.
The basis for any EX zoning exercise should be a risk assessment. Article 4 - Assessment of explosion risks - of the Directive says:
1. In carrying out the obligations laid down in Articles 6(3) and 9(1) of Directive 89/391/EEC the employer shall assess the specific risks arising from explosive atmospheres, taking account at least of:
* the likelihood that explosive atmospheres will occur and their persistence,
* the likelihood that ignition sources, including electrostatic discharges, will be present and become active and effective,
* the installations, substances used, processes, and their possible interactions,
* the scale of the anticipated effects.
Explosion risks shall be assessed overall.
2. Places which are or can be connected via openings to places in which explosive atmospheres may occur shall be taken into account in assessing explosion risks.
In the companies studied, risk analyses were carried out together with the contractors and their subcontractors prior to shutdowns. These risk analyses focused on risks caused by the contractors and in many cases failed to cover risks caused by the process plant itself. Nor did we find any indication in our studies - or in the open literature - that contractors would have demanded a risk analysis or safety audit to be carried out to identify hazards in the new circumstances in which the shutdown work was to be carried out. As a result, if the operating company failed to assess the explosion risks during shutdowns in a proper way, persons carrying out shutdown work are at risk of explosions or fires, or the consequences of these, such as throw-outs or cave-ins.
In some countries, guidance given by experts states that the classification of EX zones can be based on the hours per annum that an explosive atmosphere might be present in a certain location. This approach is based on the first bullet point in Article 4. If this is the only criteria, then plant shutdowns would not need to be taken into consideration when EX zones are established, as planned shutdown periods typically only last for a few days annually. This makes the likelihood of an explosive atmosphere developing or an explosion happening during the shutdown period not very high.
Nevertheless, the automation system might not be fully functioning, the air conditioning system may temporarily have been turned off or the electricity supply may have been cut for part of the system, including gas detectors and alarms. These are all factors that increase the probability of an explosion.
The consequences of an event, on the other hand, may be much more severe during a shutdown than during normal operation as the number of persons working at the plant is typically quite high – some Finnish companies reported from 100 to 500 external maintenance workers at the plant during the busiest periods of a shutdown. The total risk of a chemical accident during a shutdown might be higher than expected at first glance. Thus, if one takes the last bullet point in Article 4 - the scale of the anticipated effects - as the starting point, the “hours/year” approach is not good enough.
Point (2) of Article 4 highlights another issue relevant during shutdowns. It states that places that are (or can be) connected via openings to places in which explosive atmospheres may occur, shall be taken into account in assessing explosion risks. During shutdowns it is not at all uncommon that openings are made in the walls, or that normally closed fire doors are kept open. Some EX zones may for these reasons be larger during a shutdown than during the normal operation of the plant.
The general obligations in Article 5 of the Directive states: To ensure the safety and health of workers, the employer shall take the necessary measures, so that:
1. where explosive atmospheres may arise in such quantities as to endanger the health and safety of workers or others, the working environment is such that work can be performed safely,
2. in working environments where explosive atmospheres may arise in such quantities as to endanger the safety and health of workers, appropriate supervision during the presence of workers is ensured in accordance with the risk assessment by the use of appropriate technical means.
Another example of situations “where explosive atmospheres may arise in such quantities as to endanger the health and safety of workers or others, the working environment is such that work can be performed safely” is the situation where the ventilation system is turned off or run at a low speed. Then calculations carried out for normal plant operating situations according to, for instance, standards like IEC 60079-10-1 “Explosive atmospheres – Part 10-1: Classification of areas – Explosive gas atmospheres” are probably no longer relevant and the explosive atmosphere might be present in places not accounted for. And indeed, maintenance workers might be working in places, which in the EX zoning exercise have not been considered to be “workplaces” at all.
Article 6 of the Directive states: Where workers from several undertakings are present at the same workplace, each employer shall be responsible for all matters coming under his control. Without prejudice to the individual responsibility of each employer as provided for in Directive 89/391/EEC, the employer responsible for the workplace in accordance with national law and/or practice shall coordinate the implementation of all the measures concerning workers' health and safety and shall state, in the Explosion Protection Document…, the aim of that coordination and the measures and procedures for implementing it.
And Article 8 stipulates that the explosion protection document should be “drawn up prior to the commencement of work and revised when the workplace, work equipment or organisation of the work undergoes significant changes, extensions or conversions.” In the Explosion Protection Documents I have seen - and indeed been involved in writing myself - shutdowns have not even been mentioned! Nor have I heard that the competent authorities have paid attention to this deficit.
Finally, Article 7 of Directive 99/92/EC states that, where necessary, places where explosive atmospheres may occur in such quantities as to endanger the health and safety of workers shall be marked with signs at their points of entry.
How was this issue dealt with in the companies studied in the Finnish project? In general, Ex signs had been put up in places based on the EX zoning drawings of each plant. The problem was that some of these signs were irrelevant during the shutdown, as no chemicals were present in the area given, while others had to be observed due to residual chemicals still being present. There was, however, no possibility for the contractors to know which Ex signs were to be observed, and which not. This caused an obvious risk that if the contractor was told that a certain Ex sign could be neglected, he or she took for granted that all Ex signs were irrelevant. Or if the plant personnel showed no respect for an Ex sign, the contractors adopted the same attitude towards all of them. The lesson from this is that Ex signs should be temporarily covered or removed whenever they are not to be followed. Also, if the shutdown means that some Ex zones are larger than normal, new Ex signs should be put up.
Procedures regarding permits to work were generally in place during shutdowns in the companies studied during our project, but in many cases lack of time hindered the person signing work permits to thoroughly check that the workplace was absolutely safe. This was especially true for potential chemical hazards, as these normally cannot be detected during a brief visual check of the workplace. The researchers also observed that the work permits written for work within EX zones mainly were those for hot work. However, several maintenance operations within EX zones were not considered to be hot work, but could still ignite an explosive atmosphere.
Based on these experiences, our research team has developed a Work Permit Form specially designed for work within EX zones. This form is available in Finnish on the Internet at seisokki.vtt.fi.
Summary of possibilities for improvement
The research team made the following shutdown safety recommendations:
• More time and resources need to be allocated for risk assessments prior to a major shutdown;
• The plant’s EHS and rescue teams should take a bigger role in the planning process;
• By better scheduling of the maintenance work, bottlenecks in connection with the writing of work permits may be removed thus allowing for a proper check on the safety of the workplace before maintenance work commences. Much of the work need not be started the first morning!;
• A management procedure should be put in place to make sure that the operators (and indeed the foremen) are fully aware of how to make the plant (or the section to be shut down) safe prior to maintenance work. This procedure should also identify how to maintain this level of safety throughout the entire shutdown and start-up periods.
Conclusions
Chemical accidents at process plants are possible not only during normal operation but during shutdown periods as well. As the number of persons present during a shutdown may be much higher that otherwise, the consequences could be that much more severe.
Systematic procedures to prevent contract workers from causing accidents have been in place for many years in the Finnish process industry sector. It seems, however, that there are gaps in the way process safety is secured during shutdowns - safety issues must be kept in mind during the whole turnaround lifecycle.
Prior to the shutdown process, equipment, pipes, valves, pumps, etc. must be emptied and cleaned in a safe and reliable way. Equipment and even entire plant areas containing chemicals or utilities must be reliably isolated from the sections to be worked on during the shutdown. The success of the isolation must be verified, for instance by measuring the concentration of the chemical in question. A procedure must be in place to assess when a piece of equipment is clean enough and ventilated enough to be worked on by the contractor. And plant management must make sure that the persons in charge of making the plant safe have the necessary skills to carry out their tasks. Finally, Ex signs and gas alarms must not be neglected.
Work permits are written and signed, but in most cases time restrictions makes it impossible to thoroughly check that no chemical hazards exist, or indeed evolve while the maintenance work is carried out.
From what we have seen, in many cases there has been too much reliance on the experience of key individuals during shutdowns and too little on safety management procedures. This needs to change if companies are to be confident they are fully carrying out their responsibilities under the EU’s Seveso II and ATEX Directives.
Disclaimer
The views expressed in this paper are the views of the author only and do not necessarily reflect the views of VTT or the companies studied in the SEISOKKI project. VTT does not guarantee the accuracy of the data included in this paper and accepts no responsibility for any consequence of their use.