Explosive atmospheres in the workplace can be caused by flammable gases, mists or vapours, or by combustible dusts. Explosions can cause loss of life and serious injuries as well as significant damage, so it is vital that appropriate regulations are adhered to both in terms of processes and equipment.
The Dangerous Substances and Explosive Atmospheres Regulations (DSEAR) of 2002 and the Explosive Atmosphere Directive (ATEX 137) set the minimum requirements for protection against risks from fire, explosions and similar events arising from dangerous substances used or present in the workplace. The legislation introduced more rigorous testing for operators, including regular and representative analysis of thermal fluids.
The DSEAR places duties on employers to eliminate or control the risks from explosive atmospheres in the workplace. In DSEAR, an explosive atmosphere is defined as a mixture of dangerous substances with air, under atmospheric conditions, commonly referred to as ambient temperatures and pressures, in the form of gases, vapours, mist or dust in which, after ignition has occurred, combustion spreads to the entire unburned mixture.
ATEX is the name commonly given to the two European Directives for controlling explosive atmospheres, Directive 99/92/EC (also known as 'ATEX 137' or the 'ATEX Workplace Directive') and Directive 94/9/EC (also known as 'ATEX 95' or the 'ATEX Equipment Directive'). In Great Britain the requirements of Directive 99/92/EC were put into effect through regulations 7 and 11 of the Dangerous Substances and Explosive Atmospheres Regulations 2002 (DSEAR).
The requirements in DSEAR apply to most workplaces where a potentially explosive atmosphere may occur. Some industry sectors and work activities are exempted because there is other legislation that fulfils the requirements. DSEAR requires employers to eliminate or control the risks from dangerous substances.
Areas classified into zones must be protected from sources of ignition. Equipment and protective systems intended to be used in zoned areas should be selected to meet the requirements of the Equipment and Protective Systems Intended for Use in Potentially Explosive Atmospheres Regulations 1996. Equipment already in use before July 2003 can continue to be used indefinitely provided a risk assessment shows it is safe to do so.
It is not just in hazardous industrials such as petrochemicals that the regulations need to be adhered to. One more common area where the regulations are vital is in the management of thermal fluids. "A timely reaction to early warnings can help you avoid replacement of costly equipment and even save lives,"
Don't spare any expense
Andy Burns, technical business manager at thermal fluid specialist Global Heat Transfer, explains. "In environments where the risks are so high, no expense should be spared to ensure legislation is respected and thorough efforts are made to keep employees and premises safe."
In a nutshell, the dangers caused by the lack of preventative maintenance are rooted in the degradation of thermal fluid. Over time, heat transfer fluid breaks down through a process called thermal cracking. The fluid's molecules are broken down into smaller particles and several types of fractions are released from this chemical reaction. The first side products of thermal cracking are light ends that have a low boiling point and are very volatile.
The second category of thermal cracking decomposition products are heavy ends, which recombine to form heavy polyaromatic molecules that usually cause fouling of the heat transfer system. As a result, carbon molecules will stick to the system internals and reduce process efficiency, unless cleaned and flushed in time.
"It is crucial to remember that thermal fluid does not go from being fit for use to needing replacement overnight," Burns adds. "There is a grey area where fluids can be managed against what specialists call the degradation curve. Degradation is steady if a system is operated properly. Only as the fluid approaches the end of its practical working life, there is a gradual curve which eventually drops off very sharply. This sudden change in the quality of thermal fluids is one of the reasons why regular and preventative maintenance is so important."
Diluting the thermal fluid by topping up is a cost effective and durable option only while the fluid is in the early part of the degradation curve. After the condition of the fluid has significantly deteriorated, dilution is no longer a viable alternative. "It would have the same effect as putting a new torch battery into a two battery torch alongside a battery that has already been used for some time," Burns says. "It wouldn't be a long term solution and would result in the system not operating at optimum capacity. That being said, the best thing to do when the thermal fluid reaches the end of its lifespan is to flush and clean the system, prior to refilling it with a fresh charge of heat transfer fluid."
Despite the clarity of existing legislation and the dangers of neglecting thermal fluid analysis, companies often fail to perform the sampling DSEAR requires and carry out irrelevant tests, including lube oil tests. These are sometimes non-applicable and don't always provide the necessary information.
Sample methodology is crucial – incorrect sampling gives inaccurate flash point results which can have very dangerous consequences. Unless the fluid samples are collected when the oil is hot and circulating, they will reveal artificially high flash point values. This incorrect sampling will lead to the conclusion that the system is safe, when in reality it might not be. Inaccurate samples can have negative consequences, including decreased energy efficiency, unmanageable flash points and a dangerous working environment with risks of explosions.
The sample also needs to be closed so that no potential atmospheric particles can contaminate it or distort the results. An open sample would also allow light ends to flash off to the atmosphere, instead of remaining in the sample, which produces unreliable readings.
Frequent sampling is crucial. DSEAR says manufacturers must show they are taking appropriate measures to mitigate health and safety.
"After the samples have been taken correctly, the interpretation of data is essential and this is where Global Heat Transfer's experience and eleven-point test takes the best-practice cake," Burns says. "As opposed to most companies, that only provide a seven point test, GHT looks in detail at key data to ensure the results completely reflect reality. The three main checks that Global Heat Transfer focuses on are carbon level and amount of insoluble particles, a closed flash point test and the acidity level (TAN)."
The Ramsbottom carbon residue test (RCR) is a method of calculating the carbon residue in a fluid. If the carbon level (heavy ends) is too high, build-ups can occur, which will reduce the efficiency of the system, make pumps work harder and result in higher running costs for the company.
An acidity level test identifies the amount of additive depletion, oxidation or acidic contamination, in a thermal fluid sample. The acid number is determined by the amount of potassium hydroxide (KOH) base required to neutralise the acid in one gram of an oil sample.
"These three main areas of testing are complemented by additional checks, including appearance, viscosity, water and ferrous content, particulate quantities and fire point testing," Burns concludes. "The data from the eleven tests forms the basis of a holistic analysis based on trend data, which results in an accurate thermal fluid evaluation. Parameters for action, caution and satisfactory levels are the key factors when conducting the result analysis."
