Fire detection strategies based on hazard analysis in Scottish whisky distilleries
15 July 2016
The locating of illicit whisky stills in remote locations was not only to avoid the excise man - safety was a concern even back in the 1800s and is still important now. At risk are not just the building, stills and stock, but also the personnel and environment. In this article, James McNay of Micropack Engineering looks at the fire risks inherent within the distillation process and at the most effective methods for detecting distillery fires.
The Lagavulin distillery, Isle of Islay
The process of distilling whisky includes five key steps: malting, mashing, fermentation, distillation, and maturation. Each of these stages of production provides differing risks and will require appropriate levels of fire detection, tailored to the hazard the process presents. The weather should also be taken into consideration. Relatively minor distillery fires have in the past been turned into raging infernos by gale force winds.
The process of distilling whisky includes five key stages: Malting; Mashing; Fermentation; Distillation and Maturation
It is important to note that the last three stages of production lead to the creation of a hazardous and potentially explosive atmosphere. This in turn means that the standard detection technologies themselves become a spark potential hazard.
The following very briefly outlines the primary hazards present at each of the five typical processes involved in the distillation of Scottish whisky. Each of these stages of production provides its own set of risks and each requires appropriate levels of fire detection that have been tailored to the hazard that particular stage presents.
In the case of the malting and mashing stages, there is no alcohol present. The most prominent fire hazards here include dust explosions, but typical fire hazards can be countered with smoke/heat detection strategies relating to the detection of secondary fires. This is in contrast with the fermentation, maturation and particularly to the distillation stages, where the early detection of flaming fires is crucial.
In the malting phase, barley is germinated to promote the production of the sugars required to make alcohol. This is then ground down into a ‘grist’ (after peating in the kiln) which is then used in the mashing phase. Within these areas there is a risk of ‘domestic type’ fires associated with the equipment in use. A particular hazard here is the potential for dust explosion, but this is outwith the scope of this review as generally fire detection systems can do little to mitigate these events, other than protect against the spread of secondary fires. These secondary fires present similar hazards to the domestic type fire previously discussed.
During mashing, the grist is mixed with warm water that dissolves the sugars resulting in a mix known as ‘wort’. This wort is then used in the fermentation process. Fire hazards during this stage are similar in nature to those found in the malting stage.
During fermentation, the first alcohol is created in the form of an ale-style wash. This wash is then transferred into the Wash Still to create the spirit that will eventually become whisky.
The primary hazard related to this stage is the high concentration of Carbon Dioxide produced, which is generally vented straight out of the enclosed space. This can present a toxic hazard, in addition to any fire hazards present in this area. The fire hazard would generally be seen as domestic, as at this point the alcohol content is predominantly water, and therefore flaming hazards are unlikely in this area. From a life safety perspective, the potential toxicity from the CO2 and any leak or failure in the extraction system would be the primary cause for concern.
During distillation, the creation of high alcohol/flammable spirit provides a significant hazard. The Still House is also typically a very warm room during operation, meaning that any smoke (which would potentially have few visible particulates from a flaming alcohol based fire) might not reach ceiling height to activate a smoke detector through either thermal stratification or significant airflow from a ventilation and air conditioning (HVAC) system (if present).
As a result of the distillation process, the area is also classified as a hazardous area and falls under the ATEX directive and DSEAR legislation to protect against potentially explosive atmospheres - anyone who has been on a distillery tour will notice cameras are not allowed in the Still House as a result of the potential spark risk.
This is where the hazard moves from domestic to a process hazard, and therefore requires us to have an adequate fire detection system that will actively look for flaming fires, and which is also rated for hazardous environments. A fast response is pivotal to ensure any event is adequately mitigated against.
In order for a spirit to be officially classed as a whisky in Scotland, it must have been matured for at least three years. Maturation will typically take place in an oak or sherry cask, which helps to create the character of the specific whisky. The time in the cask will alter the amount of whisky salvaged at the end of maturation due to the ‘angels’ share’, the amount of alcohol that evaporates from the casks. The angels’ share, in addition to the flammable liquid within the casks, provides a significant fire hazard.
During the maturation phase, we have the storage of flammable spirits in significant quantities, coupled with an environment where robust detectors are required. The predominant hazard in these areas is the ignition of the flammable spirit, resulting in a potentially rapidly-spreading fire through the oaken casks being stored.
Historically, some fires in maturation houses have resulted in a boiling liquid expanding vapour explosion (BLEVE), which creates a significant escalation, and can be very dangerous to first responders and any other buildings and their occupants in the surrounding area. This, therefore, means a fast response fire detection system is required in this area.
There are many cases of devastating fires during the maturation phase which could have been prevented had the first responders had more time to protect the asset and mitigate the severity of the flame spread. The Still House and Bonded Warehouse represent two areas where passive detection such as traditional smoke and heat detectors can provide a delay in detection which might prove costly.
Why fire detection is required - brief case histories
Previous distillery fires can provide useful information on the hazards present, the risks involved and the efficacy of fire detection systems. The list below is by no means exhaustive.
Silver Trail Distillery Explosion, Kentucky, April 2015. An explosion resulting from an over-pressurised still caused a fire that destroyed the facility, killing one and injuring another. While the fire detection system could have done little to prevent the initial explosion (cited to have been caused by an internal plate having been tack fitted rather than fully welded, resulting in loss of integrity of the relief valve and thereby causing the still to explode), the escalations of secondary fires caused by the explosion are what the detection system would be intended to help mitigate.
Burghead Maltings Fire, Elgin, February 2015. A fire in the kiln area containing 60 tonnes of grain spread rapidly and the fire brigade required a high elevation vehicle to tackle the blaze, but were able to control it as it was caught early. This shows how effective a fast response can be in preventing significant escalation of a potential fire event and highlights the value of fast response detection devices.
Wild Turkey Bourbon Fire, Kentucky, May 2000. A warehouse fire destroyed 17,000 wooden barrels full of bourbon causing a massive financial loss for the distillery. As the whisky burned, it flowed from the warehouse and ignited trees in close proximity to the warehouse. This is an example of the impact a distillery fire can have on the surrounding environment when appropriate mitigation and containment measures are not in place. This event also caused the temporary shutdown of the nearby water treatment plant and led to the spillage of whisky into the Kentucky River which in turn caused the largest fish kill in Kentucky history.
Heaven Hill Distillery Fire, Kentucky, November 1996. Seven warehouse buildings and some 90,000 barrels of bourbon were consumed in a "river of fire", again causing a massive financial loss. One account of the fire stated: "Flames leapt hundreds of feet into the air and lit the sky throughout the night”. Witnesses reported seeing whisky barrels explode and rocket across the sky like shooting stars and a two-mile long stretch of the creek that supplied water to the distillery was set ablaze.
Cheapside Whisky Bond, Glasgow, 28th March 1960. A fire broke out in a Bonded Warehouse storing over one million gallons of whisky. The specific room in which the explosion took place contained 4.5 million litres of whisky and 140,000 litres of rum. This then resulted in the rupture of some casks, causing a significant BLEVE explosion. This in turn blasted through the walls of the store, which subsequently fell to the ground below, killing 19 fire service personnel, Britain’s worst peacetime fire services disaster.
Distilleries are typically classed as top tier COMAH sites due to the process and also the quantity of flammable fluids stored on site. Currently, under the ATEX Directive, with respect to explosive atmospheres in the workplace, brewers and distillers have a hierarchical responsibility: do not have a flammable atmosphere; if you do, do not ignite it; if you do, do not hurt anyone.
What can be used, and where
Traditional smoke/heat detectors
During the early processes in a distillery, there are credible arguments for having traditional smoke/ heat detectors. The environment lends itself to their application i.e. it is not a hazardous environment, and the fires expected there are typically domestic in nature. The primary hazard at the malting stage is that of a dust explosion from the grist/ fine particles that can ignite either within the equipment itself or the environment. In an occasion like this there is very little a fire detection system can do to counter the initial event. However, mitigation of secondary fires is still important, and with the potential for escalation in these areas being relatively low, the response times provided by conventional smoke/ heat detection systems are suitable for the reduction of risk to As Low As Reasonably Practicable (ALARP).
The main drawback of these detectors, however, is in the response when installed in applications with an environmental impact that can inhibit detection. This includes areas with high airflows or where thermal stratification occurs. High airflows can occur in the malting phase due to either HVAC or the opening of windows to allow the natural air into the malt floor in order to add character to the flavour. Thermal stratification can also occur in the mashing/ fermentation phases due to the increased heat at ceiling height during these processes.
Aspirated smoke detectors
Where a faster response is desired, but the hazard does not lend itself to the detection of flaming fires, aspirated smoke detection systems are becoming increasingly popular. These devices do not have many of the issues related to domestic smoke and heat detectors. As an example, they can nullify the effects of HVAC/naturally driven airflows that would direct the smoke/ heat away from the detector head of conventional devices. The aspirated devices can also combat against thermal stratification, which can be a problem in the mashing/ fermentation phase. This is where the heat generated from the process will rise in the room, and therefore the cool smoke from the fire may not reach the smoke detector until the fire has grown to the point it can be difficult to control. At that point, the mitigation function of the device has lost its effectiveness.
The aspirated units operate through actively drawing the air from the room into the unit itself. The sampling points are distributed by a pipe network, which means maintenance of the system can be carried out completely from the unit itself at ground level. This is irrespective of how complex or elevated the pipe network is throughout the room.
These units are more expensive than the more conventional smoke or heat detectors. However, with the added benefit of a fast response to a smouldering/ incipient fire, coupled with the ease of maintenance, aspirated smoke detectors are recommended for the malting and mashing phases of production.
CO2 point gas detectors
During the fermentation process, significant quantities of CO2 are produced and are vented to a safe area. If, however, this system fails, we have the potential for a toxic hazard. It is therefore prudent to provide a leak detection system to protect personnel against this potential toxic hazard.
It is also important to note that the application of a CO2 point gas detector can also double as a fire detector when calibrated correctly. As a typical fire will produce significant quantities of CO2, these devices will detect the CO2 produced in a fire as well as the CO2 by-product of the fermentation process, providing both a toxic and a smoke detector in one unit. This can therefore reduce cost and maintenance.
Optical flame detection
Optical based flame detectors have a number of benefits in distilleries. The first is in the response time. They can detect even a relatively small fire (40 kW radiant heat output) in 10 seconds or under, giving first responders a far greater chance of controlling the fire before any real damage is done.
Another benefit is that these devices offer a large field of view, so fewer need be installed than the standard prescriptive grid of passive smoke or heat detectors.
If optical based flame detection is selected, there are a number of different options available. The main choice is between the radiant and visual-based families, each with their own strengths and limitations. When looking at the distillation process, visual based flame detection provides many benefits that make it the technology of choice for this application.
From an operational standpoint, the reliability of these devices is typically very high. This is true even when exposed to the harshest of environments, as this technology was originally developed for application in the North Sea oil and gas industry.
Visual based flame detectors are not affected by issues that reduce the efficiency of traditional detection technologies, such as steam creating false alarms or dirt and grime from the environment creating a fault in the device. They are also inherently suitable for application within the hazardous and explosive environments found in distilleries.
Maintaining these devices is also relatively straightforward. This can be done using remote test torches that allow the operator to test the device from the ground up to eight metres away from the device.
The radiant family of detectors (either infrared or ultraviolet) can be affected by modulating radiation that is typically present within the warmer areas of a distillery. This can send these detectors into false alarm, or desensitise or blind the detector to a potential fire, depending on the unit selected. As visual based flame detection operates in the visual spectrum, that technology is not affected by these stimuli.
Steam can also blind radiant-based forms of optical flame detection, as the attenuation of radiation in water is 1000 times less within the visual region of the electromagnetic spectrum than that of the radiant region.
Another positive feature of visual flame detection lies within the device itself. Historically, due to the intense heat of distillery fires, the cause of a fire can be very difficult to determine as much of the evidence is destroyed. In fact, the causes of many distillery fires remain ‘undetermined.’ With visual flame detection, the on-board camera will provide a recording, acting as a ‘black box’ to show how the fire started and how it developed. This is subsequently recorded to the on-board SD card for post-incident review and can provide investigators with invaluable evidence.
It is clear that the hazards in whisky distilleries present a very unique set of circumstances, but each site is different and will require a personalised approach when it comes to the design and installation of a fire detection system.
In general, however, through examination of the hazards present at each of the main stages in the production of whisky, we can see that different technologies are best suited to the different areas within a distillery.
In those areas where a domestic-type fire is to be expected (malting, mashing and fermentation stages), conventional type smoke and heat detectors will likely be the primary form of detection. This is due to hazard analysis showing reduced escalation potential, coupled with the low cost of such devices.
Where the hazard may present increased escalation potential, but little likelihood of a flaming fire (for example where dust explosions are a credible hazard), certain aspirated smoke detection systems may be more beneficial. CO2 point gas detectors may also be useful in given circumstances.
Where flaming fires become credible and where the escalation potential is high (distillation and maturation stages), visual flame detection would usually be the optimal choice.
When tailored to the specific asset in question, the appropriate fire detection technology can greatly reduce the overall risk to a distillery and mitigate the consequences resulting from a fire event.
About the author
James McNay is Lead Technical Safety Consultant at Micropack Engineering. He is a Certified Functional Safety Professional and a member of the Institute of Fire Engineers and the Institute of Engineering and Technology.