Farmers Review Africa Sept/Oct 2018 FRA - September - October 2018 digital 5 | Page 21

requires a different set of solutions to mitigate fire risk and potential damage. Having completed the rational design and installation for these clients, ASP Fire also had to meet the challenge of installation in existing, functioning structures. “This raises issues of timing and cost,” Van Niekerk stresses. “We can’t always work safely in an operational facility, so certain areas need to be shut down for one month a year, when we can physically undertake the installation. This is usually in March or April, after the harvest and processing of around 50 t to 100 t of seed a day.” Working with clients to determine the safest and most cost-effective timing means finding that unique window of opportunity where the plant can be easily and cost-effectively shut down for maintenance and the installation of fire-suppression systems. Fires in solvent-extraction plants can be managed by means of ventilation, where the concentration of flammable vapours is never allowed to reach the point of combustibility. This requires forcing air into the environment to prevent build-up of flammable vapours below hexane’s lower explosive limit (LEL), as concentrations under the LEL are too lean to burn. In an open structure, there is no vapour build-up, as this is vented to atmosphere. In an enclosed structure, however, solvent vapours are heavier than air, and can accumulate on the ground, building up to the LEL. All that is required for a potential catastrophe is an ignition source. To reduce this risk, ASP Fire uses flammable-vapour detection systems, flame-detection systems and sprinklers, noting that entry is difficult in solvent plants, and also that these are largely automated, which means the risk to human lives is greatly reduced. “The key risk is a hexane leak and resultant miscella, which is the volatile mix of the oil and solvent,” van Niekerk points out. To protect equipment, high-velocity foam-spray systems are installed. The steel structure itself is protected by a foam-sprinkler system. If there is a spill from a ruptured vessel that starts to burn a layer of the spillage on the floor, this can then be enveloped in foam. All of these risk-mitigation systems from ASP Fire comply with the strict NFPA 36 standard for solvent extraction plants, which provides stringent guidelines for fire suppression and aversion. Compliance is vital for saving lives, reducing the costs of fire damage and protecting equipment and buildings from major damage. Van Niekerk points out that one of To protect equipment, high-velocity foam-spray systems are installed.The steel structure itself is protected by a foam-sprinkler system. the biggest risks in industries that use solvents such as hexane is the so-called BLEVE phenomenon, an acronym for Boiling Expanding Liquid Vapour Explosion. A hexane tanker could be up to 42 m3 in size, so an incident such as brake failure can quickly turn into a tanker fire. “These travelling tankers usually carry dry chemical powder extinguishers, but these are ineffective in putting out tyre fires. Here the biggest concern is the vessel itself starting to heat up. The danger is that the liquid reaches the point where it’s below the level of the fire, effectively creating super-heated gas,” van Niekerk elaborates. The vent on the tanker doesn’t allow for sufficiently fast ventilation, which means it heats up quicker than it is able to evaporate. The tanker then experiences a mechanical rupture, and a resultant expanding vapour cloud that ignites. The ensuing fireball is calculated to be 450 times the size of the liquid, which means that a 45 m3 tanker equates to a 250 m fireball, and massive heat radiation as a result. “One of the models we created shows that the lethal radius is 360 m from the tanker.Anything closer, and fatalities result. Even further out, September - October 2018 | 19