Posted By Jason McQueen
Morning Everyone. I have a bit of a problem that Im hoping people can help with. We have an industrial oven that we use as part of the manufacturing process (baking various food products).

It has been known on occasion for debris to accumulate within the oven as product falls from trays. Which, if allowed to build can result in a fire due to the material combusting. Fortunately this happens very rarely (once in the last five years) but it has happened and so the possibility is always there. We are currently looking at taking steps to ensure that the debris doesnt accumulate but, as always, you have to plan for worst case scenario.

The problem is that you can't actually tell if theres a fire within the oven unless you open one of the oven doors (full height stainless panels for the full legnth of the oven). And herein lies the problem.

By opening the oven door you are potentially exposing an employee to a fire but without opening the door there is no way of telling - catch 22. To date the fires we have had have been very small piles of product igniting (about the size of a football) but I suppose there is always the potential for a massive management system failure resulting in a larger fire. Obviously if you can see flames or smoke then you dont need to open the door but due to the enclosed nature of the oven, these obvious indicators arent always there.

So what can we do? The 'best' suggestion to date is to equip an operative with a full fire suit who can then open the door to inspect the oven. Might be over kill for 99% of the fires that occur but at least they would be protected should there be a major incident.

Posted By Ashley Wood
This is an area in which I specialise. Are the ovens you refer to traveling ovens or rotary type i.e DoubleD? If they are traveling ovens then the only safe way to identify a fire within the oven is to install a heat probe detection device within the extract stacks. This will only detect if there is an increase in the temperature above ambient. The problem comes when selecting the type of device to use as normal probes only go up to 275 degC. The other method is to utilise your oven over temp sensor. Either way you need a fire to activate the devices! Once you have detected the fire you then need a suitable system that will extinguish the fire. Co2 is not recommended due to the infeed and outfeed being obviously open. Water drenching is not recommended as it will buckle the belt and jam up the mechanism. The only method that works is 'high pressure water mist'. This produces a very fine fog in the oven which cools the belt uniformly and does not 'spot cool' and buckle it. It converts to steam as soon as it enters the oven and this inerts the inside of the oven to starve the fire of oxygen. Over a few minutes the fire will be suppressed and then extinguished. Your staff can the open the inspection hatches in safety. The added bonus is that once the burned debris has been raked out, the oven can be re-started and your back up and running again. Your insurer may even give you a reduction in your premium! If this is of help and you want more details and the names of suppliers of these systems please e-mail me.

Posted By Ashley Wood
Hi,

What is the maximum temperature of the oven? I would not recommend C02. My reasoning for this is that C02 works by reducing the Oxygen level to a level below that at which a fire can continue. It does not cool the burning product or the oven. Once you open the door to investigate this will allow a significant quantity of Oxygen into the oven and let the C02 out. Due to the residual heat in the oven the fire will 'flash back'. A flash back fire is a nightmare scenario as it is always larger.

Water mist will do the job better. Regarding temperature sensors. umm, this is always difficult. What is the temperature of the exhaust stack? How long is the extract duct?