Maintaining Spark Detection/Extinguishment Systems
In most types of process facilities, spark detection and extinguishment is the first line of defense against fires. Fire suppression, building sprinklers and similar types of equipment minimize damage once a fire has been set off. Ideally, spark detection and extinguishment can prevent those safety measures from being called on.
Like other fire-safety systems, however, spark detection and extinguishment installations need to be maintained properly. It will be the focus of this paper to examine the basic plant level maintenance requirements of a spark detection system. The information discussed will be, I hope, a basic reminder of what your maintenance personnel are already doing within your own facilities.
System Definition
A spark detection/extinguishing system must be thought of as part of a plant's overall security and safety network. Just as a residential alarm system provides protection to a homeowner, a spark detection system provides preventative protection against potential loss of human life, production facilities, equipment and costly downtime.
Any spark system is comprised of three major elements: Control Console, Detectors and Extinguishment.
The Control Console is the "brain" of the system. It receives information, processes that event information and gives instruction on the action to be taken. A control console also monitors the entire system for certain problems and gives audible and/or visual warning if they occur.
The spark sensors are the "eyes" of the system, detecting the hazard and reporting it to the console.
To satisfy various applications, different types of sensors are used according to pneumatic system temperature, pressure and ambient light conditions. Specifically to GreCon, there are three types of detectors used: the FM 1/7 for low-temperature and -pressure dust collection, the FM 3/7 for high-temperature or -pressure systems and, lastly, the DLD 1/8 for spark detection when ambient light is present.
The extinguishment equipment is the "executioner" of the hazard.
Although water is most commonly used, other extinguishing agents such as carbon dioxide, nitrogen and steam have application as a suppression medium.
Control Console
All control consoles are comprised of various electronic components and are, therefore, subject to the problems that dirt, moisture and power fluctuations can cause.
Dirt and dust are ever present in nearly all types of factories. Console enclosures normally are built to a NEMA rating, thereby protecting the electronic components as long as the door is kept closed and the conduit properly installed. Realistically, doors are periodically opened and closed or even left open for extended periods of time. This natural accumulation of dust and dirt should be carefully blown out with dry, low-pressure air every six months or more often as the situation warrants. Operators should be instructed to keep any door closed and latched as much as possible.
Naturally, moisture in or around a control console must be avoided. Should excessive moisture accidentally get into the console, removal of power and standard drying procedures for electrical/electronic equipment should be used.
Problems can occur with the electrical power of a control console. Almost all systems operate on normal 110 V a.c. input power supply. The console incorporates a transformer to make a conversion to d.c. voltage for the console's internal logic, sensors and extinguishment. In the case of GreCon, power fluctuations greater than +10%/-15% should be corrected. Every six months, the batteries of the back-up power supply and their recharging circuit should be tested.
Regular console maintenance also includes semiannual checking of connectors and wire terminals for tightness and the absence of corrosion. A visual inspection for damage of line cards, motherboards, ribbon cables and wiring integrity should also be made at the same time.
Because a spark detection system is a type of security or protection system, any kind of trouble-shooting by plant personnel should be limited to only what is outlined in the manufacturer's manual. Corrective work or diagnosis beyond what is described in the manual should be performed by or with the help of the manufacturer's trained technician.
Sensors
Most sensor problems can be grouped into three categories. Simply stated, the sensor is either bad and does not respond as it should; it is good but alarms without actually seeing a spark; or it is operative but cannot see a spark.
First, excessive vibration and moisture are the two most common causes of true sensor failure or false alarming. Failure due to vibration is normally caused by transmitted vibration from nearby or connected operating machinery such as a fan that is out of balance. The most obvious and best solution is to eliminate or reduce the vibration. If the problem persists, isolation of the sensor area from the vibrating source may be required using a flexible duct connector.
Moisture inside the sensor, due to precipitation or condensation, can also cause either failure or false alarming. To protect against precipitation, ensure that any sensor covers are tightly fastened and that their sealing gaskets are not damaged. Additionally, make certain that wire entries into the sensor are not oriented "skyward" to allow the intrusion of moisture. At certain times of the year, temperature and humidity conditions may cause internal condensation. A desiccant tablet or pad placed inside the sensor will normally solve this problem. A reminder—desiccants only last so long so maintenance personnel will need to replace them as required.
Light leaks can be another cause of false alarming. These leaks can come from missing pipe rivets, pin holes in the pipe from wear or incomplete welds, nearby access doors, failure of a sensor mount or a number of other causes. Oftentimes, this type of false alarming will occur only at specific times of the day according to the position of the sun. The sometimes not-so-simple solution is to find it and fix it.
Lastly, if a sensors lens is obscured by material or from abrasion, it may not be able to see the spark depending on the severity of blinding. A broken or cracked lens can also cause false alarming or internal damage from material intrusion. Periodic inspection of the lens should be performed. Again, refer to the manufacturer's maintenance manual for guidance and cleaning procedures.
Sensor testing should be performed on a daily basis at the minimum. Modern spark systems can be programmed to automatically test each sensor every few hours. Periodic manual testing is also recommended to confirm the self-diagnostics. Some systems require that their sensors be calibrated to bring them back into proper operation. This procedure is best accomplished by the manufacturer's trained technician. However, it is up to the user of the equipment to ensure that the required calibration is routinely scheduled.
Frequently, fiber optic cables are used in conjunction with a sensor for high-temperature or high-pressure applications. The cable is another element that must be checked for integrity. Failure of the fiber optic's ability to conduct the infrared energy to the sensor will require replacement of the cable. The viewing end of the cable should be maintained against blinding in the same manner as a normal sensor lens.
One special problem that we see quite often is on dryer systems. Condensation within the dryer duct can cause material buildup on the inside of the duct. This buildup can vary in thickness but will cause partial or total blinding of the fiber optic cable. If your plant has this problem, close attention and maintenance must be given to correct the situation.
Normal routine testing and cleaning of a daylight sensor is the same as for other types. One additional test, however, can also be performed—testing the sensor's responsiveness under different light conditions. Modern systems have sensitivity adjustment for daylight sensors, which may be changed to fine-tune the sensor's performance for a specific application.
Should a fire actually take place within the pneumatic duct, it is mandatory that each sensor or fiber optic cable be given a complete inspection for cleanliness and proper operation before resuming production.
EXTINGUISHMENT
There are four basic components that make up the extinguishment portion of a spark system. These are the nozzle, valve, Y-strainer and freeze protection system. Of the three major elements of a spark detection/extinguishment system, it is the extinguishing equipment whose maintenance seems to be neglected the most.
Problems that can occur with the nozzle include tip abrasion or wear, dirt and mineral deposits. Excessive wear on the tip of the nozzle will cause material to build up in the orifice. This partial or total plugged condition severely affects the nozzle's extinguishing ability. Nozzles must be mechanically operative. Mineral deposits from the extinguishing water can restrict or inhibit normal function. Proper nozzle maintenance is best defined as inspection. The nozzle should be removed, inspected and replaced if necessary.
Valve problems are basically either mechanical or electrical. Mechanical problems include failure to open or close properly due to contamination or wear of the internal parts. It is recommended that damaged or worn valves be replaced-and only with that spark system's approved valve. These problems will best be discovered from daily testing of the extinguishment system. Electrical problems will normally be a short or open circuit and will give a trouble alarm at the console. The trouble must be diagnosed and appropriate corrective measures taken.
The Y-strainer, preceding the valve, protects the valve from most types of harmful contamination. The strainer screen should be flushed clean on a regular basis. The frequency will depend mainly on the cleanliness of the original water supply. At least once a year, the strainer screen should be removed, inspected and replaced if needed.
The fourth component of the extinguishment system, freeze protection, normally requires little maintenance yet cannot be ignored. The most common type of protection used is a combination of heat tape, insulation and protective metal cladding. The freeze protection system should be completely checked and inspected each year in the fall and routinely monitored throughout the winter. When valve, nozzle or Y-strainer maintenance is performed during the winter, ensure that the heat tape is reconnected and the insulation and cladding properly replaced.
By conducting daily tests of the extinguishment system, most problems will be recognized and can be corrected easily. As with the control console and sensors, always follow the manufacturer's recommended maintenance schedule.
SUMMARY
Originally I stated that a spark detection/extinguishing system is part of your security and safety network. Like GreCon, most spark detection equipment has been approved, as a system, by Factory Mutual. In order to avoid compromising or voiding this approval, it is very important to always use only original authorized replacement parts. Additionally, component repair work should be done only by the manufacturer's technician.
Maintaining a safety system that could save a life cannot be overemphasized. Just pushing test buttons from the control console is not adequate. The individual components must be regularly inspected and tested. If you do not have the manpower within your own resources, establish a service agreement with the manufacturer to have their technician do a complete job of equipment inspection and testing.
<%=company%>, 7747 SW Cirrus Dr., Beaverton, OR 97008-5968. Tel: 503-641-7731; Fax: 503-641-7508.
Edited by Nick Basta
Bob Barnum is the national sales manager for GreCon, Inc. This article is based on an updated version of a paper originally presented to the 1993 National Particleboard Association Milling and Drying Seminar.