Maintaining the System C-3• Make sure that all slots and openings on the com-puter remain unobstructed, especially the fan guardon the back of the computer.• Clean the system at regular intervals to avoid anybuildup of dust and debris, which can cause a systemto overheat.• If the system is exposed to abnormally cold tempera-tures, allow a 15-minute warm-up period after it isturned on before attempting to read from or write tothe hard-disk drive.• If intermittent system failures are noticed, try reseat-ing any socketed chips, which might have becomeloose due to temperature fluctuations.HumidityHigh-humidity conditions can cause moisture migrationand penetration into the computer. This moisture cancause corrosion of internal components and degradationof properties such as electrical resistance, thermal con-ductivity, physical strength, and size. Extreme moisturebuildup inside the computer can result in electrical shorts,which can cause serious damage to the computer.Each Dell system is rated to operate at 8 to 80 percent rel-ative humidity, with a humidity gradation of 10 percentper hour. In storage, a Dell system can withstand from 8to 95 percent relative humidity.Buildings in which climate is controlled by air-conditioning in the warmer months and by heat during thecolder months usually maintain an acceptable level ofhumidity for computer equipment. However, if a system islocated in an unusually humid location, a dehumidifier canbe used to maintain the humidity within an acceptablerange.AltitudeOperating a system at high altitude (low pressure)reduces the efficiency of forced and convection coolingand can result in electrical problems related to arcing andcorona effects. This condition can also cause sealed com-ponents with internal pressure, such as electrolyticcapacitors, to fail or perform at reduced efficiency.Each Dell system is rated to operate at altitudes from -16to 3048 meters (m) (-50 to 10,000 feet [ft]) and can bestored at altitudes of -16 to 10,600 m (-50 to 35,000 ft).Dust and ParticlesA clean operating environment can greatly reduce thenegative effects of dust and other particles, which act asinsulators and interfere with the operation of a system’smechanical components. Also, in addition to regularcleaning, you should follow these guidelines to deter con-tamination of the computer equipment:• Do not permit smoking anywhere near the system.• Do not permit food or drink near the system.• Use dust covers when the system is not in use.• Keep all diskettes in a closed diskette box when notin use.• Close windows and outside doors to keep out air-borne particles.CorrosionThe oil from a person’s fingers or prolonged exposure tohigh temperature or humidity can corrode the gold-platededge connectors and pin connectors on various devices inthe computer. This corrosion on computer connectors is agradual process that can eventually lead to intermittentfailures of electrical circuits.To prevent corrosion, you should avoid touching contactson cable connectors. Protecting the system from corro-sive elements is especially important in moist and saltyenvironments, which tend to promote corrosion. Also, asa further deterrent to corrosion, the system should not beused in extreme temperatures, as explained in “Tempera-ture” discussed earlier in this appendix.Electromagnetic and Radio FrequencyInterferenceElectromagnetic interference (EMI) and radio frequencyinterference (RFI) from a computer can adversely affectdevices such as radio and television (TV) receivers oper-ating near the computer. Radio frequencies emanatingfrom a computer system can also interfere with cordlessand low-power telephones. Conversely, RFI from