Before you start
Objectives: learn about sources of hazard in electronic devices.
Prerequisites: no prerequisites
Key terms: current, voltage, laser, heat, fire, protection
We should never work on any device until we have powered it down and unplugged it from the wall. If we are working on a portable computer, we have to make sure the battery is out. Power that comes from the wall is Alternating Current (SC), about 115 volts at 60 cycles in USA or 220 volts at 50 cycles in EU. Also, we have to ensure that the grounding pin on a PC power plug is intact. AC can be enough to stop our heart. Power coming out of a wall can be retained even after the device is unplugged from the wall. It is retained in the device’s power supply, in capacitors. Because of that we should avoid opening the power supply since capacitors store a large charge of electricity. New power supplies constantly pull power from the socket so we have to unplug the system before we start to work on internal components. To protect components against ESD we should use anti-static wrist strap. This can also reduce the chance of accidental electrical shock, so we should ground ourselves before working with components.
Capacitors in a high voltage power supply can retain enough current, enough power, to kill us even hours after the device is unplugged from the wall. This is why a power supply in a computer is an FRU (Field Replaceable Unit). It is not a serviceable part of the computer. We should avoid servicing anything to do with high voltage, including computer power supplies. Another source of high voltage is a CRT monitor, so we should not work inside a CRT monitor. CRT monitors can store 20,000 to 30,000 volts of electricity, even when unplugged, so if we must work within a CRT, we have to discharge the high voltage first. When talking about CRT monitors, we have to mention that CRT tube in a monitor contains toxic substances, such as lead, phosphorous, cadmium, barium and mercury, so we should not try to open it or break it. The important thing to remember is not to wear ESD bracelet (anti-static wrist strap) around high voltage devices like monitors, power supplies, LCD panels, etc. If we are grounded in this case, we become the path of least resistance for current and the high voltage current will flow trough us.
Another safety consideration is thermals or heat. Any component which has a heat sink, the printing head of a dot matrix printer, or components inside a laser printer can be hot. We should allow a system to cool for minute or two before we work on it, to avoid burns.
Printers can also present a safety hazard. Laser printers use laser light that can damage our eye. They also use toner which we can inhale, so we should not locate laser printers immediately next to us. The toner is fused, or melted onto the paper by fuse rollers which can get very hot. Other printers that present a hazard are dot matrix printers. Solenoids, little coils in the print head get very hot. In general, if the component has a heat sink, or a heat spreader on it, that tells us to let the device cool down before we touch it.
DVD and CD drives write the data with laser light which can damage our eyes. Also, we should never look down the end of a fiber optic cable. Instead, we can shine the light into our hand and look for a dot.
We should always have a Class C fire extinguisher available. A Class C fire extinguisher is made for electrical fires. Fire protection is especially important when talking about server rooms. We should always keep the server room free of flammable materials. We should always have a fire extinguishers available in the server room.
Water and other liquid materials can damage computer systems. This is especially important in server rooms. To protect computers against water, we should avoid basements as our server rooms. We should also know the location of water pipes in the building, so that we can avoid putting our equipment close to pipes which can brake and leak. We can also use water resistant racks. Those racks are not water-proof, but have cabinets around the equipment which will help keep it dry.
Any component that presents a potential hazard ships with its own MSDS (Materials Safety Data Sheet) or PSDS (Product Safety Data Sheet). An MSDS explains, among other things, what to do if we come in contact with something relating to an electronic component that’s potentially dangerous to us.
We should never work on a device until we have powered it down and unplugged it from the wall. The important thing to remember is not to wear ESD bracelet around high voltage. We should allow a system to cool for minute or two before we work on it. Laser light that can damage our eye. We should always have a Class C fire extinguisher available.