[VAXman(Admin)]

Originally Posted by Rick and Roll

7. Cell phones may or may not be a hazard in that setting. however, they CAN interfere with critical care equipment. But the signs you see mainly deal with consideration. So while you may be correct that it probably won't interfere with the functions of most equipment, there is enough evidence to state that it can.

Mobile phones operating the the following frequency slots as per FCC allocation: 800MHz, 900MHz, 1.8GHz and 1.9GHz. Cell phones are limited to a maximum radiative power of 600mW and are typically much less. Jim can probably add more to this part of the discussion.

The biggest contributor to possible radio interference with medical equipment would be computers and wireless networking. The bands in use for wireless technology are 2.4GHz and, newer (802.11N), 5GHz. To put this into perspective, the frequency of the magnetron in the microwave oven is 2.45GHz. Wireless access points operate with radiative power of 100-500mW. Radiation at these frequencies is far more destructive than a cell phone. In large buildings, the FCC permits, under license, amplifiers of 1W, 3W and 5W to be used on WAPs.

That said, the EMI from these devices is moot. It is a teardrop in the ocean of the EMI emitted by a single fluorescent bulb. I've walked through many hospitals and doctor offices and I have never seen a warning that says do not turn on the lights because they can interfere with medical equipment. Ever wonder why CAT-5 and CAT-6 cable is UTP (unshielded twisted pair)? Office space fluorescent lighting emits so much EMI that it would interfere with straight (untwisted) cable. The twisting causes phase reversals all along the length of the cabling which effectively cancels inductive egress in the cable that would interfere with the signals. Even with UTP, I've had one or two sites where I've had to install STP (shielded twisted pair which comes at a higher price) to address EMI egress in the network runs. Typically, the problem was building code induce requiring me to put the network cables in existing runnels carrying other cabling which ran along side many fluorescent lighting fixtures.

See any old 'video tube' monitors in these facilities? These require the use of high voltage (in the range of 30KV) which is provided by a flyback transformer. The modern multi-sync monitor can have flyback frequencies from 30KHz to 150KHz. Even with shielding, such EMI is excessive.

Use of laptops prohibited? Complete rubbish! There is more computer electronics in the modern medical device that could interfere with itself than some laptop even sitting atop the medical device. The newer laptops are even better too. They run at much lower voltages giving them better battery life. Lower power consumption yields less power emitted as EMI. Units like my Powerbook, (all aluminium) use metal casing which doubles as the CPU's heat sink. From Maxwell's laws of electrodynamics:

divB = 0 :: {i∂/∂x + j∂/∂y + k∂/∂z} • B = 0 :: Gauss's law

These laptops shield the small GHz frequency EMI quit effectively.

These warnings, IMHO, come from mythconception and ignorance in the community.