RF PPE

A free electronic newsletter covering news and other topics for those interested in RF safety issues.

LIVE, Web-Based RF Safety Training

Home
Up
What is Needed?
Selecting Equipment
Understanding Specs
Survey Instruments
Monitoring Equipment
RF PPE

 

 

 

 

 

 

 

 

 

 

 

Contents

  1. What is RF PPE?
  2. Level of Protection, Limitations and Cautions
  3. Using RF PPE with RF Personal Monitors

What is RF PPE?

Personal monitors can tell you where you cannot go or should not remain, but what if you need to work in an area with significant RF fields? Protective garments are often a good solution to this problem. These suits can be considered Personal Protective Equipment (PPE). As with RF personal monitors, there is often confusion about RF protective garments.

Level of Protection, Limitations and Cautions

These garments provide a substantial amount of protection—10 dB minimum and often more and work above 50 MHz. But there are limitations and cautions, especially at lower frequencies, such as in the AM radio band:

bullet

Protection is limited -- Putting on an RF protective garment should not be equated with Clark Kent changing into his Superman outfit in a phone booth. The manufacturers of these garments stress that you should know the intensity of the field that you are entering. Yet, most survey instruments are not usable at these high field levels, which leaves computer modeling as the most common method. The conservative, recommended approach is to assume 10 dB of protection -- restrict your work to areas that are no higher than 1000 percent of the MPE limits.

bullet

Suits must be worn properly -- Suits should never be used without the hood above 800-900 MHz due to the potential for eye and brain damage at those frequencies. Hoods are generally not required below 400-500 MHz. At frequencies in between, the suits can be used at levels of 300-500 percent of the MPE.

It is critical that the body of the suit makes intimate contact with the special conductive socks. The importance of making good contact between the main part of the suit and the conductive socks cannot be overemphasized, especially if you intend to work at lower frequencies, such as near an AM radio station. The suits need to have a path to ground to work properly. If you leave the socks off, you not only do not have a good path to ground, but the currents into the suit pass through your ankles. The current density in the ankles can be very high due and can produce very high Specific Absorption Rates. If your ankles feel warm, something is wrong.

Other considerations.  The coverall, gloves, socks and hood can impede mobility and add to heat stress, and the hood can limit visibility.

Using RF PPE with RF Personal Monitors

RF personal monitors do not work underneath RF protective garments. Wearing a RF personal monitor under a RF protective suit appears to make sense to those that are not familiar with the personal monitors and the suits. It would seem that the monitor would simply detect what is getting through to the wearer.  Unfortunately, it is far more complicated than that.  There are two basic reasons why this does not work.

bullet

The minimum measurement distance for RF sensors is either 20 cm or 5 cm, depending on the standard.  In practice, many probes do not work with only a 5 cm (about two inches) spacing.  It is one of the reasons that the IEEE increased the distance to 20 cm.  With a personal monitor worn under an RF protective garment, the conductive fabric is normally touching the monitor and within less than half a centimeter from the sensors.  All types of abnormal reactions can occur with the sensor this close to a potential radiator (the conductive fabric can become a radiator).  Capacitive coupling can occur which usually means that the levels are overestimated but they can also short out the field.

bullet

The strong currents that can flow through the conductive fabric, and the fields that can occur on the surface, can interfere with the control electronics. Under some conditions this will cause false alarms.  However, under some conditions the monitor’s ability to function properly will be disrupted in terms of electromagnetic compatibility (EMC) and the monitor will not alarm at all, regardless of the magnitude of the RF field.

 

WARNING

This approach—wearing the monitor under the protective suit—does not work, is potentially unsafe for the wearer and would never be recommended by the manufacturer of the personal monitor.

A new high-power RF personal monitor is now available for use on the outside of RF protective garments. This combination of suit and monitor is the ideal solution to working in high-level RF fields. Just remember, if the monitor sounds an alarm at 1000 percent, it is time to back off and get the power reduced before you proceed!

[ Home ] [ Up ]

Send mail to web@rfsafetysolutions.com with questions or comments about this web site.
Copyright © 2007 RF Safety Solutions LLC
Site last modified: 2/28/2007