RE: Lightening Related Safety Tips; 10-10-07

[Guest guest]

Josh,

Here are additional sites of

English/Spanish lightening safety tips:

National Lightening Institute: http://www.lightningsafety.com/index.html

¿Está

preparado para una tormenta eléctrica? http://www.redcross.org/services/disaster/foreignmat/thundspn.html

Tip Sheet in English:

Lightning

Safety for Outdoor Workers

Safety and productivity are not mutually

compatible, so one must be chosen over the other. Easy choice: SAFETY FIRST! Lightning has visited most all outdoor

work environments. Anticipate a high-risk situation and move to a low-risk

location.

Lightning safety awareness is a priority

at every outdoor facility and operation. Education is the single most important

means to achieving lightning safety. The following steps are suggested:

1. Monitor weather conditions in the early morning hours. Local weather

forecasts -- from The Weather Channel or NOAA Weather Radio -- should be noted

24 hours prior to scheduled activities. An inexpensive portable weather radio

is recommended for obtaining timely storm data.

2. Suspension and resumption of work activities should be planned in

advance. Understanding of SAFE shelters is essential. SAFE evacuation sites

include:

§

Fully enclosed

metal vehicles with windows up

§

Substantial

buildings

§

Low ground -- seek

cover in clumps of bushes

§

Trees of uniform

height, such as a forest

3. UNSAFE SHELTER AREAS include all outdoor metal objects, like power

poles, fences and gates, high mast light poles, metal bleachers, electrical

equipment, mowing and road machinery. AVOID solitary trees. AVOID water. AVOID

open fields. AVOID high ground and caves.

4. Lightning's distance from you is easy to calculate: If you hear

thunder, the associated lightning is within audible range ... about 6-8 miles

away. The distance from Strike A to Strike B also can be 6-8 miles. Suspend

activities, allowing sufficient time to get to shelter. Of course, different

distances to safety will determine different times to suspend activities. A

good lightning safety motto is:

If you can see it (lightning), flee it; if you can hear it

(thunder), clear it.

5. If you feel your hair standing on end, and/or hear " crackling

noises, " you are in lightning's electric field. If caught outside during

close-in lightning, immediately remove metal objects (including baseball cap),

place your feet together, duck your head, and crouch down low in baseball

catcher's stance with hands on knees.

6. Wait a minimum of 30 minutes from the last observed lightning or

thunder before resuming activities. Be extra cautious during this phase as the

storm may not be over.

7. People who have been struck by lightning do not carry an electrical

charge and are safe to handle. Apply first aid immediately if you are qualified

to do so. Get emergency help promptly.

Good Lightning Shelters For Outdoor Workers

By Kithil, President &

CEO, NLSI

1. Summary

Sudden

thunderstorms may bring an urgency for outdoor workers to cease work and

quickly relocate to refuge. Several safety measures should be considered by management

and by individual workers alike, including:

Early threat

detection

Notification

of affected persons

Evacuation to

safe shelters

Re-assessment

of threat levels

Resumption of

activities

NLSI's

paper entitled " An Overview of

Lightning Detection Equipment " provides background information on

threat detection and notification. Ordinary wood buildings provided for worker

comfort, lunch breaks, or safety from rain or sun are not safe from

lightning. What constitutes a safe location and why? This paper discusses

characteristics of lightning, some behavioral aspects of it, “safe”

and “not safe” structures, and their placement on typical

properties. Some examples of suitable shelters are pictured.

2.

Characteristics of lightning

Lightning

strikes are arbitrary and random. Lightning has been recorded traveling from

cloud sources 40 miles distant to cause injuries and deaths. Average

temperatures are in the 50,000 degrees F. range. Median current levels are in

the 25kA range (10mA can stop the human heart). Some 40% of lightning is forked

with two or more ground attachment points. Thunder always accompanies

lightning: “sound and light.” Hearing thunder indicates that that lightning

was within hearing range … 6 to 8 miles normally.

3. Behavior of

lightning on struck objects

High-frequency

current flowing on a metal conductor generates an electromagnetic field. One

effect of this is to confine amperages towards the outside of it. This is called

“skin effect.” The thickness of the layer of restricted penetration

is called “skin depth.” The higher the lightning frequency, the

smaller the depth. By example, a copper wire conductor at 50 Hz has a skin

depth of about 10 mm. However, lightning events induced on similar cables have

much higher frequencies, on the order of many tens of Hz, even MHz, so in this

case the skin depth is less than 1 mm. Skin depth is proportional to the square

root of the inverse of the frequency.

People

react much differently to lightning than do metal objects. The human body,

being some 65% salt water, is a good conductor. Direct lightning strikes can

follow either internal or external pathways or both. Indirect lightning damage

mechanisms include: 1) flashover from an intended conductor (for example, a

gazebo or tree) to an unintended conductor (such as a person seeking refuge

from rain or hail); 2) step and touch voltages where a person’s hands or

feet intercept electrical differentials, which then seek to equalize via the

body; and 3) interruption of normal electrical heart beats leading to

arrhythmia.

4. Safe and

not safe structures

Knowing

the above described behavior of lightning upon, say, an automobile, it is

apparent that a fully enclosed metal vehicle is a safe shelter. Other all-metal

mobile equipment — such as airplanes, buses, vans, and construction

equipment with enclosed mostly-metal cabs — also are safe. A cautionary

note, however, will emphasize that the “outer metal shield” should

not be compromised. This means:

1) Windows need to be rolled up.

2) Person must not make any interior contact with external objects, such as

radio dials, metal door handles, two-way radio microphones, etc.

3) Person should avoid all other objects that penetrate from inside to outside.

Unsafe

vehicles include those made of fiberglass and other plastics, plus small riding

machinery or vehicles without enclosed canopies, such as motorcycles, farm

tractors, golf cars, and ATVs.

Metal

buildings are safe places. So, too, are large permanent structures made of

masonry and wood. Once again, the caveat is not to become a part of the pathway

conducting lightning. This means avoiding all electrical circuits, switches,

powered equipment, metal doors and windows, hand rails, and so on. Small

post-supported structures, such as bus stops or picnic shelters, are not safe

and cannot be made safe for people.

Metal

shipping containers (also known as Conex containers or MilVans) can be easily

modified to become cheap, effective, portable, and rapidly deployable shelters.

Used ones are OK. Double walls are better than single walls. Cut out openings

for ventilation. OSHA requires two separate doors. Install metal screening (2 x

2 inches) at all openings, along with simple awnings to help keep out rain.

Install battery-powered lights; never install any AC-powered equipment. Maybe

place some wooden benches along the walls for comfort. Inspect interiors

periodically for critters, such as bees, bugs, snakes, and so on. Containers do

not need to be grounded.

Good Shelters for Lightning Protection

Poor Shelters for Lightning Protection

5. Shelter

placement on properties

How much

time, in minutes, is required to get to safe shelter from different locations

on a property? We suggest that 3-4 minutes, even under rapid evacuation, is

adequate for reaching safety. Each site location is unique and different. Here

are some examples of decisions to be made when seeking shelter:

1) Is there a pickup truck nearby that you can get to faster than an

alternative shelter?

2) If you have a choice between a metal shelter and a plastic shelter at equivalent

distances, choose the metal shelter.

3) If the only nearby structure is locked, seek an overhanging roof, where

possible.

4) If you are caught with no shelter of any type nearby, crouch to the lowest

possible position, avoiding all nearby metal objects.

6. Conclusion

To attain

100% lightning safety is not possible. But pre-planned defenses can assure a

best attempt to achieve high levels of safety. Hear thunder? When to stop

activities? Hear more thunder? Get ready to evacuate to safe shelter. What’s

a safe place? How long to stay inside the shelter? These and other questions

must be answered well in advance of the thunderstorm evacuation emergency.

7. References

Kithil, R.

(2006). Lightning

Protection For Engineers, Louisville, CO:

National Lightning Safety Institute.

Kithil, R.

and Rakov V. (2001). " Small Shelters and Safety from Lightning, "

International Conference on Lightning and Static Electricity, Seattle, WA,

September 2001.

This NLSI

website at www.lightningsafety.com

From:

[mailto: ] On Behalf Of Josh Shepherd

Sent: Wednesday, October 10, 2007

1:12 PM

To:

Subject: RE:

[ ] Question

Everyone,

I am looking for a handout, brochure, etc. that can be given to

farmworkers that educates them about lightning safety. This could include

fact sheets about the dangers of lightning, steps to take to prevent being

struck by lightning when storms come, etc. I hope that helps.

Josh Shepherd

National

Center

For Farmworker Health

Resource

Center

Manager

(512) 312-5463

-----Original

Message-----

From:

[mailto: ] On Behalf Of Tori Booker

Sent: Wednesday, October 10,

2007 12:28 PM

Subject: RE: [ ]

Question

Josh,

Could you explain a little more?

Is someone looking for detailed materials, tips for working during storms,

etc.?? Thanks, Tori

-----Original

Message-----

From:

[mailto: ]On Behalf Of Josh Shepherd

Sent: Wednesday, October 10,

2007 12:37 PM

Subject: [ ]

Question

Hello Everyone,

Do any of you know of any lightning safety materials for

farmworkers?

Josh Shepherd

National

Center

For Farmworker Health

Resource

Center

Manager

(512) 312-5463