Lightning Risk and Hazard Analysis Measurement
Risk assessment as applied to Lightning Safety for Buildings and Facilities
first was conceived in 1993 at Kennedy Space Center by the US Air Force,
45th Space Wing for military launches at Space Launch Complex (SLC) 41
(1). Subsequently, the concept has been applied extensively to other SLC
areas. This risk assessment process is a tool for establishing priorities
to upgrade operational procedures and structures.
2. Elements of Risk Assessment
The essentials of risk assessment for our intent include classification
of hazards, probabilities of occurrences, and urgency of mitigation actions.
2.1. Identification of hazards. There are inherent and induced
hazards. Inherent hazards are characteristic of and intrinsic
to the type equipment. Examples are cryogenic/electrical/propulsion/pressure
systems, radioactive materials, etc. Induced hazards arise from
oversights or wrong decisions. Examples are design, production or operations
2.2. Classification of hazards. Hazards are grouped into severity
of component failure/environment/malfunction/personnel error/procedural
difficulties, etc. Class 1: Catastrophic - may cause death; Class II:
Critical - injury or damage more than $25,000; Class III: Marginal -
injury or damage less than $25,000.
2.3. Probability. Probability addresses the likelihood that
an identified hazard will cause a mishap. It is estimated as: A - Likely
to occur; B - Probably will occur; C - May occur; D - Unlikely to occur.
2.4. Risk Assessment Codes (RAC). To quantify the risks within
a hazardous operation, codes were developed using the severity classes
together with the probability estimates Sections 2.2 and 2.3, above).
RAC 1 - Imminent danger, initiate abatement procedures immediately;
RAC 2 - Serious condition exists, priority attention required; RAC 3
- 6 Non-serious condition exists, correct ASAP. The risk assessment
codes are shown in Table 1.
Table 1. Probability of Event
| I (major)
| II (significant)
| III (marginal)
3. The Hazard Analysis
The hazard analysis is an engineered safety process to control, eliminate,
identify or isolate perils, threats, and uncertainties. The process should
commence at once and be an on-going endeavor. Well-known techniques for
this include: analysis of conceptual and pre-construction drawings; engineering
and operational changes analysis; mishap investigation; readiness reviews;
walk downs and surveys; and publishing safety information such as material
safety data sheets and "lessons learned" summaries. To assist
in identifying operational hazards, the associated threats from lightning
are described in summary form:
3.l. Direct Strike. This is the most dangerous hazard, wherein
the person or structure is a direct path for lightning currents to seek
ground. The magnitude of the current determines its effects. A typical
amperage of 2OkA acting on a ground of 10 ohms creates 200,000V. A large
strike can attain l5OkA levels.
3.2. Side Strike. This hazard results from the breakup of the
direct strike when alternate parallel paths of current flow into the
ground via a person or structure. When the initial current path offers
some resistance to current flow, a potential above ground develops and
the person or structure's resistance to ground becomes the alternate
path of conduction.
3.3. Conducted Strike. This hazard occurs when lightning strikes
a conductor which in turn introduces the current into an area some distance
from the ground strike point. Unprotected connected equipment can be
damaged and personnel injured if they become an indirect path in the
completion of the ground circuit.
3.4. Structure Voltage Gradient. When current passes through
two or more structures momentary voltage differentials are created.
Poor interconnect bonding may cause a completed circuit potential difference.
The same hazard is created, for example, by a person touching an ungrounded
object while he himself is grounded - the electrical circuit is completed
through him, sometimes with fatal consequences.
3.5. Induced Effects. Lightning can induce electric field and
magnetic field coupling into structures and into wiring. Magnetic coupling
is transformer action, and the common laws for transformers prevail.
3.6. Streamer Conductor. The streamer hazard occurs when a lightning
leader influences electric behavior of objects on the earth. Even streamers
which do not become a part of the main channel can contain significant
amounts of current. Streamer current exposure can affect people and
3.7. Sequelae. These secondary effects are many. Forest and
grass fires, explosive steam conditions in masonry, trees and other
water-bearing objects, and consequences of the thunder clap startling
a person so as to drop a wrench or inadvertently throw a switch are
examples. Long term residual effects of lightning upon strike survivors
is described in Table 2 (2).
Table 2. Lightning
strike victims sequelae, frequency 25% or greater
| Memory Deficits & Loss
| Attention Deficits
| Inability to Sit Long
| Sleep Disturbance
| External Burns
| Severe Headaches
| Fear of Crowds
| Easily Fatigued
| Storm Phobia
| Stiffness in Joints
| Inability to Cope
| Irritability/Temper Loss
| General Weakness
| Unable to Work
| Loss of Strength/Weakness
| Reduced Libido
| Muscle Spasms
| Chronic Fatigue
| Coordination Problems
| Hearing Loss
| * Denotes Psychological
** Denotes Psychological or Organic No Asterisk Denotes Organic
3.8. Step Voltage/Touch Voltage. This hazard occurs as
a result of a lightning strike hitting the ground and dissipating its
energy through the ground. The ground current creates a voltage drop
across the surface of the earth, emanating from the earth entry point
radially. A person standing on the earth within several hundreds of
feet from the lightning strike point can have several hundreds of volts
generated between his feet. This hazard is identical to a person being
grounded while touch two live wires, one with each hand.
4. Performing the Hazard Analysis
All routine and non-routine work place tasks are subject to a safety
analysis. In laying out guidelines specific to each site the following
hierarchy may be useful:
4.1. Areas experiencing accidents or close calls.
4.2. Areas where changes are proposed.
4.3. Volatile/toxic/radioactive substance areas.
4.4. Process-control areas.
4.5. Electrical equipment/electrical cables & bonding & grounding.
4.6. Environmental constraint areas where moving vehicles, noise, temperatures,
and known health hazards exist.
With the use of report forms (See examples, Appendix) every activity
phase and its stages can be identified. The work subdivisions should not
be too detailed nor too gross. The purpose of the hazard analysis
is to determine and identify all dangerous operations and tasks, as well
as the risks associated with those conditions.
- Adapted from NASA Contract NAS8-30972, Oct. 1993. (STC TR-2746.)
- Englestatter, G. H., "Psychological and Neurologic Sequelae
to Lightning Strike and Electric Shock Injuries", Carolina Psychological
Health Services, Dec., 1994.