~ National Lightning Safety Institute ~

Section 5.1.4

1. Overview

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 errors.

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

SEVERITY OF EVENT	(expected) A	(probable) B	(possible) C	(unlikely) D
I (major)	1	2	4	7
II (significant)	3	5	8	10
III (marginal)	6	9	11	12

 

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 sensitive electronics.

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	52% **	Depression	32% *
Attention Deficits	41% **	Inability to Sit Long	32%
Sleep Disturbance	44% *	External Burns	32%
Numbness/Parathesias	36% **	Severe Headaches	32% **
Dizziness	38% *	Fear of Crowds	29% *
Easily Fatigued	37% *	Storm Phobia	29% *
Stiffness in Joints	35%	Inability to Cope	29% *
Irritability/Temper Loss	34% *	General Weakness	29% **
Photophobia	34%	Unable to Work	29% **
Loss of Strength/Weakness	34% **	Reduced Libido	26% *
Muscle Spasms	34%	Confusion	25% **
Chronic Fatigue	32% *	Coordination Problems	28% **
Hearing Loss	25%
* 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.

5. Conclusion

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.

References:

1. Adapted from NASA Contract NAS8-30972, Oct. 1993. (STC TR-2746.)
2. Englestatter, G. H., "Psychological and Neurologic Sequelae to Lightning Strike and Electric Shock Injuries", Carolina Psychological Health Services, Dec., 1994.