Airborne Occupational Hazards in Sewer Systems

Amy Forsgren, Kristina Brinck

• Publisher: CRC Press
• Year: 2016
• Print ISBN: 9781498757874
• eBook ISBN: 9781315350837
• Topic: Biological Sciences
• Subtopic: Environmental Science
• Index: Biological Sciences

Sewer systems fall into the category "out of sight, out of mind" – they seldom excite interest. But when things go wrong with the air in the sewer system, they go very wrong. Consequences can be dramatic and devastating: sewer workers killed instantly by poisonous gas when they lift a sewer lid, or entire suburban blocks levelled by explosions. This book describes the atmospheric dangers commonly found in the sewer system. It provides easily-understood explanations of the science behind the hazards, combined with real-life examples of when things went dramatically wrong.

1

Introduction

1.1Why a Book on Airborne Occupational Hazards in Sewers?

Sewers are dangerous places to be, because

1. They are confined spaces
2. In these particular confined spaces, there is always the possibility of insufficient oxygen, toxic gases, explosive gases, and infectious agents

Sewer work is carried out in cramped spaces with little or no ventilation, little room for movement, and few exits or entrances.

Sewers are designed to convey a substance—human wastewater—with high organic load, undergoing constant biological decay. The breakdown of this organic matter produces a witch’s brew of toxic gases (e.g., hydrogen sulfide) and explosive gases (e.g., methane) and can consume some or all of the atmospheric oxygen. The organic matter is also extremely rich in microbes, both dead and alive. Some of them are disease-causing pathogens that can survive, even flourish, in the conditions found in the sewer system.

There are books and journal articles available on the occupational hazards of wastewater treatment plants. Consistently (and irritatingly), these publications say, “…but this particular hazard is minimal, unless you have to enter a sewer” or “This presents a hazard only in the collection system….” We decided that it was time to give center stage to the occupational hazards sewer workers face.

These hazards cannot be eliminated, since microorganisms and biological decay are an inherent part of sewage. But intelligent precautions can do a great deal to minimize the exposure to dangers. We hope to raise awareness of the hazards, so that the precautions are taken.

1.2Scope of the Work

This book provides technical information about the toxic or explosive gases, and infectious agents, most commonly found in collection systems.

The book does not provide information on legal requirements and regulations. The reader is urged to consult legal experts for questions about applicable laws and regulations. Nor does this book provide medical advice: the information used here should not be used for self-diagnosis or to determine treatments.

Many of the dangers that may arise in a collection system are very well covered elsewhere. For that reason, we have left out hazards that are common to many industries, such as

• Electrical hazards
• Slips, trips, and falls
• Machinery

We have concentrated on those hazards that are not so common in other industries and therefore are not covered as thoroughly as we would like.

1.2.1Confined Spaces

As stated at the beginning of this chapter, sewers are confined spaces. We begin accordingly by giving a brief overview of confined spaces in Chapter 2. Many readers will already have extensive knowledge of confined space hazards, precautions, and regulations; they may wish to skip Chapter 2 and go directly to Chapter 3.

1.2.2Most Common Airborne Hazards

The toxic or flammable gases upon which we have concentrated are hydrogen sulfide and methane. H₂S receives three chapters in this book; methane rates one chapter plus two case studies. These two substances are produced by the biological decay of sewage and can therefore be expected to exist in relatively large quantities in collection systems.

Carbon monoxide, carbon dioxide, oxygen deficiency, ammonia, and gasoline are also covered; but these are common industrial hazards, not at all unique to, or characteristic of, our industry. They are covered often, and well, in other safety books.

The chapters dealing with biological hazards are focused on bacterial, viral, and fungal and parasitic agents most commonly found in sewage that cause infectious diseases. Parasites, though perhaps not really an airborne hazard, are briefly touched on, simply because it seemed odd to exclude them entirely from the biological review.

1.3Some Useful Background Information

Several of the chapters in this book deal with flammable/explosive gases and make repeated reference to lower flammability limit (LFL), lower explosive limit (LEL), limiting oxygen concentration (LOC), and so on. A brief explanation is provided in this section of what the terms mean as used in this book.

Also, the North American readers will be familiar with the National Institute for Occupational Safety and Health (NIOSH), Occupational Safety and Health Administration (OSHA), American Conference of Governmental Industrial Hygienists (ACGIH), and so on; but for readers from other continents, these terms are briefly explained in Section 1.3.2.

1.3.1Explanation of LEL/UEL, LFL/UFL, and LOC

The LFL is the minimum concentration of fuel in air for combustion to occur; below this the fuel/air mixture is too “lean.” The upper flammability limit (UFL) is the maximum concentration of fuel in air for combustion to occur; above this the fuel/air mixture is too “rich.” These are also known as lower explosive limit and upper explosive limit (LEL and UEL).

The LOC* is the minimum concentration of oxygen for combustion to take place; below this amount, combustion is not possible, no matter what the fuel concentration is.

It is important to note that these properties do not define hard-and-fast boundaries between “safe” and “unsafe” conditions. They are not fundamental properties of each chemical species. Instead, they are the result of measuring particular gas mixtures in particular apparatuses using particular methods [1]. They can be expected to change with circumstance, for example, when adding more gases to the mix.

1.3.2Who’s Who and What’s What for Occupational Exposure

The ACGIH is a well-respected nongovernmental organization whose recommendations generally carry a lot of weight. The ACGIH develops and publishes guidelines called Threshold Limit Values (TLVs®) for exposure to workplace chemicals. TLVs are the airborne concentration of a substance that nearly all workers may be exposed to repeatedly without adverse health effects [2].

The ACGIH TLVs are frequently incorporated into legal regulations governing workplace chemical exposure. They may also be incorporated into industry standards issued by associations such as the National Fire Protection Association.

The NIOSH is part of the U.S. federal government (Department of Health and Human Services). NIOSH tests equipment, evaluates and approves respirators, conducts studies of workplace hazards, and proposes standards to OSHA. NIOSH scientists determine the concentration that should be regarded as immediately dangerous to life or health (IDLH concentration) and a Recommended Exposure Limit (REL).

TABLE 1.1
Comparable Terms

Terms in United States and Canada	Terms in Great Britain
PEL	WEL, workplace exposure limit (EU: OELV)
TWA	LTEL, long-term exposure limit
STEL	STEL

The European Union’s analogous body to NIOSH is the Scientific Committee on Occupational Exposure Limits (SCOEL).

OSHA is the part of the U.S. federal government (Department of Labor) that adopts and enforces health and safety standards in the United States. OSHA uses the term Permissible Exposure Limit (PEL) to define the maximum concentration of a specific chemical to which an unprotected worker may be exposed. A specific chemical may have one or more types of PEL:

• TWA: Time-weighted average, usually set for an 8-hour workday
• STEL: A 15-minute short-term exposure limit that should not be exceeded during a workday
• C: Ceiling concentration that should not be exceeded at any point during a working period

Table 1.1 shows the comparable terms used by Canada, Great Britain, and the United States for PEL, TWA, and STEL.

References

1.Crowl, D. A. (2012). Minimize the risks of flammable materials. Chemical Engineering Progress, 108(4), 28–33.

2.ACGIH. (1991). Documentation of the Threshold Limit Values and Biological Exposure Indices, 6th ed. American Conference of Governmental Industrial Hygienists: Cincinnati, OH, Vol...

Table of contents

• Cover
• Half Title
• Title Page
• Copyright Page
• Dedication
• Contents
• Foreword by Markus Holmberg
• Foreword by Vikram Nanwani
• Acknowledgments
• About the Authors
• Acronyms
• 1. Introduction
• 2. Confined Spaces
• 3. Hydrogen Sulfide, Part 1: The Macro View
• 4. Hydrogen Sulfide, Part 2: Toxicology
• 5. Biomarkers for Hydrogen Sulfide Poisoning
• 6. Methane and Natural Gas
• 7. Methane Case Study: The Abbeystead Explosion
• 8. Case Study, Natural Gas: The East Ohio Gas Co. Explosion
• 9. Other Vapors or Gases
• 10. Biological Hazards
• 11. Viral Hepatitis
• 12. Leptospirosis/Weill’s Disease
• 13. Exercises
• Index