General industry and the construction industry have a lot in common when it comes to confined space hazards: the potential for fire, explosion, chemical exposure and oxygen enrichment or deficiency. In spite of the commonalities, there are significant differences between the two, says Edward J. Willwerth, an NFPA-certified marine chemist who has taught confined space safety courses for the U.S. military, shipyards, petroleum terminals, chemical manufacturers and industrial facilities.

“The largest difference will be the expectation of routine in the general industrial setting, as opposed to the expectation of variety in the construction setting,” said Willwerth.

Those differences extend to fatality rates. In statistics analyzed by NIOSH in 19941, the U.S. construction industry had a confined space fatality rate about two and a half times that of the manufacturing industry. If the focus is on trench cave-ins, the numbers are even more lopsided. During one ten-year period studied by NIOSH2, the construction industry accounted for 77 percent of the trench cave-in deaths. How can contractors and construction companies minimize confined space risks?

Understand confined spaces

While confined space hazards are varied and numerous, all confined spaces have three things in common:

  • They are large enough to enter
  • They are not easy to enter or exit
  • They are not designed for continuous human occupancy

Confined spaces include underground vaults, tanks, storage bins, manholes, pits, silos, process vessels and pipelines. Any trench deeper than four feet meets the definition of a confined space.

Train your personnel

Donald Ellenberger, environmental hazard training director for the Center for Construction Research and Training (CCRT), said the main goal of the confined spaces courses he teaches “is for construction workers to be able to recognize a confined space, and to be able to determine if the entry they are instructed to make is safe.”

Beyond that, CCRT training covers:

  • Hazards
  • Air monitoring and ventilation
  • PPE and communication
  • Isolating the permit space for entry (i.e., a lockout/tagout plan)
  • Entrants, attendants and supervisors
  • Regulations
  • Retrieval and rescue

The last topic is vital, since would-be rescuers frequently become casualties themselves. In one NIOSH study2, rescuers accounted for 36 percent of the confined spaces deaths.

Trenches: Know your dirt

Most deaths in trenches are due to cave-ins. Other risks include falls, electrocution, falling loads, hazardous oxygen and incidents involving mobile equipment.

Before a trench is dug, the contractor must name a Competent Person who knows the excavation standard, is trained in soil analysis and protective systems, can identify hazards and has the authority to stop work right away. The Competent Person must inspect the trench before every shift and after anything that might increase hazards, such as rainstorms or vibrations from nearby heavy equipment.

The type of dirt in which the trench is dug is important in determining the stability of the excavation. Even material that seems stable, such as soil with a high clay content, can cave in if it has accumulated water, been previously disturbed or is subject to vibrations from heavy traffic.

Choosing the appropriate protection system for a trench depends upon the soil type and the depth of the trench. The most common protection systems are:

  • Sloping: removal of the soil to eliminate the chance of a cave-in.
  • Shoring: a lightweight, portable and easy to install system
  • Shields: intended for trenches that are more than 20 feet deep.

In addition, any trench that is more than four feet in depth must have a ladder or some other means by which workers can quickly exit the trench.


1. Bender, Thomas R., MD, MPA. Worker Deaths in Confined Spaces. NIOSH (Publication 94-103). 1994.
2. Suruda,Anthony J., Castillo, Dawn N., Helmkamp, James C., PhD and Pettit, Ted A. Epidemiology of Confined Space Related Deaths. NIOSH (Publication 94-103-b.

SIDEBAR: Regulating confined spaces in construction

“A loss of straightforward simplicity”


A confined spaces rule for the construction industry proposed by OSHA in 2007 contains four classifications of confined spaces, each with its own protection requirements and hazard controls, instead of the two types currently identified by the agency.

Chris Williams, director of safety for Associated Builders and Contractors, Inc. (ABC), said the organization commends OSHA for trying to improve workplace safety, but predicted the additional categories would create unnecessary confusion on construction sites. “Employees will have no idea whether they’re allowed to enter a confined space or what PPE to use when they do enter it.”

In a 2008 public hearing on the proposed rule, Certified Safety Professional Gary Lopez of Florida-based Ranger Construction Industries said the four-tiered classification system “deviates from the widely understood, widely adopted two-tiered approach that identifies a space as either requiring or not requiring a permit.” Lopez added that the approach “is so important to the process of managing confined space risks and the way we teach employers and workers to be aware of those risks that we fear greatly the loss of its straightforward simplicity.”