OHS Code Explanation Guide

Published Date: July 01, 2009
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Part 5 Confined Spaces

Section 44 Code of practice

Confined spaces have a history of being potentially dangerous places to work as hazards within them are often magnified. Limited access may be combined with poor ventilation, hazardous surroundings or energized equipment. When workers unknowingly enter oxygen deficient or toxic atmospheres, the results can be fatal.

A code of practice describes the procedures to be followed to allow workers to safely perform work in a confined space. Section 8 of the OHS Regulation requires that the procedures be in writing and available to workers. The code of practice must include as topics the subject matter of each section of this Part, as well as hot work as described in section 169. Section 13 of the OHS Regulation requires that workers affected by the code of practice be familiar with it before work in the confined space begins.

Workers should be consulted about the content of the code of practice as they often have the best understanding of the hazards involved in the work. It may also help to ask for the help of safety professionals such as industrial or occupational hygienists or engineers, as some situations may be particularly complex.

The code of practice must be maintained and periodically reviewed to ensure that its procedures are up-to-date and continue to reflect the work activities for which they were originally written. The code of practice must also identify all existing and potential confined space work locations at a work site so that workers can be made aware of unexpected hazards and reminded that special safety requirements apply.

Working in a confined space is potentially one of the most dangerous of all workplace hazards. According to the New Zealand Department of Labour, working in a confined space is 150 times more dangerous than doing the same job outside the confined space.

A worker is considered to have “entered” a confined space when the worker’s breathing zone crosses the plane of the confined space access.

Restricted and confined spaces

This edition of the OHS Code introduces the concept of a “restricted space”. As discussed below, restricted spaces and confined space share certain common characteristics. They differ however in key areas that may help employers and workers to operate more safely and efficiently. Some employers and workers may eventually come to think of restricted spaces as “non-permitted confined spaces”.

Restricted space explained

Like confined spaces, restricted spaces have a limited means of entry and exit. Entry points may not be designed for easy walk in. Other limitations include access by ladders or by stairways that provide poor access because of steep slope, narrow width or extreme length. Physical obstructions such as bulkheads, collapsed material, or machinery may impede exit. Limited means of entry and exit can make escape or rescue difficult.

A “restricted space” is an enclosed or partially enclosed space, not intended for continuous human occupancy that has a restricted, limited or impeded means of entry or exit because of its construction. It can be thought of as a work area in which the only hazard is the difficulty of getting into or out of the space. All other hazards are either non-existent or have been eliminated or controlled as required by Part 2. Restricted spaces are therefore not subject to the permitting, atmosphere testing and tending worker requirements of a confined space. Employers and workers must be mindful that a restricted space can become a confined space if conditions or work practices change. Employers who voluntarily apply relevant sections of ANSI Z117.1-2003, Safety Requirements for Confined Spaces, might refer to restricted spaces as “non-permitted confined spaces”.

Examples of a restricted space include

(a) an electrical or communication utility vault,
(b) a building crawl space,
(c) a trench with a temporary protective structure, and
(d) a deep excavation requiring ladder or lift access.

Despite being classified as a restricted space, the following requirements of Part 5 Confined Spaces, continue to apply to workers entering a restricted space:

  • a hazard assessment must be performed prior to entry – section 45;
  • workers assigned duties related to the entry must be trained to recognize hazards and how to perform their duties in a safe and healthy manner – section 46;
  • general safety requirements involving the use and availability of safety, personal protective, and emergency equipment, as well as a communication system – section 48;
  • prevention of unauthorized persons entering a restricted space – section 50;
  • protection of workers from hazards created by traffic in the area of the restricted space – section 51;
  • workers cannot enter or remain in a restricted space unless an effective rescue can be carried out – section 55;
  • a competent worker, designated by the employer, must be in communication with the worker(s) inside a restricted space – section 56; and
  • a safe means of entry and exit must be available to all workers required to work in the restricted space – section 57.

Confined space explained

As defined in section 1 of the OHS Code, a confined space is an enclosed or partially enclosed space that is not designed or intended for continuous human occupancy with a restricted, limited, or impeded means of entry or exit because of its construction and may become hazardous to a worker entering it because of

(a) an atmosphere that is or may be injurious by reason of oxygen deficiency or enrichment, flammability, explosivity, or toxicity,
(b) a condition or changing set of circumstances within the space that present a potential for injury or illness, or
(c) the potential or inherent characteristics of an activity which can produce adverse or harmful consequences within the space.

Confined spaces are not intended for continuous human occupancy. They are not sites of ongoing or regular work activity. They are usually entered only for such purposes as cleaning, inspection, maintenance, repair or construction. Figure 5.1 shows a flowchart that helps to determine if the space is a confined space or a restricted space.

Reasons for entering a confined space

Typical reasons for entering a confined space include:

(a) cleaning to remove sludge and other waste materials;
(b) inspecting process equipment;
(c) maintenance such as abrasive blasting and applying surface coatings;
(d) tapping, coating, wrapping and testing underground sewage, hydrocarbon, steam and water piping systems;
(e) installing, inspecting, repairing, and replacing, valves, piping, pumps, motors, etc. in below ground pits and vaults;
(f) checking and reading meters, gauges, dials, charts and other measuring instruments; and
(g) rescue of workers who are injured or overcome while inside the confined space.

Types of confined spaces

Most confined spaces are designed to hold substances such as liquids, gases, and loose materials, or to house equipment. Though they come in many sizes and shapes, most can be classified in one of two ways:

(1) spaces that are open-topped and have depth – examples include pits, wells, vats, hoppers, bins, degreasers, and kettles; and
(2) spaces with narrow openings – examples include pipes, tunnels, silos, utility vaults, casings, and sewers.

Confined spaces may have poor natural ventilation and contain, or have the potential to contain, an atmosphere that is unsafe. Poor ventilation can be the result of unpredictable or limited air movement, or natural air currents that could draw contaminated air into the space. While unsafe atmospheres are most commonly associated with spaces that are fully enclosed, vats, pits and vessels that are open-topped can also contain an unsafe atmosphere. In these cases, the unsafe atmosphere results from the entry of a gas that is heavier than air, the release of gas resulting from wastes at the bottom of the space being disturbed, or the presence of a layer of air above the space that prevents fresh air from moving into it.

Confined spaces can become unsafe as a result of

(1) atmospheric contamination by toxic substance (a concentration of a substance above the regulated exposure levels or otherwise known as safe levels) or flammable vapours, or oxygen deficiency (less than 19.5 percent oxygen by volume) or excess (more thatn 23.0 percent oxygen by volume);

(2) physical hazards i.e. electrical, thermal, radiological, noise, engulfment, etc.

(3) liquids, gases, or solids being introduced to the space during occupancy.

Some confined spaces become unsafe as a result of the conditions or work that is done inside them. Examples of conditions that can make a confined space unsafe are:

(a) manholes in contaminated ground e.g. near a leaking underground gasoline storage tank, into which poisonous or flammable gases can seep;

(b) manholes, pits or trenches connected to sewers, in which there can be a build-up of flammable and/or poisonous gases and/or insufficient oxygen in the air;

(c) tanks or pits containing sludges and other residues which, if disturbed, may partially fill the confined space with dangerous gases; and

(d) confined spaces that contain rotting vegetation, rusting metal work, and similar natural oxidation processes that create an oxygen-deficient atmosphere.

Some examples of confined spaces in which changing conditions or activities being done can make the space unsafe are:

(a) some painting work and the application of certain adhesives, cleaners and liquids such as paint thinners. These can produce dangerous amounts of solvent vapour, which can cause dizziness and impair judgment. Such solvents are often flammable so there is an accompanying risk of fire;

(b) welding activities may generate toxic gases or vapours;

(c) the use of gasoline or diesel engines can lead to the build-up of poisonous carbon monoxide gas. There is also a risk of fire resulting from leaks; and

(d) introduction of hot work.

In some cases a confined space can become unsafe because of the inherent characteristics of activities that may occur external to the space. Examples include:

  • the filling/emptying of an adjacent compartment/tank;
  • weather changes, such as thunderstorms i.e. a drop in barometric pressure, lightning, etc.;
  • heat of the day increasing vapourization and affecting personnel i.e. heat exhaustion; and
  • pipelines entering the confined space may contain hazardous materials.

Table 5.1 lists examples of confined spaces by industry.

Table 5.1 Examples of confined spaces by industry

Construction Industry
Caissons
Box beams
Sewers
Pits
Trenches
Excavations
Crawl Spaces

Food and Similar Products
Retorts
Tubs and kettles
Basins
Cold rooms
Ovens
Flour bins
Air scrubbers
Batch cookers
Caustic soda tanks
Clay hoppers
Conditioners
Continuous cookers
Extractors
Heated lard tanks
Heated sugar bins
Holding bins
Hydrogenators
Metal bins
Meal dryers
Mixers
Tallow tanks
Textiles
Bleaching ranges
J-boxes
Kiers
Die kettles
Bale presses
Dye becks
Sizing tanks
Steam boilers

Paper and Pulp
Chip bins
Barking drums
Rag cookers
Acid towers
Digesters
Beaters
Hydropulpers
Stock chests
Adhesive tanks
Chip silos
Furnaces
Machine chests
Mix tanks
Resin tanks
Clay mix tanks

Printing and Publishing
Ink tanks
Solvent tanks

Rubber Products
Solvent tanks
Shredders
Furnaces
Ovens
Mixers
Petroleum and Chemicals
Reactors
Storage tanks
Distillation columns
Cooling towers
Dike areas
Fire water tanks
Precipitators
Scrubbers
Crystallizers
Spray dryers

Leather Products
Dye vats
Tanning tanks
Sludge pits

Stone, Clay, Glass and Concrete Products
Kilns
Aggregate bins
Cement silos
Crushers
Dryers
Hoppers
Mills
Sand bins

Primary Metals
Blast furnaces
Cupolas
Coal bins
Coke bunkers
Annealing furnaces
Slag pits
Water treatment tanks
Submarine cars
Gas holders
Soaking pits
Acid pickling tanks
Plating tanks
Fabricated Metals
Paint dip tanks
Degreasers
Caustic cleaning tanks
Drying ovens
Shot blasting enclosures
Enclosed assemblies
Sludge tanks

Machinery
Boilers
Conveyers
Dust collectors
Tunnels

Electronic Industry
Degreasers
Gas cabinets
Plating/rinse tanks

Electric, Gas and Sanitary Services
Cable vaults
Manholes
Meter vaults
Transformer vaults
Bar screen enclosures
Chemical pits
Incinerators
Pump stations
Regulators
Sludge pits
Wet wells
Value puts
Digesters
Grease traps
Lift stations
Sewage ejectors
Storm drains

Based on similar table in: Rekus JF. Complete Confined Spaces Handbook. National Safety Council, Lewis Publishers, Ann Arbor; 1994.

For more information
Guideline for Developing a Code of Practice for Confined Space Entry

 
Safe Working in a Confined Space

 
They’re Not Designed to be Occupied!

 
Rekus JF. Complete Confined Spaces Handbook. National Safety Council, Lewis Publishers, Ann Arbor; 1994.