2.3 Confined Spaces, Ladders, Scaffolds & Hot Work

2.3 Confined Spaces, Ladders, Scaffolds & Hot Work

Quick Answer: In a permit-required confined space the acceptable oxygen range is 19.5 percent to 23.5 percent by volume, and 1926.1204(e)(3) requires atmospheric testing in a fixed order: oxygen first, then combustible gases and vapors, then toxic gases and vapors. For portable ladders, side rails must extend at least 3 feet above the upper landing surface (1926.1053(b)(1)) and the base is set out about one-quarter of the working length - the 4:1 pitch rule (1926.1053(b)(5)(i)).

Subpart AA - Confined Spaces in Construction

Subpart AA (1926.1200 through 1926.1213) governs confined-space entry on construction sites. A confined space meets all three of these tests:

1. It is large enough and so configured that an employee can bodily enter it;
2. It has limited or restricted means for entry and exit; and
3. It is not designed for continuous employee occupancy.

It becomes a permit-required confined space (PRCS) if it has any one of four characteristics:

• Contains or has the potential to contain a hazardous atmosphere;
• Contains a material with the potential for engulfing an entrant;
• Has an internal configuration such that an entrant could be trapped or asphyxiated by inwardly converging walls, or by a floor that slopes downward and tapers to a smaller cross-section;
• Contains any other recognized serious safety or health hazard.

Plumbing spaces that almost always qualify:

Hazardous atmosphere - the numbers

An atmosphere is hazardous if any one of the following is true:

• Oxygen below 19.5 percent or above 23.5 percent by volume;
• Flammable gas, vapor, or mist in excess of 10 percent of its lower flammable limit (LFL);
• Airborne combustible dust at or above its LFL;
• Any substance in a concentration above its permissible exposure limit (PEL);
• Any other atmospheric condition that is immediately dangerous to life or health (IDLH).

Methane has an LFL of roughly 5 percent by volume, so 10 percent of the LFL is 0.5 percent by volume, about 5,000 ppm - and that, not 5 percent, is the evacuation number. Methane is lighter than air and collects at the top of a manhole. Hydrogen sulfide (H2S) is heavier than air and pools at the bottom of a wet well or septic tank. OSHA's construction PEL for H2S is 10 ppm as an 8-hour TWA (1926.55, Table 1); the general-industry limit is a 20 ppm ceiling with a 50 ppm peak for 10 minutes once per shift if no other measurable exposure occurs; NIOSH lists the IDLH at 100 ppm. Its rotten-egg odor disappears at high concentration because of olfactory paralysis, so never treat your nose as a gas detector.

Why the testing order is fixed

Test oxygen first because the catalytic-bead sensor that reads combustible gas needs oxygen to burn the sample; in an oxygen-deficient space the LEL channel reads falsely low and a lethal atmosphere looks clean. Test combustibles second, because an explosion acts faster than a toxin. Test toxics last. Reversing that order is a favorite distractor.

Roles under Subpart AA

1926.1211 requires a retrieval system whenever an authorized entrant enters a permit space, unless the retrieval equipment would increase overall risk or would not contribute to rescue. The retrieval line attaches to a chest or full-body harness at the center of the entrant's back near shoulder level, or above the entrant's head, and a mechanical device - tripod and winch - must be available to retrieve entrants from vertical type permit spaces more than 5 feet deep. If an entrant is exposed to a substance for which a Safety Data Sheet exists, that SDS must be made available to the medical facility treating the entrant.

Exam Trap: More oxygen is not safer. 23.5 percent is an upper limit, not a comfort margin. An oxygen-enriched atmosphere - created by a leaking oxygen hose in a vault, or by someone "freshening" a space with an oxygen bottle - makes clothing, grease, and hair ignite violently. Any reading above 23.5 percent or below 19.5 percent is a hazardous atmosphere, and the answer choice that says "purge the space with oxygen" is always wrong. You ventilate with clean, breathable air.

Ladders and Stairways - Subpart X

1926.1051(a) requires a stairway or ladder at every point of personnel access where there is a break in elevation of 19 inches (48 cm) or more and no ramp, runway, sloped embankment, or personnel hoist is provided. A double-cleated ladder or two or more separate ladders is required when ladders are the only means of access or exit for 25 or more employees, or when a ladder must serve simultaneous two-way traffic.

Worked example. You need to reach a roof edge 12 feet above grade to terminate a vent through the roof. The side rails must clear the landing by 3 feet, so the ladder has to be long enough to place its top support at 12 feet with 3 feet of rail above it - practically a 16-foot ladder. For the pitch, the field shortcut is one foot out for every four feet of height: 12 divided by 4 = 3 feet of base setback. The exact 4:1 calculation works on the working length L, so L squared = 12 squared + (L/4) squared, which gives L squared x (15/16) = 144, L = 12.4 ft, and the setback = 12.4 / 4 = 3.1 feet. The one-tenth-of-a-foot difference is why the shortcut is what you use both in the field and on the exam.

Scaffolds - Subpart L

Scaffold training is provided by a qualified person; erecting, moving, dismantling, or altering a scaffold is done under the supervision and direction of a competent person (1926.454). Note the two different job titles - substituting one for the other is a standard distractor.

Hot Work - Soldering, Brazing, and Torches

Subpart J (1926.350 through 1926.354) plus Subpart F (1926.150 through 1926.155) cover torch work.

The fire watch

1926.352(e) says only that additional personnel shall be assigned to guard against fire during the operation "and for a sufficient period of time after completion of the work to ensure that no possibility of fire exists," and that those personnel must be instructed on the anticipated fire hazards and on how to use the firefighting equipment provided. Part 1926 gives no number - which is precisely why the question gets written.

The NFPA 51B 35-foot rule - move or protect combustibles within 35 feet of the hot work - is a fire-code figure, not a 1926.352 figure. Under 1926.150(c)(1)(i), a fire extinguisher rated not less than 2A is required for each 3,000 square feet of protected building area or major fraction of it, and travel distance from any point to the nearest extinguisher may not exceed 100 feet.

Cylinder storage and handling (1926.350)

• (a)(1) Valve protection caps in place and secured when cylinders are transported, moved, or stored.
• (a)(9) Cylinders secured in an upright position at all times, except for short periods while actually being hoisted or carried.
• (a)(10) Oxygen cylinders in storage separated from fuel-gas cylinders and from combustible materials - especially oil or grease - by a minimum of 20 feet, or by a noncombustible barrier at least 5 feet high having a fire-resistance rating of at least one-half hour.

LP-gas on the job site (1926.153)

Storage of LP-gas within buildings is prohibited. A container in use inside a building under construction is limited to 245 pounds water capacity (nominal 100 pounds of LP-gas); where multiple heater-container units share an unpartitioned area, total water capacity is limited to 735 pounds. Temporary heaters must be at least 6 feet from any container, blower and radiant heaters may not be directed toward a container within 20 feet, and safety-relief device discharge must terminate at least 5 feet horizontally from any building opening, directed away from the building.

Ventilation and flux (1926.353)

General mechanical or local exhaust ventilation is required whenever welding, cutting, or heating is performed in a confined space; where ventilation is inadequate, airline respirators plus an outside attendant and rescue procedures are required. Paragraph (c) adds controls for metals of toxic significance: zinc, lead, cadmium, and chromium bearing or coated metals require exhaust ventilation, and cadmium, lead and mercury-coated metals require local exhaust ventilation or airline respirators, while beryllium - because of its high toxicity - requires local exhaust ventilation and airline respirators.

For a plumber this is not abstract. Older silver brazing alloys contained cadmium, which is why cadmium-free BAg alloys are now the trade standard. Acid and fluoride-bearing brazing fluxes throw an irritating fume that a tight crawlspace or a valve vault will hold, so the control is a blower moving air across the joint and out - not an open hatch and hope. And per Table E-1 in 1926.102, the eye protection that goes with this work is a shade 2 filter for soldering and a shade 3 or 4 for torch brazing.