Pressure Hazards and Confined Spaces-Chapter 18 Final.pdf

Pressure Hazards and Confined Spaces-Chapter 18 Final.pdf

1. Pressure Hazards and
Confined Spaces
Chapter 18

2. Agenda
•Definition of Pressure
•Boyles Law & Dalton's law of partial pressures
•Sources of pressure hazards in the body
•Boilers and Pressure Hazards
•High-temperature water (HTW) hazards
•Define and know hazards of Unfired Pressure Vessels
•Diagram of a typical pressure vessel showing potential
points for leakage or rupture.

3. Agenda Continued
•Know examples of Pressure Vessels used in Industry and types of testing used.
•Define a Confined Space and know Hazards
•Define LFL & UFL
•The range between the LFL and UFL is the
explosive/flammable range.
•To ensure a confined space is safe, you need to know
questions that should be asked and answered in the
affirmative before allowing entry.
•Ventilation of a confined space.

4. Pressure Hazards Defined
•Pressure is defined as the force exerted against an
opposing fluid or thrust distributed over a surface.
•Expressed in force or weight per unit of area.
•Such as pounds per square inch (psi).
•Critical injury and damage can occur with relatively
little pressure.

5. Pressure Hazards Defined
•We perceive pressure in relation to the earth's
atmosphere—at sea level, an average of 14.7 psi.
•As altitude above sea level increases, atmospheric pressure
decreases, in a nonlinear fashion.
•In human physiology studies, the typical unit of
measure is millimeters of mercury (mm Hg).

6. Pressure Hazards Defined
•Boyle's law states that the product of a given pressure
and volume is constant with a constant temperature:

7. Pressure Hazards Defined
•Air moves in & out of the lungs due to a pressure
gradient or difference in pressure.
•When atmospheric pressure is greater than pressure within
the lungs, air flows from the outside into the lungs.
•When pressure in the lungs is greater than atmospheric
pressure, air moves from the lungs to the outside.

8. Pressure Hazards Defined
•Gas exchange occurs between air in the lung alveoli
and gas in solution in blood.
•The pressure gradients causing this gas exchange are called
partial pressures.

9. Pressure Hazards Defined
•Dalton's law of partial pressures states that in a
mixture of theoretically ideal gases, the pressure
exerted by the mixture is the sum of the pressures
exerted by each component gas of the mixture:

10. Pressure Hazards Defined
•There are many sources of pressure hazards, which
result from air trapped or expanded in body cavities.
•When sinus passages are blocked, expansion of the air in
these sinuses can lead to problems.
•The same complications can occur with air trapped in the eustachian
tube of the middle ear.

11. Sources of Pressure Hazards
•Decompression sickness can result from the
decompression that accompanies a rapid rise from sea
level to at least 18,000 feet.
•Or a rapid ascent from around 132 to 66 feet underwater.

12. Sources of Pressure Hazards
•Factors influencing onset of decompression sickness:
•A history of previous decompression sickness, which increases
the probability of another attack.
•Being over 30 increases the chances of an attack.
•People in better condition have reduced chances.
•Exercise during the exposure to decompression increases the
likelihood and brings on an earlier onset of symptoms.
•Low temperature increases the probability of the sickness.
•Length of exposure of the person to the pressure is
proportionately related to the intensity of symptoms.

13. Sources of Pressure Hazards
•A reduction in partial pressure can result from reduced
available oxygen and cause hypoxia.
•Too much oxygen or oxygen, breathed under pressure
that is too high, is called hyperoxia.

14. Sources of Pressure Hazards
•The partial pressure hazard, nitrogen narcosis results
from a higher-than-normal nitrogen pressure.
•Effects may become pathogenic at depths over 200 feet, with
motor skills threatened at depths over 300 feet.
•Cognitive processes deteriorate quickly after 325 feet.

15. Boilers and Pressure Hazards
•Potential safety hazards associated with boilers and
other pressurized vessels include:
•Design, construction, or installation errors.
•Poor or insufficient training of operators; Human error.
•Mechanical breakdown or failure.

16. Boilers and Pressure Hazards
•Potential safety hazards associated with boilers and
other pressurized vessels include:
•Failure or blockage of control or safety devices.
•Insufficient or improper inspections, or preventive
maintenance
•Improper application of equipment

17. High-Temperature Water Hazards
•High-temperature water (HTW) is heated to very high
temperature—but not enough to produce steam.
•Human contact with HTW can result in extremely serious
burns, and even death.
•The two most prominent sources of hazards with HTW
are operator error and improper design.

19. Hazards of Unfired Pressure Vessels
•Unfired pressure vessels include compressed air tanks,
steam-jacketed kettles, digesters and vulcanizers, and
others that create heat internally.
•By various means rather than by external fire.

20. Hazards of Unfired Pressure Vessels
•Various means of creating internal heat include:
•Chemical action within the vessel.
•Application of some heating medium (electricity, steam, hot
oil, and so on) to the contents of the vessel.

21. Hazards of Unfired Pressure Vessels
•Potential hazards with unfired pressure:
•Hazardous interaction between the material of the vessel and
materials that will be processed in it.
•Inability of the filled vessel to carry the weight of its contents
and the corresponding internal pressure.
•Inability of the vessel to withstand the pressure introduced
into it plus pressure caused by chemical reactions that occur
during processing.
•Inability of the vessel to withstand any vacuum that may be
created accidentally or intentionally.

22. Hazards of Unfired Pressure Vessels
•The most effective preventive measure for overcoming
these potential hazards is proper design.
•Specs for design/construction of unfired pressure
vessels include:
•Working pressure & temperature range.
•Type of materials to be processed.
•Stress relief, welding or joining measures & radiography
•Beyond design -Continual inspection, proper housekeeping,
periodic testing, visual observation, use of appropriate safety
devices.

26. Cracking Hazards in Pressure
Vessels
•Pressure vessels are used in many applications to
contain many different types of substances, ranging
from water to extremely toxic chemicals.
•Leakage or rupture may occur in welded seams, bolted joints,
or at nozzles.

29. FIGURE 17–1 Diagram of a typical pressure vessel showing potential points for leakage or rupture.

30. Deaerator Vessels
•Deaerationis removing non-condensable gases,
primarily oxygen, from steam generation water.
•Deaerator vessels are used in power generation, pulp, paper &
chemical processing, and petroleum refining.

32. Amine Vessels
•The amine process removes hydrogen sulfide from
petroleum gases, such as propane and butane.
•Also used for removing carbon dioxide in some processes.
•Amine vessels are used in petroleum refineries, gas
treatment facilities, and chemical plants.
•The most common failures associated with amine vessels are
cracks in stressed or unrelieved welds.

35. Ammonia Vessels
•Vessels for the containment of ammonia are widely
used in commercial refrigeration systems and chemical
processes.
•Such vessels are typically spheres of carbon steel.
•Water & oxygen content in ammonia can cause carbon
steel to crack, particularly near welds.

36. Pulp Digester Vessels
•Pulp digestion in the manufacture of paper involves use
of a weak water solution of sodium hydroxide and
sodium sulfide in a range of 230–284 deg F.
•The most common failure in pulp digester vessels is cracking
along welded seams primarily due to caustic stress corrosion.

37. Nondestructive Pressure Vessel
Tests
•Five widely used nondestructive test methods:
•Visual examination.
•Liquid penetration test.
•Magnetic particle test.
•X-ray radiography.
•Ultrasonic test.

38. Nondestructive Pressure Vessel
Tests
•Visual, liquid penetration & magnetic particle tests can
detect only defects on, or near the surface.
•They are referred to as surface tests.
•Radiographic/ultrasonic tests can detect problems
within the material.
•They are called volumetric tests.

44. X-Ray Radiography
•An X-ray negative is made of a given portion of the
vessel, in the same way as those by physicians and
dentists.
•Irregularities such as holes, voids, or discontinuities produce a
greater exposure (darker area) on the X-ray negative.

45. Ultrasonic Test
•Similar to radar & other electromagnetic/acoustic waves
for detecting foreign objects.
•Short signals are induced into the material, and waves
reflected from discontinuities are detected by one or more
transducers.

71. FIGURE 18–3 Reduction of pressure hazards.

76. Confined Space Hazards
•A confined space is any area with limited means of
entry and exit, large enough for a person to fit into but
is not designed for occupancy.
•Vaults, vats, silos, ship/train compartments, sewers, tunnels,
etc.
•Their potential to trap toxic and explosive vapors and gases makes
confined spaces hazardous.

100. Confined Space Hazards
•The lower flammable limit LFL is the lowest
concentration of gas or vapor that can generate a flame
in the presence of a sufficient ignition source.
•The upper flammable limit (UFL) is the highest concentration
that can propagate a flame.

101. Confined Space Hazards
•The range between the LFL and UFL is the
explosive/flammable range.

102. FIGURE 18-4 Flammable/explosive range for vapors and gases.

103. Confined Space Hazards
•Take the following precautions when dealing with
confined spaces that may have a toxic environment.
•Use the most sensitive detection instrument available.
•Compare the 10% LFL for any substance in question with its
TLV, and let the TLV take precedence.

104. Confined Space Hazards
•To ensure a confined space is safe, the following
questions should be asked and answered in the
affirmative beforeallowing entry:
•Are access and exit equipment such as ladders and
steps in good working condition?
•Has the confined space been properly purged of the toxic
vapors and other toxic substances?

105. Confined Space Hazards
•To ensure a confined space is safe, the following
questions should be asked and answered in the
affirmative beforeallowing entry:
•Are lines that transport hazardous substances into or through
the confined space turned off & properly capped?
•Are all moving equipment and moving parts of equipment in
the confined space shut down and locked out?

106. Confined Space Hazards
•To ensure a confined space is safe, the following
questions should be asked and answered in the
affirmative beforeallowing entry:
•Has proper ventilation (natural or mechanical) been provided?
•Has the atmosphere inside the confined space been checked
by appropriately sensitive detection devices?

107. Confined Space Hazards
•To ensure a confined space is safe, the following
questions should be asked and answered in the
affirmative beforeallowing entry:
•Have provisions been made to monitor continually the
atmosphere inside the confined space during work?

108. Confined Space Hazards
•There are often physical hazards associated with
confined spaces.
•For example, tunnels often contain pipes that can trip an
employee or that can leak and cause a fall.
•Empty liquid or gas storage vessels may contain mechanical
equipment or pipes that must be carefully maneuvered
around, often in the dark.

109. Confined Space Permit
•Many jurisdictions mandates that an employee must
have a written permit to enter a confined space.

110. Ventilation of Confined Spaces
•Ventilation is the process of continually moving fresh air
through a space.
•Before ventilating a confined space, it should be purged,
initially clearing the space of contaminants.

111. Ventilation of Confined Spaces
•Proper ventilation, will accomplish the following:
•Dilute and replace airborne contaminants that may still be
present in the confined space.
•Ensure an adequate supply of oxygen.
•Exhaust contaminants produced by work performed in the
confined space (for example, welding, painting).

112. Ventilation and Local Exhaust
•To eliminate hazards posed by toxic contaminants such
as solvent vapors & welding fumes, exhaust the
confined space aggressively.
•Never depend solely on general ventilation to remove toxic
contaminants from the air.

113. Ventilation and Local Exhaust
•The combination of initial purging, local exhaust, and
ventilation is the ideal approach.
•If contaminant concentrations remain too high even with this
approach, employees should wear an appropriate respirator.

114. Rescue Preparation
•The time to think about getting injured employees out
of a confined space is well before they enter the space
in the first place.
•With the right planning and training, employees can be
quickly and effectively rescued from confined spaces.

115. Rescue Preparation
•Planning should answer the following questions:
•What injuries/incidents may occur in a given space?
•What types of hazards may be present in the space?
•What precautions should be taken by rescue personnel
entering the space (lifelines, hoist, respirator)?