{"id":987475070,"date":"2024-09-15T03:42:52","date_gmt":"2024-09-15T03:42:52","guid":{"rendered":"https:\/\/courses.asiascubainstructors.com\/lessons\/skills-and-environmetn-4-project-aware-copy\/"},"modified":"2024-09-16T12:57:10","modified_gmt":"2024-09-16T12:57:10","slug":"decompression-theory-and-rdp-1-the-haldanean-decompression-model","status":"publish","type":"lessons","link":"https:\/\/courses.asiascubainstructors.com\/de\/lessons\/decompression-theory-and-rdp-1-the-haldanean-decompression-model\/","title":{"rendered":"Restricted content"},"content":{"rendered":"

[et_pb_section fb_built=”1″ admin_label=”Classes Section” _builder_version=”4.23.1″ _module_preset=”2fe31fc0-c6cb-4cdc-be65-5cba107172ab” background_color=”RGBA(255,255,255,0)” custom_margin=”||||false|false” custom_padding=”0px||||false|false” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_row use_custom_gutter=”on” gutter_width=”1″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_color=”#4E70C9″ background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”3%|3%|3%|3%|true|true” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.22.0″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”8b1f8231-1210-4c64-bae4-d177be5c655c” text_text_color=”#FFFFFF” header_2_text_color=”#FFFFFF” header_3_text_color=”#FFFFFF” header_4_text_color=”#FFFFFF” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Decompression theory and the RDP<\/h1>\n

 <\/p>\n

1. The Haldanean Decompression Model<\/h2>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row make_equal=”on” admin_label=”Class Details Area” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”10%||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.22.0″ _module_preset=”default” custom_padding=”||||false|false” custom_padding_phone=”|5%||5%” custom_padding_last_edited=”off|desktop” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

The Haldanean Decompression Model<\/h3>\n

Almost all dive tables and dive computers are based on a Haldanean decompression model<\/strong><\/em>. This is named after John Scott Haldane who developed the first mathematical formula (model<\/strong><\/em>) for decompression sickness.
Modern decompression models are based on the same ideas.<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”3_5,2_5″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”3_5″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” custom_padding=”||5%|” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Tissue pressure<\/h3>\n

When a diver is on the surface, he is breathing air at a pressure of 1 Bar. Air has 21% oxygen and 79% nitrogen. The nitrogen exerts a partial pressure of 0.79 Bar.<\/p>\n

The human body absorbs nitrogen. As you have learned in physics, dissolved gasses can also exert pressure. The pressure of nitrogen in the diver\u2019s body, when he is breathing air on the surface, is also 0.79 Bar. The nitrogen pressure in the diver\u2019s body (tissue pressure<\/strong><\/em>) is in balance with the nitrogen pressure in the air that he is breathing.<\/p>\n

[\/et_pb_text][\/et_pb_column][et_pb_column type=”2_5″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|0px||5%” custom_padding_tablet=”” custom_padding_phone=”10%|||0px” custom_padding_last_edited=”on|phone” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_image src=”https:\/\/courses.asiascubainstructors.com\/wp-content\/uploads\/2024\/09\/PADI-IDC-theory-nitrogen.jpg” force_fullwidth=”on” align_tablet=”center” align_phone=”” align_last_edited=”on|desktop” _builder_version=”4.16″ _module_preset=”default” animation_style=”fade” animation_delay=”500ms” global_colors_info=”{}” theme_builder_area=”post_content”]   [\/et_pb_image][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”3_5,2_5″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”3_5″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” custom_padding=”||5%|” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Pressure gradient<\/h3>\n

When the diver descends to a given depth, the nitrogen pressure in his breathing air is higher than the nitrogen tissue pressure in his body, so more nitrogen dissolves into the body tissues.<\/p>\n

The difference between the dissolved nitrogen tissue pressure and the nitrogen pressure in the breathing air is called the pressure gradient<\/strong><\/em>. Tissue pressure and pressure gradient are normally expressed as partial pressure nitrogen, PPN2 (Bar).<\/p>\n

With enough time, the nitrogen tissue pressure again will be the same as the nitrogen pressure in his breathing air. No more nitrogen will be dissolved in his body, as long as the diver stays on the same depth. This is called saturation<\/strong><\/em>.<\/p>\n

[\/et_pb_text][\/et_pb_column][et_pb_column type=”2_5″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|0px||5%” custom_padding_tablet=”” custom_padding_phone=”10%|||0px” custom_padding_last_edited=”on|phone” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_image src=”https:\/\/courses.asiascubainstructors.com\/wp-content\/uploads\/2024\/09\/PADI-IDC-theory-saturation.jpg” alt=”PADI-IDC-theory-saturation” title_text=”PADI-IDC-theory-saturation” force_fullwidth=”on” align_tablet=”center” align_phone=”” align_last_edited=”on|desktop” _builder_version=”4.22.0″ _module_preset=”default” animation_style=”fade” animation_delay=”500ms” global_colors_info=”{}” theme_builder_area=”post_content”]   [\/et_pb_image][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,2_3″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”1_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|||0px” custom_padding_tablet=”” custom_padding_phone=”|||0px” custom_padding_last_edited=”on|desktop” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_image src=”https:\/\/courses.asiascubainstructors.com\/wp-content\/uploads\/2024\/09\/PADI-IDC-theory-supersaturation.jpg” alt=”PADI-IDC-theory-supersaturation” title_text=”PADI-IDC-theory-supersaturation” force_fullwidth=”on” align_tablet=”center” align_phone=”” align_last_edited=”on|desktop” _builder_version=”4.22.0″ _module_preset=”default” animation_style=”fade” animation_delay=”500ms” global_colors_info=”{}” theme_builder_area=”post_content”]   [\/et_pb_image][\/et_pb_column][et_pb_column type=”2_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Supersaturation<\/h3>\n

When the diver ascends, the nitrogen tissue pressure in the body becomes higher than the nitrogen pressure in his breathing air, causing the tissues to release nitrogen.\u00a0This is called supersaturation<\/strong><\/em>. The tissues will release nitrogen until again, a balance is reached.<\/p>\n

After every dive, the diver will be supersaturated. This does not necessarily cause decompression sickness. However, if the pressure gradient exceeds acceptable limits bubbles may form and cause decompression sickness.
These limits are dictated by the decompression model from the RDP table or computer and are called the M-values<\/strong><\/em>.<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,2_3″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”1_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|||0px” custom_padding_tablet=”” custom_padding_phone=”|||0px” custom_padding_last_edited=”on|desktop” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_image src=”https:\/\/courses.asiascubainstructors.com\/wp-content\/uploads\/2024\/09\/PADI-IDC-theory-halftime.jpg” alt=”PADI-IDC-theory-halftime” title_text=”PADI-IDC-theory-halftime” force_fullwidth=”on” align_tablet=”center” align_phone=”” align_last_edited=”on|desktop” _builder_version=”4.22.0″ _module_preset=”default” animation_style=”fade” animation_delay=”500ms” global_colors_info=”{}” theme_builder_area=”post_content”]   [\/et_pb_image][\/et_pb_column][et_pb_column type=”2_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Halftime<\/h3>\n

How quickly or slowly the pressure gradient changes is defined by the halftime<\/strong><\/em>. Halftime can be explained as the time it takes to reduce a certain value to half (in this case the pressure gradient). Halftime is used to calculate nitrogen release as well as nitrogen absorption.<\/p>\n

If the halftime is 1 hour, the pressure gradient will be reduced to 50% after 1 hour, 25% after 2 hours, 12.5% after 3 hours and so on. After 6 halftimes (1.56%) the pressure gradient is considered zero (saturated).<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,2_3″ make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”1_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”|||0px” custom_padding_tablet=”” custom_padding_phone=”|||0px” custom_padding_last_edited=”on|desktop” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_image src=”https:\/\/courses.asiascubainstructors.com\/wp-content\/uploads\/2024\/09\/PADI-IDC-theory-slow-fast-compartments.jpg” alt=”PADI-IDC-theory-slow-fast-compartments” title_text=”PADI-IDC-theory-slow-fast-compartments” force_fullwidth=”on” align_tablet=”center” align_phone=”” align_last_edited=”on|desktop” _builder_version=”4.22.0″ _module_preset=”default” animation_style=”fade” animation_delay=”500ms” global_colors_info=”{}” theme_builder_area=”post_content”]   [\/et_pb_image][\/et_pb_column][et_pb_column type=”2_3″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Tissue compartments<\/h3>\n

Haldane discovered that different parts of the body have different halftimes. They absorb and release dissolved nitrogen at different rates.
To account for these differences he constructed a mathematical model consisting of five theoretical tissues. These are called tissue compartments<\/strong><\/em>.<\/p>\n

These theoretical tissue compartments do not directly correspond to any particular body tissue. They are only used to simplify calculations.
Each compartment has a different halftime for the rate at which it absorbs and releases nitrogen (slow and fast compartments<\/strong><\/em>).<\/p>\n

Besides different halftimes, each compartment has a different M-value.
The slower<\/em> compartments have lower<\/em> M-values.
The faster<\/em> compartments\u00a0 have higher<\/em> M-values.
The M-values have been determined by performing Doppler tests on divers after actual test dives.<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n

Controlling compartment<\/h3>\n

If a diver becomes saturated on a shallow dive, the pressure gradient may still be lower than the M-value in the faster compartments. However, if the diver stays shallow for an extremely long time or if he makes several shallow dives in a short period, eventually the pressure gradient in the slower tissue compartments may become higher than the M-value.
The compartment that reaches its M-value first is called the controlling compartment<\/strong><\/em>.
On shallow dives, the controlling compartment is a slow compartment. On deep dives, the controlling compartment will be a fast compartment.<\/p>\n

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\ue007<\/span>
<\/strong><\/span><\/p>\n

Example<\/strong><\/span><\/p>\n

A diver makes a dive to 10 meters depth. The partial pressure of nitrogen in his breathing air is:
2 * 0.79 Bar = 1.58 Bar<\/p>\n

The fast tissue compartments in her body have a halftime of 5 minutes. After 6 * 5 minutes = 30 minutes, they will be saturated and reach a partial pressure of 1.58 bar. This is lower than the M-value of this compartment. Because the tissue compartment is saturated it’s partial pressure will never become higher than 1.58. Even if the diver stays at the same depth for a very long time.<\/p>\n

One of the slower tissue compartments has a halftime of 37 minutes. After 6 * 37 minutes = 222 minutes, this compartment will also be saturated and reach 1.58 Bar partial pressure. This may be higher than the M-value for this compartment, meaning the diver has an unacceptably high risk to develop DCS.<\/p>\n

This is why, on shallow dives, the controlling compartment will be a slow compartment.<\/em><\/p>\n

This is a very long dive (more than 3,5 hours) but you should remember that slow tissue compartments also release nitrogen slower during the surface interval. After a short surface interval, the slower compartments may not have released all nitrogen.<\/p>\n

When making several shallow dives in a short period, the controlling compartment will also be a slow compartment.<\/em><\/p>\n

<\/span><\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row make_equal=”on” _builder_version=”4.22.0″ _module_preset=”default” background_size=”initial” background_position=”top_left” background_repeat=”repeat” max_width=”100%” module_alignment=”center” custom_padding=”||||false|false” use_custom_width=”on” width_unit=”off” custom_width_percent=”100%” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” custom_padding=”||||false|false” global_colors_info=”{}” custom_padding__hover=”|||” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”40f87f69-68a0-4a74-8d3a-23f3acd6bdad” hover_enabled=”0″ global_colors_info=”{}” theme_builder_area=”post_content” sticky_enabled=”0″]<\/p>\n

When any compartment reaches its M-value the dive ends or it becomes a decompression dive. Remember that the M-values are calculated for surfacing at sea level which is why you need to apply special procedures when diving at altitudes above 300m.<\/p>\n

Remember: All decompression models are theoretical representations of dives. There is no direct relationship<\/strong><\/em> between the decompression model and the human body. Some divers are more susceptible to DCS than others. There is always some risk of DCS. This is why we teach divers to avoid diving close to the limits of their tables or dive computer.<\/p>\n

[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.22.0″ _module_preset=”default” locked=”off” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_column type=”4_4″ _builder_version=”4.22.0″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”][et_pb_text _builder_version=”4.22.0″ _module_preset=”default” global_colors_info=”{}” theme_builder_area=”post_content”]<\/p>\n