The VPM model

The VPM model is the result of many years of work by dedicated individuals, researchers, dive industry staff and technical divers. The various algorithms used in the model were developed over many years, initially in research work and later in a wider group in an open source environment. All work has been subject to peer review and the final work was completed in 2000. Erik Baker and Eric Maiken were central to bringing the model to completion. They added the final revision to VPM-B in 2002, which has become the standard in common use today.

The dive profile from a VPM-B profile is a one that includes both deep stops and modest amount of time in the shallow areas. The basic concept of a bubble model is to limit and control bubble growth and bubble sizes to smaller amounts through the ascent, thereby avoiding the damaging effects of any larger bubbles.

A significant amount of diver feedback and experience has demonstrated the VPM-B model is suitable for a wide range of dive profiles. The VPM-B model produces consistent decompression plans for the entire range of dives, and accurately intercepts the NDL limits as well.

The VPM-B/E model variation is for the extreme or extra long dives and exposures. It gives a more relaxed version of a profile for dives when extra safety is prudent. With bigger dives (typically more than 100 mins deco), the profile will diverge from the standard VPM-B, and produce a profile similar to a combined or overlapped VPM-B and Haldane plan. Divers who carry out the very long and deep dives, often prefer the additional margin of safety from this combination plan concept, and the VPM-B/E generates a plan to meet this requirement.

The VPM-B/FBO model variation (Fast Bail Out) is for the use with closed circuit diving and a bail out suituation. The purpose is to help reduce the required diluent gas volume during bailout (typically a 30 to 50% reduction). A Fast Bail Out ascent will reduce the time spent at the deeper stops, and cause the decompression to expand into the shallow stops. The changed ascent shape is still calculated within the context of the VPM-B model. These ascents are aggressive and have fewer deep stops than a regular plan, but VPM-B/FBO still has more deco time than a matching raw Bulhmann plan.

The VPM-B + GFS model combination (Gradient Factor Surfacing) produces another type of relaxed profile. The GFS takes a regular VPM-B profile and adds a second calculation from a ZHL-16 GF profile with the GF Hi value specified. From these two, the most restrictive ceiling / time is used. Like VPM-B/E, the GFS normally only takes effect on larger dives. The GFS will affect the last few stops by adding a few minutes to each.

Brief history of the VPM.

1974 - 1981 U of Hawaii

Series of research papers (15+) by Yount,D.E. Hoffman,D.C Kunkle,T.D. Strauss, R.H. D’Arrigo, J.S., Ingle, F.W., Yeung, C.M., and Beckman, E.L. Yeung, C.M. Paganelli, C.V., Gillary, E.W.,
Research paper titles include Bubble formation, Bubble nucleation in supersaturated fluids, Isobaric bubble growth, Skins of varying permeability, Determination of the radii of gas cavitation nuclei, Application of a bubble formation model to decompression sickness,
1982 - 1984
Research papers by Yount,D.E. Hoffman,D.C SGillary, E.W.
Titles: ...evolution, generation, and regeneration of gas cavitation nuclei, ...use of a cavitation model to calculate diving tables, ...microbubble fission in surfactant solutions, ...microscopic investigation of bubble formation nuclei
Varying Permeability Model (VPM) - Yount and Hoffman
VPM tables - Yount and Hoffman
Eric Maiken starts working the VPM code, and start formatting his own VPM program made with BASIC.
Eric Maiken starts diving the model in the 130-220ft depth range, with O2 decompression, and progressing to trimix to 250 ft.
Eric Maiken distributes his BASIC VPM program, to divers / researchers. Program is now multi-level and nitrox mix capable.
The Yount and Hoffman (1986) VPM algorithm was made freely available to programmers and researchers at the tek95 diving technology conference. Eric released his VPM program code at this time in the VBA format, with an Excel spreadsheet front end. Eric Maiken reported his experiences with non Buhlmann based deco.

The text from this conference "Bubble Decompression Strategies" later became an article in Deep Tech magazine by Win Remly and Curt Bowen.
Eric Maiken's program is now distributed in Mathematica and full trimix capable.
The VPM List (later named DecoList) is started by Rob Murray, to discuss and test progress in the work on the Eric Maiken's VPM model code. David Yount joins in discussions, pleased to see his research work in use.
Erik Baker (developer of the 1Gradient Factor model) joins the project.
Many well known researchers from other decompression models and projects, tech divers and industry leaders and others contribute to the progress of the VPM model. The VPM List grows to over 200 members.
VPM development progresses with David Yount, Eric Maiken, Erik Baker working on repetitive diving, and a paper for the Smithsonian conference on reverse dive profiles.
David Yount, UH physics and astronomy professor, dies in April at age 64.
The core VPM algorithm was finalized in June, 2000 when David Yount's preliminary algorithm for multiple VPM dives was presented as a poster
(.ppt format)
at the UHMS conference in Stockholm. At this time, the algorithm had advanced beyond Yount/Hoffman's 1986 paper to include multiple inert gases and switches, new dynamics in calculating the critical radius (for example, ascent and descent influence on critical radii), as well as tracking the effects of multi dives.
Erik Baker's Fortan VPM program codes finalized (public domain) with contributions from many involved in the past years. This becomes the standard implementation of VPM at the time.
Ross Hemingway (developer of the 2ZPlanner program) adapts the VPM Fortan codes by Erik Baker from its DOS console state, into a full Windows program. This is the first Windows program with VPM, and the general public has its first look and use of VPM profiles. The new program is named V-Planner and is released as a freeware in July.
VPM use in recreational tech diving grows. Model is adapted for use with CCR planning. Diver feedback and documented experiences grow. Initial feedback suggests the model is somewhat range bound in its profiles. Erik Baker starts work on a revision to the original model. This results in a change to the method of calculating ascent ceilings and how they are propagated through the ascent. The revision to the model is named VPM-B, and becomes the standard for VPM.
February: V-Planner with VPM-B released at the NAUI Deep Stop conference.
IANTD includes VPM-B tables into new CCR training courses.
VPM enters commercial work as an approved decompression program with the Danish Maritime Authorities.
V-Planner program further developed to include many of the current tech diving planning features and practices.
V-Planner and VPM/B is now widely used by tech divers in the USA & Canada, and continues to grow throughout the world.
Dave Shaw sets world record CCR depth of (270m at Boesmansgat cave) with VPM-B.
VPM-B/E model option introduced.
PDIC Brazil adds V-Planner and VPM-B model to its training.
GUE adds VPM-B model to its DecoPlanner program.
VR3 tech dive computer adds the VPM-B/E model name and emulates the VPM style output.
Cedric Verdier sets record 201m Meg rebreather dive in Sra Keow cave in Krabi Thailand using the VPM-B/E. Three months later Cedric Verdier dives to 176m on the Yamashiro, with VPM-B/E.
Cedric Verdier on a Meg and with VPM-B/E, along with Ben Reymenants
(unknown deco)
on OC, do a team dive to 226m and 239m in the Sra Keow cave in Krabi Thailand.

VPM-B and V-Planner added to the German TDI Trimix manual, and used in for all Decompression Procedures, Extended Range, Trimix and Advanced Trimix courses as official Decompression software.

V-Planner Live with realtime VPM-B and VPM-B/E calculations for a submersible dive computer, is added to the Liquivision X1 tech computer.
Matt Reed, Mike Taylor, Roger Ingebo, Paul Neilson dive to 110-120m on the Princess of Orient, outside Manila Bay, Philippines (7 dives total). All divers used VPM-B and Mike used a Liquivision X1 with V-Planner Live.

Pim van der Horst, Henrik Enckell, Per Bjorn Rakvag, Spyros Spyro and Cedric Verdier, using Meg's, DIRRebreather procedures and VPM-B deco profiles, carried out 10 dives total to the HMS Victoria located off Lebabon. Dive depths ranged from 100m with some team members reaching the bottom at 140m, and two members used X1's with V-Planner Live.
Created the V-Planner Live online data base. Divers can upload the actual dive profiles as recorded in the Liquivision X1, into the database. The database holds 11,000 dive profiles as of Aug 09, and continues to grows by 1,000 dives a month.

The VPM-B/FBO model variation added. The Fast Bail Out (FBO) is designed for CCR divers for use in bail out situations. It reduces the required diluent gas volume during bail out.
VPM-B and VPM-B/E added to the HeinrichsWeikamp DR5 dive computer as Multideco-DR5.
The V-Planner Live online data base now holds 50,000+ dives.
The Predator dive computer adds VPM-B model option.
Krzysztof Starnawski dives MultiDeco-X1 and VPM-B/E to 283m at Dahab Egypt, with a dual rebreather system.
The V-Planner amd MultiDeco online data base now holds 140,000+ dives.
MultiDeco-TDC added to the TDC-3 dive computer.

See also... VPM References, Eric Maiken's VPM decompression site (bubble model explanations). More Decompression topics.

1. Gradient Factors are in now use with many Bulhmann based algorithims, including DecoPlanner.
2. ZPlanner was a wrapper around the Zplan DOS program by the late Will Smithers.