ndl {scuba}

No-Decompression Limit

Description

Compute the No-Decompression Limit (NDL) for a dive to a specified depth, under a Haldane-type decompression model.

Usage

ndl(depth, g=air, prevstate=NULL, model = "DSAT")

Arguments

depth

Depth (in metres) for which the NDL should be computed. A single number or a numeric vector.

g

Breathing gas for the dive. An object of class "gas".

prevstate

Optional. Initial state of the diver. A data frame containing the tissue saturations for each tissue compartment in the model, at the start of the dive. Defaults to the state of a diver with no previous dive history.

model

The decompression model. Either an object of class "hm", or a character string giving the name of one of the standard Haldane-type models. Options are "DSAT", "USN", "Workman" and "ZH-L16A".

Details

The No-Decompression Limit (NDL) for a given depth d is the maximum duration of a No-Decompression dive to depth d.

A No-Decompression dive is one which can (theoretically) be aborted at any time without requiring staged decompression. Equivalently, in a No-Decompression Dive, the Nitrogen saturation in each of the diver's tissue compartments never exceeds the maximum Nitrogen saturation tolerated at sea level (known as the surfacing M-value for that compartment).

This algorithm computes the NDL for a dive to the given depth, or for several possible alternative dives to the given depths, based on the specified decompression model. The NDL is determined by the halftimes and the surfacing M-values for all the compartments in the model.

If the breathing gas g contains Helium, then model must include compartments for Helium. Similar calculations apply in this case.

The argument prevstate represents the tissue saturation of the diver at the start of the dive. It should be a data frame, with one row for each compartment of the decompression model, and one column for each inert gas (N2 and/or He). Such data frames are usually generated by saturated.state or haldane.

Value

Numeric vector, of the same length as depth, giving the No-Decompression Limit in minutes for each depth. Infinite values are possible.

The value also has an attribute called "controlling" which identifies the controlling tissue (the tissue for which the M-value is reached).

Warning

This is not intended for use as a scuba diving table! The NDL calculated here is not the same as the NDL indicated in any published scuba diving table. For example, the NDL calculated by this algorithm using the halftimes and M-values of the DSAT model, may be longer than the NDL published in the DSAT Recreational Dive Planner. Infinite values of NDL may be returned in some cases.

Author(s)

Adrian Baddeley [e-mail].

See Also

scuba.disclaimer, haldane, showstates, saturated.state

Examples

  # NDL for a dive to 15 metres
  ndl(15)

  # NDL for a dive to 24 metres on EANx 32
  ndl(15, g=nitrox(0.32))

  # NDL for a dive to 60 metres on Trimix 15/50 under ZH-L16A model
  ndl(70, g=trimix(0.15, 0.5), model="Z")

  # NDL for a repetitive dive on air to 15 metres, following an 
  # 18-minute air dive to 30 metres and half-hour surface interval
  firstdive <- dive(c(30,18), c(5,3), c(0,30))
  ndl(15, prevstate=haldane(firstdive))