How to calculate confined space entry risk

Is the science and art of confined space entry gone, forgotten, or ignored? Here are some confined space risk assessment calculations.

When reading various procedures for confined space entry, the identification and the description is generally well done.

When one however gets to the:

  • clearing (gas/vapour/dust monitoring) of such spaces
  • frequency, type, and duration of monitoring of such spaces
  • entrants’ training, emergency procedures
  • self-rescue
  • equipment (including safety PPE) to be used
  • communication means,

I find the procedure is often very sparse, and sometimes downright hazardous.

Basics of confined space entry risk assessment

[This section is added to the post from comment by the author in response to a query, see below];
Lets start with basic mathematics; Volume of Confined space, square, round etc. Piping attached, blinded or blanked off included. If Inert, and has a bed of pyrophoric matter therein then amount of nitrogen therein to keep the nitrogen blanket, vs the amount of air and nitrogen constant flow out of tank, this would normally be down by a specialist contractor. If blanket broken, then high possibility of person and space bursting into flames.

O2 is self-evident. But for argument sake the vessel has benzene in it, the then because the OEL so low, the LEL would only serve its purpose well below the 10% of LEL, this would never achieve the OEL, so specialist PPE would be required, once again basic calculations, without adapting for atmospheric pressure e.g. from coast to JHB for example, or the difference in the calibration of the specific “explosion equipment calibration gas” etc, let us assume that in the space we have 10% of the LEL, assuming the LEL is 2%, then 10% of LEL is 0.2%, converted to ppm “all things being equal”, then 0.2% of a million is… way above the OEL.

Number of air changes, this is another calculation that is pretty easy, look on the fan drive for the relevant data, and can be verified from the exit of the confined space using a simple vane anemometer, and the shape and size of the exit.

Vapour Pressure, and paint specs are found in the technical specifications of the paint for instance, it will also include the carrier solvent properties that are the physical and not the chemical characteristic of the substance.

Spread rate, will give surface area, drying time, e.g. after 4 Hours X amount is flashed off, after 8 hours the next parameter may be given. Plug this into standard Industrial Hygiene calculations in Industrial Hygiene practice and calculate.

All Industrial Hygienists, and many CSP (America), CMIOSH (UK) study this in their degrees.

Some good books to refer to are:
The Industrial Environment: Its evaluation and Control
Industrial Ventilation – I think it is by ACGIH
Calculations for Industrial Hygienists
CSP Exam questions.
[end of additional text from the Comment column]

Confined Space Entry training

I went to find suitable training in this area after I went to an interesting talk on it last month. I found that there is very little in SAQA unit standards regarding this, two courses that I could find.

There are many other courses offered by various training institutions but none of them make a person competent.

This competency is an extremely wide term, and I found from experience it generally describes the following:

“a person who will take the blame, hopefully the lowest person in the organisation who will get off anyway”

If however I was to describe such a person as;

“a person who has a science related diploma/degree in health and safety, or a chemical engineer, or a degreed person who by the nature of his/her further training and found competent by an organisation (eg American Petroleum Institute – API) to do confined space chemical and hazard clearances both in chemical and non-chemical environments”,

would there be an uproar?

LoadConfined Space shedding

I have witnessed more so in South Africa that the levels of persons who do these tests look merely at the Lower Explosive Limit (LEL).

I often get told when I ask about this level and what it means, they say “it’s alright to go in”, (I am happy I am not going in), followed by “I have been doing confined space entry for years” – (yes, but incorrectly and at high risk).

Asking which parameter should be checked first, I often get “Lower Exposure Limit (LEL)”, (about 50% of the time) followed by “oxygen”.

confined space entry
Have all the confined space entry skills gone down a hole?

When asking about specifics such as those items that can be measured by the reading instrument, very little or insufficient knowledge is predominant.

Not all parameters can be checked using a direct reading instrument, especially explosive dust particles, and many other chemicals.

Wetting down seems always to be the answer, or, we “have never had a problem before”! Neither have many other companies who have then had fatalities, including secondary fatalities of persons TRYING to perform a rescue.

Game of Thrones Confined Space Entry

Just to let you know that after the Hazard Identification / Risk Assessment order should be:

  1. Oxygen Level
  2. LEL
  3. Toxic components.

And before this hierarchy, various inspections and documentation are required, especially if on a chemical plant. In construction, many confined spaces exist, and extend beyond the boundaries of the physical space.

On a chemical or petro-chemical plant, there are;

  • P&ID’s,
  • internal configuration drawing of the space to be entered,
  • sampling points in relation to the hazard,
  • sampling methodology,
  • possibility of internal release of hazardous materials,
  • wearing of personal protective equipment,
  • a trained stand-by that will NEVER enter the confined space (standby’s job is to raise the alarm),
  • rescue team on standby and in communication directly.

Not with a Shout and a Prayer

These are some basics, (not mentioned in the regulations), and then there are specific space entries, such as “inert entries”, “water entries” and the like.

Our confined space entrants are usually happy to acknowledge that there is a permit, and off they go, (obviously a non-specific medical has been done), the chaps can enter, and they do.

Hey, we forgot mechanical ventilation, the number of air-changes required per hour, and the need for portable local exhaust if necessary. Leave that, we will do it next time?

Ignorance is bliss

In one country I was misled to by a South African Safety Manager who stated that the air change calculations had been done, and that the concentrations inside the vessel were acceptable as they were monitored.

This was on day one of my engagement. After 3 days, and a near miss incident, I re-calculated the ventilation, reviewed the process, and discovered that none of the persons knew how to do the calculations, nor read the monitoring equipment correctly.

They did not calculate the vapour hazard ratio, or even knew how much paint was used, the composition thereof, or the amount that was flashing off each hour.

They certainly did not know the chemical and physical properties of the chemical used. I decreed that only I could sign off a permit to work (PTW) for a confined space, whic is not the ideal situation.

Who clears these spaces and what knowledge and skills does one need to have to be deemed competent?

Perhaps answers other than Occupational Hygienists may surface in the replies? Perhaps I have misread the definition of competence?

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Shane Lishman

Occupational Health & Safety Specialist
Shane Lishman CMIOSH OSHCR SIIRSM EHRB IoD(UK) Saiosh COSHPROF has over 30 years experience in HSE system development, implementation and HSE project management.

4 thoughts on “How to calculate confined space entry risk

  1. So a nightingale and a dust mask won’t cut it? ; )

    —- Editor notes; The job spec may require a canary and a flame-proof torch.

    1. Afraid not. I have seen in my career many confined space deaths. One was a triple fatality, that I investigated, mentioned before on this site somewhere.

  2. A beneficial writeup sir. Can you outline the methods to calculate all the relveant parameters regarding work in confined space?

    1. Hi, this sounds like a challenge to me, but yes I can.

      Lets start with basic mathematics; Volume of Confined space, square, round etc. Piping attached, blinded or blanked off included. If Inert, and has a bed of pyrophoric matter therein then amount of nitrogen therein to keep the nitrogen blanket, vs the amount of air and nitrogen constant flow out of tank, this would normally be down by a specialist contractor. If blanket broken, then high possibility of person and space bursting into flames.

      O2 is self-evident. But for argument sake the vessel has benzene in it, the then because the OEL so low, the LEL would only serve its purpose well below the 10% of LEL, this would never achieve the OEL, so specialist PPE would be required, once again basic calculations, without adapting for atmospheric pressure e.g. from coast to JHB for example, or the difference in the calibration of the specific “explosion equipment calibration gas” etc, let us assume that in the space we have 10% of the LEL, assuming the LEL is 2%, then 10% of LEL is 0.2%, converted to ppm “all things being equal”, then 0.2% of a million is… way above the OEL.

      Number of air changes, this is another calculation that is pretty easy, look on the fan drive for the relevant data, and can be verified from the exit of the confined space using a simple vane anemometer, and the shape and size of the exit.

      Vapour Pressure, and paint specs are found in the technical specifications of the paint for instance, it will also include the carrier solvent properties that are the physical and not the chemical characteristic of the substance. Spread rate, will give surface area, drying time, e.g. after 4 Hours X amount is flashed off, after 8 hours the next parameter may be given. Plug this into standard Industrial Hygiene calculations in Industrial Hygiene practice and calculate.

      All Industrial Hygienists, and many CSP (America), CMIOSH (UK) study this in their degrees.

      Some good books to refer to are:
      The Industrial Environment: Its evaluation and Control
      Industrial Ventilation – I think it is by ACGIH
      Calculations for Industrial Hygienists
      CSP Exam questions.

      If you would like me to further elaborate I will, but one first needs to know the basics.
      Regards
      Shane

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