Toxic Gases - H2S

Toxic Gases- H2S

Risk Management within PDCA cycle

Identify Hazards

Assess Risks

Control Risks

Recovery Measures

Focus: IDENTIFY and CONTROL

ContentsThe routes of entry of toxic gases into the body

Occupation exposure standards - definitions

The hazards of H2S, the harm it causes and where it is likely to be encountered on site

The hazards of other toxic / hazardous gases that may be encountered

Gas detection systems and their use

Other protective measures used to mitigate the effects of toxic gases

Contents

Routes of entry Occupational exposure standards - definitionsDetailed overview of H2SBrief overview of other toxic / hazardous gasesGas detection systemsOther protective measuresReview of ModuleEvaluation Test

Review Routes of Entry

Topic : Review Routes of Entry

Routes of Entry 1

Chemicals only harmful if on or in bodyRoutes of entry:

– Contact with bare skin or eyes – Breathing in chemicals– Swallowing chemicals

Skin

Breathing

Swallowing

Tissues

Skin

BloodstreamLungs

Target organsLiver

Kidneys

Heart

Brain

Routes of Entry-2

Toxic Gases

Inhalation is the main route for gas poisoning

Effects will vary depending on the gas involved

May cause irritation & injury to respiratory tract, lungs and skin or eyes

May cause systemic poisoning of specific organs

May cause both

Definition of DoseThe US Agency for Toxic Substances and Disease Registry (ATSDR) defines Dose as follows (for chemicals that are not radioactive):– Dose is the amount of a substance to which a person is

exposed over some time period.– Dose is a measurement of exposure.– Dose is often expressed as milligram (amount) per kilogram (a

measure of body weight) per day (a measure of time) when people eat or drink contaminated water, food, or soil.

– In general, the greater the dose, the greater the likelihood of an effect.

– An "exposure dose" is how much of a substance is encountered in the environment.

– An "absorbed dose" is the amount of a substance that actually got into the body through the eyes, skin, stomach, intestines, or lungs.

Occupational Exposure Standards - Definitions

Standards for Chemical Agents- Background

Few countries have the organisations and resources to develop maintain and review occupational exposure limitsMost countries base guidance on one of the following:– USA Occupational Health and Safety Administration (OSHA)

- Permissible Exposure Limits (PEL)– American Conferences of Government Industrial Hygienists

(ACGIH) – Threshold Limit Values (TLV) – UK Maximum Exposure Limits (MEL) and Occupational

Exposure Standards (OES) – French VLE/VME – German MAK/TRK

Standards are expressed either by volume – atmospheric concentration in parts per million (ppm) or by weight milligrams of substance per cubic metre of air (mg/m3)

What These Standards are

These standards are measures by which exposure to chemicals and physical agents are assessed

They are NOT an index of toxicity

What These Standards Mean

These standards are based on best information currently availableThey change as more information becomes available Not every substance has an established standard Good practice to keep exposure as low as practicable INSTEAD OF just below the standardConcentration based over reference period which according to current knowledge is unlikely to be injurious to health from continuous exposure

Limitations

OEL’s only based on inhalation No account of skin absorption or ingestion They apply to healthy adults NOT more sensitive individuals or groupsBased on data from North America & EuropeVariations in controlErrors in monitoring Synergistic effects – mixtures of various toxic gases

Time Weighted Average

Time Weighted Average (TWA)

Workplace exposure is rarely constantHarm related to dose – concentration and time Workplace exposure therefore “normalised” over a reference period to identify the average dose received over that periodThe reference periods are normally 8 hours and 15 minutes

Acute Exposure Guideline Levels -AEGLs

AEGLs are defined as the concentration of a substance in air that causes a specific level of biological effects in a defined population after a specified duration of exposure.AEGLs are intended to represent biological threshold exposure values for the general population. The availability of these levels provides guidance to those responsible for emergency planning and response to chemical accidents, as well as for prevention of accidents with possible adverse health effects.

Acute Exposure Guideline Levels - 1

AEGLs are established for single exposures during four different time periods, i.e., 30 minutes, and one, four, and eight hours. For each time period, three levels of effects are considered:

– AEGL – 1 is the level of a chemical in air at or above which the general population could experience notable discomfort;

– AEGL – 2 is the level of a chemical in air at or above which there may be irreversible or other serious long-lasting effects or impaired ability to escape; and

– AEGL – 3 is the level of a chemical in air at or above which the general population could experience life-threatening health effects or death.


Time scaling is used to help develop AEGL values for the four different time periods.A typical concentration-time-response curve (or dose-response curve) is shown below.



Concentration-time-response curves

1. Where data are available for the time periods of interest, then this data are used.

2. Since empirical data are rarely available for all AEGL-specified time points, the curves are extrapolated within and outside the time range of reported data.

A regression analysis is used to establish an “n” value, which determines the slope of the concentration-time-response curve, allowing for an estimate of the AEGL values for the time periods of interest.If supporting data are available, these numbers can be evaluated for reasonableness.Where empirical data are limited for deriving the “n” value, and there are limited supporting data, then a more conservative approach is used in developing the AEGL values for the different time periods.For example, n=1 is used for extrapolation from short to longer durations and n=3 is used for long to shorter durations.

Maximum Exposure Limits

Maximum exposure limits – MEL

The maximum concentration of an airborne substance averaged over a reference period, to which employees may be exposed under any circumstancesControl shall only be regarded as adequate if exposure is reduced so far as reasonably practicable and, in any case below the MELSTEL’s are assigned to substances which give rise to acute effects and should never be exceeded

Short Term Exposure Limits

UK Occupational Exposure Standards

Short Term Exposure Limit (STEL)

Dose averaged over 15 minutes

Concerned with reducing the risk of acute effects

Long Term Exposure Limits

UK Occupational Exposure Standards

Long-Term Exposure Limit (LTEL)

Total intake averaged over an 8 hour reference period

Protects against chronic effects

Threshold Limit Values - 1TLV’s are guidelines (NOT standards) prepared by the ACGIH to assist organisations in making decisions regarding safe levels of exposure to certain hazards in the workplaceTLV’s reflect the level of exposure that a typical worker can experience without an unreasonable risk of disease or injuryTLV’s are scientific opinion based solely on health factors with no consideration given to technical feasibility of economic factorsDetermined from a review of peer reviewed scientific literature

Threshold Limit Values - 2TLV -TWAThe TWA average concentration for an 8 hour day, 40 hour week which nearly all workers can be repeatedly exposed without adverse effectsTLV- STELThe 15 minute TWA that should not exceeded during any part of the working day even if the 8hr TWA is within the TLV . No more that 4 excursions a day are permitted and at least one hour should elapse between exposures TLV- CeilingThe concentration that should never be exceeded during any part of the working exposure

Permissible Exposure Limits

PEL’s are regulatory limits set to protect workers against the health effects of exposure to hazardous substances

PEL’s are enforceable by law in the USA

Based on TWA’s

H2S Overview

Hydrogen Sulphide Background

Very significant hazard for Agip KCO:

– North Caspian Oilfields generally have high H2S contents

– H2S will be present in many process areas

– Potential for exposure to H2S is high

– H2S potentially fatal

It can be found in natural environment from:

– decomposition of organic matter / wastes

– anaerobic processes

H2S solubility:

– It is soluble in oil and water

– Solubility changes with temperature

H2S toxicity:

– It affects a specific part of the brain stopping the drive to breath

Hydrogen Sulphide Properties

Typical Locations / Operations

Crude oil and gas wellsGas plantsTank vents and gauging pointsConfined spaces Anaerobic systems – waste water treatmentStagnant water Drilling & lifting operationsField maintenance of wellsWell injections

Typical Locations

H2S Characteristics - Toxicity

< 1 ppm - Detectable by smell

30 ppm - Eye and respiratory tract irritation

100 ppm - Loss of sense of smell

500 ppm- Within 15 minutes – dizzy, headache, nausea, pain; After 30 minutes loss of consciousness, death

>1,000 ppm Rapid loss of consciousness, death in minutes

Example of Concentration

One part per million (ppm) would beone teaspoonful in approximately 25 drums

H2S- Exposure Standards

LTEL 10 ppm (UK)

STEL 5 ppm (UK)

ACGIH TLV’s - LTEL 10ppm, STEL 15ppm (USA)

H2S Limits – WHO (1)World Health Organization Limits for H2S: established dose–

effect relationshipsmg/m3 ppm Effect 1400–2800 1000–2000 Immediate collapse with paralysis of respiration

750–1400 530–1000 Strong central nervous system stimulation, hyperpnoea followed by respiratory arrest

450–750 320–530 Pulmonary oedema with risk of death

210–350 150–250 Loss of olfactory sense

70–140 50–100 Serious eye damage

15–30 10–20 Threshold for eye irritation

Changes in haem synthesis have been reported at hydrogen sulfideconcentrations of less than 7.8 mg/m3 (1.5–3 mg/m3 average).It is not known whether the inhibition is caused by the low concentrations or by the cumulative effects of occasional peak concentrations.Most probably, at concentrations below 1.5 mg/m3 (1 ppm), even with exposure for longer periods, there are very few detectable health hazards in the toxicological sense.The malodorous property of hydrogen sulfide is a source of annoyance for a large proportion of the general population at concentrations below 1.5 mg/m3, but from the existing data it cannot be concluded whether any health effects result.

World Health Organization Limits for H2S

H2S Limits – WHO (2)

H2S Limits – EUBAlberta Energy and Utilities Board (EUB) Limits for H2S:

effects of H2S on people

Parts per million (approximate ranges)0.01-0.3 Odour is detectable

1-10 Moderate to strong odour. People may experience nausea, tearing of the eyes, headaches and loss of sleep following prolonged exposure. The effects appear to be reversible and not serious for the general population, although more susceptible individuals may respond more severely.

10-150 Increasing degree of irritation to eyes and lungs.

150-750 Severe health effects which may lead to death, become more likely as concentration and exposure time increase.

greater than750

Death may occur in minutes or less.

H2S in the Environment

High acute (short-term) toxicity to:– Aquatic life– Birds– Animals

H2S enters the environment from both natural and human processesIn air H2S reacts with other chemicals to be broken down. It takes about three days to happen.

H2S- Other Hazards

Pyrophoric scale:

• Reaction of H2S on steel in absence of air

• Spontaneously combusts in presence of air

• Source of ignition

• Gives off SO2

• Keep scale wet until disposed of to a safe place

Sulphide stress cracking:

• H2S and water exceeding a threshold partial pressure makes carbon steel susceptible to cracking

H2S First Aid

Flush Eyes With Water for 15 Minutes

Wash Skin With Soap and Water

Move Person to Fresh Air

Apply Artificial Respiration

ALWAYS SEEK MEDICAL ATTENTION

Other Toxic / Hazardous Gases

Other Toxic / Hazardous Gases - List

Sulphur Dioxide – SO2

Carbon Monoxide – CO

Methane – CH4

Carbon Dioxide – CO2

Colourless gasHeavier than air Irritating odourDissolves in water to form acid solution Produced in combustion of fossil fuels and some manufacturing processesHarms plants and treesCauses corrosion of metal and damages stone and masonry

SO2 properties

SO2 – Toxic effects

> 6ppm immediate respiratory tract and lung irritation High concentrations constrict bronchi and increase mucus flow affecting breathing Impair respiratory systems defenses against particles and bacteriaAsthmatics and people with bronchial problems may be affected at concentrations < 1ppm

In UK OES - 8hr TWA 2ppm, STEL 5ppm until 2003 Withdrawn as believed not to be adequate to protect occupational health Now need to reduce ALARP and if possible to below 1ppm (LTEL & STEL) OSHA PEL 2ppmACGIH TLV 2ppm

SO2 Exposure Standards

SO2 in the Environment

Low SO2 concentrations can:– harm plants and trees– reduce crop productivity Higher SO2 levels, and especially the acidic deposits from acid rain, can adversely affect both land and water ecosystems SO2 in the atmosphere is absorbed by soils and plants SO2 is captured within and below clouds. In certain circumstances it may raise the acidity of the resultant rain (acid rain)

CO properties

ColourlessOdourless Tasteless Only detectable by measuring instruments Chemical AsphyxiantHEADACHE SHOULD BE TAKEN AS WARNING SIGN THAT DANAGEROUS CONCENRATINS MAY BE PRESENT

Carbon Monoxide – CO

Product of incomplete combustion of fossil fuels Poor maintenance of equipment increases CO levels in exhausts Engines, heaters, compressors, burners common sources High risk in confined spaces

CO – Toxic Effects

Headaches, chest pains, muscular weakness, lethargySickness, diarrhoea, stomach painsSudden dizziness when standing upCan be fatal – and difficult to recognise due to lack of detectable physical propertiesLong term circulation effectsMay impair fertilityMay damage unborn foetusDelayed adverse effects possible

CO – Exposure Standards

OSHA PEL 50ppm

ACGIH TLV-TWA 25ppm

UK LTEL 30ppm

UK STEL 200ppm

CO in the EnvironmentCO is not considered a greenhouse gas, but it is a precursor to greenhouse gases. CO elevates the atmospheric concentrations of:– methane (a greenhouse gas)– ozone

At high levels, CO causes illness (fatigue, gastric upset) to animals. At very high levels, CO is life threatening. Long term (chronic) exposure to low levels of carbon monoxide may produce heart disease and damage to the nervous system.As in women, exposure of pregnant animals to CO may cause low birthrates and nervous system damage to the offspring.

Carbon Dioxide – CO2

Colourless OdourlessHeavier than air Present in atmosphere – 0.035% Represses respiratory system eventually causing death by asphyxiation At lower concentrations causes headaches and sweating followed by loss of consciousnessBy-product of respiration – excreted from the body in exhaled air Hazardous in confined spaces

CO2 Effects (1)Some people exhibit symptoms at 1.5% (15,000ppm)Short term exposure <2% not reported to be harmful 3-5% for 25 minutes increased breathing 7.5 % feeling of inability to breathe, increased pulse rate, headache, dizziness and disorientation10% for 1.5 minutes- eye flickering excitation, increased muscle activity and twitching>10% - breathing difficulty, I,paired hearing, nausea, vomiting strangling sensation loss of consciousness within 15 minutes

CO2 Effects (2)

Deaths reported after exposure to 20% Effects more pronounced upon physical exertionMay work synergistically with CO increasing the rate of binding with haemoglobinHigh concentration reported to cause stinging sensation in the eyes as well as visual distortion due to inhalation

CO2 in the Environment

CO2 is the most well known greenhouse gas.It is also the greenhouse gas man contributes to most, primarily through burning fossil fuels. The main CO2 sources are:– energy and industry sectors, transports, land-use change,

biomass respiration and biomass burningThe main CO2 sinks are:– plants, oceans, soils, sediments, rock and fossil fuel.

Methane – CH4

Natural Gas

Highly flammable

Flammable range LEL 5% UEL 15%

Simple asphyxiant by displacement of oxygen

No identified toxic effects

CH4 in the EnvironmentMethane is one of the well known greenhouse gases.The main CH4 sources are:– wetlands, termites, the oceans and decomposition of methane

hydrates present in marine sediments and polar regions, energy sector (methane releases during fossil fuel extraction and transportation), landfills/agricultural waste, ruminants, rice agriculture and biomass burning (burning is often carried out topromote regeneration of the vegetation).

The main sinks for CH4 are:– the atmosphere (methane in the troposphere reacts with

hydroxyl radicals, forming mainly water and carbon dioxide) and soils (where metanotroph bacteria use methane as a source of carbon).

Gas Detection Systems

Monitoring Devices

Fixed area gas detectors

Colorimetric tubes

Personal gas detectors

Hand held gas detectors

Area Detection Systems

Fixed detectors located in areas where toxic gas potentially present Signal to control room /satellite control rooms Alarm locally & control roomAudible and visual alarmsContinuous detection Can be vulnerable to process materials/steamMaintenance and testing Procedures for actions on activation

Air Intakes

Detectors in air intakes to control rooms and accommodation

Raises alarm and shutdown or switches air intake location

Maintains safe location for mitigation control actions

Some Examples of Detectors

Colorimetric Tubes - 1

The Classic The Classic ““Spot MeasurementSpot Measurement”” TechniqueTechniqueAir is sampled through a glass tube using a pumpAir is sampled through a glass tube using a pumpChemicals in the tube react with the gas to be Chemicals in the tube react with the gas to be measuredmeasuredColourColour change from reaction indicates change from reaction indicates concentration of gasconcentration of gasConcentration determined from a scale printed on Concentration determined from a scale printed on the tubethe tubeFilter Layers can either remove interfering gases or Filter Layers can either remove interfering gases or prepare the gas for measurementprepare the gas for measurementCan measure more than 500 gases & Can measure more than 500 gases & vapoursvapours

Colorimetric Tubes Colorimetric Tubes -- 2 2

Some cross sensitivities lead to ambiguous Some cross sensitivities lead to ambiguous resultsresultsNot an effective method for WARNINGNot an effective method for WARNINGCannot track changes in concentrationCannot track changes in concentration

Personal Gas Detectors

Portable gas detectors worn to protect individuals

Detect ONE specific toxic gas

Alarms both visual and audible

Robust units for routine use

Calibration and maintenance

Trained users

Hand Held Gas Monitors - 1

Portable monitors used for workplace detection

Confined spaces

Multigas detection

Oxygen , toxics, flammables

Trained users

Maintenance and calibration


Portable detectors used for monitoring workplaces

Confined spaces particularly important

Single/Multigas Capability

Suitable for OX / TOX / EX

Measures the CORRECT toxic gases

Clear warning signal

Simple to operate

Display clear with backlight


User Exchangeable Sensors for flexibility / maintenance

Electronic Pump (suitable for long distance sampling)

Different sampling options

Rechargeable Long Lasting Batteries

Rugged & Long Lasting Unit

Correct certifications

Protection Systems

Protection Systems

Proper engineering design

Management of Change

H2S sources identified

Reduce number of fittings to a minimum

Vents and drains to be routed to closed systems

Separate flare lines

Emergency Shut Down systems

Workplace controls and risk assessments

Individual Protection Systems

Know Escape RoutesTake heed of signs and warnings Use Positive Pressure Air-Supplied RespiratorsMonitor the area Have escape sets available Follow Work ProceduresUse the “Buddy” SystemVentilate if work is enclosed area Use Windsocks and be “Wind Conscious”

Types of Breathing Apparatus

BA for working

BA for rescue purposes

BA for escape purposes

Working SetsPositive pressure air-line BA the only option for maintenance in H2S areas or where other toxic gases expected Wearers to undergo a fit test and trainingFacial hair policyAir supply Air quality & testingCompressor maintenance Equipment maintenance and testing

Rescue Sets

Self Contained Breathing Apparatus – SCBA

Trained users

Proper fitting

Procedures

Cylinder Filling and Air supplies

Maintenance & testing

Escape Sets Mandatory requirement (with personal monitor)for working in H2S areas

Either carried by individuals or readily available

Full face mask preferred

Positive pressure sets available

Testing and maintenance

NEVER USE ESCAPE SETS FOR WORK OR RESCUE

Filter Respirators

Chemicals in cartridge filter or absorb dusts or toxic gasesCan become saturated and ineffectiveNeed to understand their usage and the protection they offerNeed to know the likely toxins to be protected againstNeed to know the concentrations that will be encounteredTraining, inspection and maintenance

Contingency Plans and Emergency Actions

Develop, implement and practice contingency plans Principles:• EVACUATE!• Safe refuge• Raise the alarm • Escape sets are for escape• Only Trained people equipped with Self Contained

Breathing Apparatus (SCBS) can remain in or Enter the Area

• Have a trained backup person equipped with SCBA• Mustering and personnel accounting

Toxic Gases - H2S

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