Types of gases
Hydrogen sulphide
Carbon monoxide
Oxygen
Flammable gases
Which is each gas measured in
Hs- Stel and TWAPpm and LEL%
Co - Stel and TWA ppm and LEL %
Oxygen - %
LEL - %
Hydrogen sulphide levels
STEL - 10pm
The weighted average - 5ppm
Lower explosive limit - 4.3%
Carbon monoxide levels
STEL - 100ppm
The weighted average - 20ppm
Lower explosive limit - 12.5%
Oxygen
19.5 low alarm level
23% high alarm level ( oxygen rich )
Low alarm means other gases in the area
High alarm means materiel that might not flammable now can be , an normal materials burn vigorously
Lower explosive limit
This detects flammable gases
10% LEL
20% UEL ( deflagration )
Calibrated with methane at 5%-15% , set higher than methene and will detect other gases that’s why set higher
Incidents we use the gdm for
Hazmat incidents
Dampening and cutting away
Working at head of aerial
Grass fires
Eco
Explosive risks ( flammable gases(
What is
Stel
Twa
Lel
Stel - measures toxicity over 15 minute peroid
Twa- Measures toxicity over 8 hours
Lel - measures flammability and its lowest concentration of gas and vapour that will cause deflagration in the air
How it’s measures?
There are 4 gases it detects
And it uses each one of the measurements to detect it in a different way
twa and stel - measure the toxic of hydrogen sulphide and carbon monoxide
Lel - measure the flammable gases and at what point they can cause deflagration
Oxygen - detect when there is another gas in the air, also when it is too oxygen rich which can cause other materials to ignite more easily
Also produced a high or low reading when a gas is really high or lower
What is hydrogen sulphide ?
Colourlos toxic and flammable gas
Smells of rotten eggs
Toxic and corrosive, can cause explosive mixture in air
Slightly heavier than air
What’s is carbon monoxide?
Colourslouss and odourless toxic gas ( flammable when in high concentrations of air )
Oxygen levels
21% air normally is
At 19.5% ba is required
23% OL / upper limit
What is hydrogen sulphide measured in?
Measured in ppm and lel
Where can you find hydrogen sulphide? And how is it formed?
Occurs naturally along side petroleum and a natural gas caused by rotting biological materials
Found in sewers and drains
What happens when you breathe in carbon dioxide?
Breathing it can make you unwell, dizzy, lightheaded, red flush
Can be fatal if reached high levels in blood
How is carbon monoxide formed? And Where can you find it
produced by incomplete combustion
From a faulty boiler , near fireplaces, at fires
What is carbon monoxide measured in
Measured in ppm, and LEL
Who and Where do you where the gdm?
Officer
Right hand side of tunic
Can be given to firefighters when necessary
What happens when oxygen reaches 23%
Oxygen OL is shown , and high
What happens when oxygen reaches 19.5%
Low alarm shows
And 19.5%
Flashes and beeps and vibrates
What does it mean when high shows
Low or high will show and then and measurement will show
Oxygen 23% is reached OL
Hs and co high indicates immediate danger to life
Flammable gases / uel is reached
What does it mean when low shows
Low or high will show then a measurement will show
Low means
Oxygen 19.5% and another gas is in air
Hs and co , initial exposure danger
Flammable gases is lel
Overall indicators
A low or high will show
A stel or twa will show
And then the measurement of the specific gas will show .
So you match up the gas with what it’s monitoring
Zero gdm
Needs to be zero’s at the start of day shift
In clean air
Won’t work Probally if air is not clean
Double click middle
