It is extremely important that the Quality Cabin Environmental Air System provides the correct Positive Pressurisation of the Cabin. It is the External Air Supply Unit of the Quality Cabin Environmental Air System (not the Recirculation Unit), that is responsible for ensuring adequate / optimum Positive Pressurisation of the Cabin.
- There is no Australian Standard for minimum / maximum Cabin Pressurisation.
- EN474-1:2014-03- Earthmoving Machinery Safety- Part 1 states 50 pascal.
NIOSH (National Institute of Occupational Safety and Health) state “reasonable range” of 20-60 pascal".
- NIOSH have also complete tests that depict that a machine / vehicle travelling at 60 kph will equal an external Wind pressure of 100 pascal on the Cabin.
To meet todays and ever- evolving OH&S Standards we suggest that Cabin Pressure should exceed >80 pascal, with an optimum of 120-150 pascal. Also to avoid Over- Pressurisation of the Cabin then we also design our Q-CABAIR™ Quality Cabin Environmental Air Systems for a maximum Cabin Pressure of 200 pascal
Important note: Also just as essential is to Monitor the Pressure inside the Cabin using a In- Cabin Pressure Monitor Sensor / Alarm Unit (ICPS).
These aspects are discussed in further detail below.
Positive Cabin Pressurisation
- Positive Cabin Pressure avoids the risk of Contamination entering the Cabin- especially during operation of Mobile Plant (eg Door seals will open / close during movement).
- Excessive Cabin pressure can cause Operator headaches, damage eardrums and will damage / deform Cabin Seals.
- Excessive Cabin Pressure can also indicate that the Cabin is too well sealed and so Co2 Concentration can occur.
- Care should be taken to ensure that the design of the Recirculation Air Unit does not reduce Cabin Pressure (eg leakage in inflow / outflow of the Air Flow circuit), which will in turn cause a negative pressure in the Cabin and ingress of Contamination.
- Cabin Pressure should be set 30-50 pascal over the minimum required set- point Cabin Pressure. This is to allow the In- Cabin Pressure Monitor Sensor / Alarm Unit (ICPS) to activate and alert at a reasonable Filter Element loading to signify its replacement.
For example, if we required a minimum Cabin Pressure of 100 pascal then:
- The Quality Cabin Environmental Air System should be configured to achieve a Cabin Pressure of 130- 150 pascal.
- The ICPSensor is set to Alert the Operator when the set- point alarm is set at the minimum Cabin Pressure- in this case 100 pascal.
- If the Cabin Pressure is not set to 30-50 pascals above the minimum to allow for Filter Element loading, then this will cause premature / expensive Filter Element replacement and or Cabin under- pressurisation.
Cabin Pressure Monitoring.
A qualified In- Cabin Pressure Monitor Sensor / Alarm Unit should be installed as part of Quality Cabin Environmental Air Systems so as to ensure that pressure in the Cabin is maintained at the optimum level.
The Quality Cabin Environmental Air System's ICPSensor should:
- Monitor and warn the Operator if Cabin Pressure falls (or increases) below the safe set- point.
- The External Air Supply Unit provides the Fresh Air as well as the Positive Pressure inside the Cabin. As the Filter Media / Element becomes loaded with contamination then Air flow / Pressure will begin to diminish inside the Cabin. Should the set- point Cabin Pressure diminish to unsafe levels then ingress of particulate can occur.
- In addition, as Cabin Pressure diminishes, so does the Fresh Air Flow and so harmful Co2 Concentration can rapidly occur inside the Cabin .
- The In- Cabin Pressure Monitor Sensor / Alarm Unit is to provide the Operator with an indication that Cabin Pressure has diminished to a unsafe level that could be a result of Seals needing maintenance- but in most cases it signifies that the External Air Filter Element is loaded (restrictive airflow) and so needs replacement.