Although the standards state that anyone of any age, with an interest, may join the Primary and Secondary Care, CRP and AED or Care for Children programs you must be careful about accepting children.
The key phrase for me is 'with an interest'. If a child isn't showing an interest in the skills required in the programs and has an understanding of the key concepts, they may not be suitable for inclusion in the training just yet. This is naturally not linked to specific age as children develop both physically, mentally and more importantly, emotionally at very different rates.
One of the most famous invasive species brought by humans into a new ecosystem is the Cain Toad in Australia, which continues to be highly destructive to this day.
The Asian Carp and Zebra Mussel are invasive species currently causing damage to local ecosystems where they have introduced and most infamous to the diving community are the Lion Fish with no natural predators in The Carribean Sea, depleting local fish species and causing harm to that ecosystem.
There are six halftimes to every tissue compartment - if the halftime for the specific compartment is 30 minutes it will take 30 minutes for it to become 50% saturated, another 30 minutes for the compartment to become 75% saturated and so on for another 4 halftimes until reaching saturation.
So six 30 minute halftimes will take 180 minutes to reach saturation which is 3 hours.
Exposure protection is always a very personal choice; some people feel that wearing a wetsuit in tropical waters in temperatures above 25 degrees Celcius feels restricting and unnecessary while others insist on long wetsuits in the same waters.
PADI's Encyclopedia of Recreational Diving along with other student materials have a guide for which exposure protection is recommended based off water temperatures which can be very helpful if you're diving in new environments or have students partaking on a program in a new diving location.
It's important to understand the concept of dead air in the world of diving. We effectively extend the dead air space with the addition of a snorkel or regulator and breathing deeply and slowly helps us to clear the space so we may breathe a fresh breath every time to inhale.
Having a poorly maintained regulator can make it difficult to clear the extended dead air space in the second stage. This can result in hypercapnia; an excess of carbon dioxide in the blood which should be avoided whilst diving.